Drilled Shaft Tutorial

Drilled Shaft Tutorial Welcome

U.S. Department of Transportation, Federal Highway Administration

Transportation Curriculum Coordination Council

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�❍ Welcome ● Contents ● Chapter 1 ● Chapter 2 ● Chapter 3 ● Chapter 4 ● Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Welcome to the Drilled Shaft

Inspector Tutorial

To start the course, you can click on the Contents heading to the left or you can click on the Chapter 1 heading to the left.

Read each chapter carefully so you are prepared for the quiz at the end of the chapter.

This tutorial was co-funded by the FHWA and Florida Department of Transporation.

This tutorial has been developed as a companion training aid for NHI Course #132070A, Inspection of Drilled Shaft Foundations. It is recommended that this tutorial be completed prior to attendance at the NHI Inspector Qualification Course. Difficulties encountered during the completion of the tutorial and associated quizzes should be discussed and resolved with the participant's supervisor prior to attending the course to ensure successful completion of the Qualification course and associated examination.

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Drilled Shaft Tutorial Welcome

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Drilled Shaft Tutorial Table of Contents


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● Welcome �❍ Contents ● Chapter 1 ● Chapter 2 ● Chapter 3 ● Chapter 4 ● Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Table of Contents

● Welcome ● Table of Contents ● Chapter 1. Why a Tutorial ● Chapter 2. What is a Drilled Shaft ● Chapter 3. Drilled Shaft Construction Methods ● Chapter 4. Drilled Shaft Equipment and Tools ● Chapter 5. The Inspector's Role ● Chapter 6. Contractor and Equipment Arrive on Site ● Chapter 7. Shaft Excavation and Cleaning ● Chapter 8. Rebar Cage Fabrication and Positioning ● Chapter 9. Concrete Operations ● Chapter 10. Post Installation Testing ● Appendix A. Glossary ● Appendix B. Inspector Math Tips Sheet

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Drilled Shaft Tutorial Chapter 1


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● Welcome ● Contents �❍ Chapter 1 ● Chapter 2 ● Chapter 3 ● Chapter 4 ● Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Chapter 1

Why a Tutorial?

Contents

● Why a tutorial was developed. ● the Inspector means to the process.

The tutorial is based upon the FHWA Publication IF-99-025, Drilled Shaft Construction Procedures and Design Methods, including Chapter 15, Guide Specifications

DRILLED SHAFT FOUNDATION INSPECTOR'S QUALIFICATION COURSE

Federal Highway Administration

NHI Course 132070

Over the past decade, the Federal Highway Administration (FHWA), in

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association with State Transportation Departments (DOTs), has increased the focus on "Quality" in construction and design of transportation related projects.

As part of this program, they have developed and instruct more than 100 courses dealing with the full range of transportation issues, from planning to construction.

Recently enacted Federal regulations (23CFR 637B) requires that all testing and inspection during construction be performed by qualified personnel. In response to this legislation, the FHWA and DOTs established training programs, with courses specifically designed and focused to the Inspector's needs.

One of the qualification courses developed is the FHWA/NHI Course No. 132070, Drilled Shaft Inspector's Qualification Course. This three-day course focuses on the Inspector's duties and responsibilities during the drilled shaft construction process. Beginning with background information related to construction methods, equipment and tools, the course then takes the Inspector through each step of the process, pointing out specific related responsibilities and methods to assist the Inspector in achieving their goal- a quality constructed drilled shaft foundation in accordance with the Plans and Specifications. The course concludes with a written examination on the material covered.

This tutorial was developed to prepare potential and experienced inspectors for attendance at the course. The goal being to provide basic drilled shaft construction and inspection information of such value that course attendees have an increased potential for successfully completing and passing the course.

The Inspector serves as the link between the Engineer and Contractor. The Engineer desires that the Contractor construct the project in accordance with the Plans and Specifications and the Contractor desires to build the the project in accordance with the plans and specifications. So both the Engineer and Contractor have the same goal, getting a quality project constructed, and someone needs to be the link that ensures this is accomplished.



Engineer

Inspector

Contractor

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● Welcome ● Contents ● Chapter 1 �❍ Chapter 2 ● Chapter 3 ● Chapter 4 ● Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Chapter 2

What is a Drilled Shaft? Contents:

● What is a drilled shaft. ● Drilled shaft uses. ● Advantages & Disadvantages of Drilled Shafts.

A Drilled Shaft is a deep foundation that is constructed by placing fluid concrete in a drilled hole.

Structures can be supported by a variety of foundations. The selection of the foundation system is generally based upon several factors, such as:

● Loads to be imposed ● Site subsurface materials ● Special needs (high lateral capacity, etc. ● Cost

Drilled shafts (also called caissons, drilled piers or bored piles) have proven to be a cost effective, excellent performing, deep foundation system, that is utilized world-wide. Typically they are used for bridges and large structures, where large loads and lateral resistance are major factors.

Advantages

● Economics ● Minimizes pile cap needs ● Slightly less noise and reduced vibrations ● Easily adaptable to varying site conditions










● High axial and lateral loading capacity

Disadvantages

● Extremely sensitive to construction procedures ● Not good for contaminated sites ● Lack of construction expertise ● Lack of Qualified Inspectors

End Bearing

Drilled shafts can be designed as "End Bearing" meaning the load is carried by the base or "end" of the shaft.

Friction

Shafts design for having their load dissipated throughout the materials they are formed into are called "Friction" shafts. The site subsurface soils the shaft are installed into "grab" the sides of the shaft, much like when you step in mud and try to pull your foot out.




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● Welcome ● Contents ● Chapter 1 ● Chapter 2 �❍ Chapter 3 ● Chapter 4 ● Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Chapter 3

Drilled Shaft Construction Methods Contents

This Chapter contains information on the three methods of drilled shaft construction.

● Dry Shaft ● Wet Shaft Construction ● Cased Shaft Construction ● A short quiz is provided at the end of the Chapter.

Each of these methods is different and has their own potential problem areas and applicability. It is important for the Inspector to have an understanding of each of these processes to facilitate inspection of the shafts during construction.

What is a Dry Shaft

A shaft excavation that can be excavated to its designed depth without the need for slurry or casing.

he dry construction method is used at sites where the ground water level and soil and rock conditions are suitable to permit construction of the shaft in a relatively dry excavation. and where the sides and bottom of the shaft may be visually inspected by the Engineer prior to placing the concrete.

The dry method is by far the least expensive method for drilled shaft construction. Given the choice of drilling methods, Contractors will try the dry method even in soil or rock of dubious quality.

Dry construction is generally defined by an amount of water accumulation permitted over a specified time period.










Photograph of a dry shaft.

Note that the Inspector can visually inspect the bottom of the shaft.

● In place Soil/rock will keep the hole walls from collapsing. ● Construction of the shaft can be in relatively dry conditions.

Dry Shaft Construction Process

The dry method consists of drilling the shaft excavation, removing accumulated water and loose material from the excavation, placing the reinforcement cage, and concreting the shaft in a relatively dry excavation.

What is a Wet Shaft

Often called the "slurry-method", wet shaft construction is when a slurry or water is used to keep the hole stable for the entire depth of the shaft.



Photograph of an Inspector sounding a wet shaft with a weighted tape.

Note the slurry in the hole. The Inspector's unable to visually inspect the bottom of the shaft, as with the dry shaft seen earlier

When Used

● When a "dry" excavation cannot be maintained ● When In-place soil/rock is unstable and deforms or collapses ● When loose material and accumulated water cannot be removed

Wet -vs- Dry

● Wet is more expensive ● Wet requires more Contractor expertise ● Wet requires more equipment Wet is when there is more than 12" of accumulated water in the bottom of the shaft (typically) ● Wet precludes visual inspection of the bottom of the shaft by the Inspector

Wet Shaft Construction Process

Unlike the dry construction method, in this situation the water table may be above the shaft tip elevation or the geology consists of unstable or "caving" soils. Think of trying to dig a hole at the beach or lake near the water's edge. The hole stays open until you reach or get just below the water table or waterline. Then what happens? It collapses.

Well the same goes for drilled shafts excavated below the water table or in unstable soils. During the drilling of the hole, a slurry is introduced that "stabilizes" the sides of the hole or casing is installed and prevents the soils from collapsing into the hole.

Upon reaching the designed shaft tip elevation, the hole is cleaned, then the rebar cage placed.

Unlike the dry shaft method, the concrete is being placed "under the water" and therefore a tremie is lowered into the hole and the concrete placed through the tremie, which is carefully removed a little at a time to avoid "breaching" the concrete.



Types of Wet Shaft construction

There are two types of "wet" shaft construction:

The Static Process The Circulation Process

● Drilled down to the piezometric level ● Slurry introduced ● Cuttings are lifted from the hole

● Hole is drilled ● Slurry level maintained at the ground surface ● Cuttings and sand, is circulated to the surface, where it is cleaned and

reintroduced down the hole.

What is Slurry What Does the Slurry Do?

● Maintains a Stable Borehole Prior to Concreting ● Maintains High Effective Stresses in the Soil while the Hole is Open (Retard Softening or Loosening) ● Facilitates Removal of Cuttings in "Circulation Drilling"

Slurry is the fluid introduced into the excavation to assist in maintaining hole stability. Generally, three basic types of "slurries", Mineral, Polymer and Water, are employed in drilled shaft construction.

In some instances, though not recommended, a blended slurry, consisting of mineral and polymer slurries is employed.

● Mineral Slurry

Mineral Slurry is made from naturally occurring clay minerals.

Natural mineral clays: Bentonite, attapulgite and sepiolite

Bentonite slurries have been used commonly in drilled shaft construction in the United States since the 1960's. Other processed, powdered clay minerals, notably attapulgite and sepiolite, have been used on occasion in place of bentonite, usually in saline ground water conditions. However, Bentonite is the most common Bentonite and other clay minerals, when mixed with water in a



proper manner, form suspensions of microscopic, plate-like solids within the water. This suspension, in essence, is the drilling slurry. If the fluid pressures within the slurry column in the borehole exceed the fluid ground water pressures in a permeable formation (e.g., a sand stratum), the slurry penetrates the formation and deposits the suspended clay plates on the surface of the borehole, in effect forming a membrane, or "mudcake" that assists in keeping the borehole stable.

This photograph shows bentonite slurry (in the bags) being added to the mixing tub on a small project

● Polymer Slurry

Polymers are semi-synthetic or totally synthetic chemical slurries.

Drilling slurries can also be made of mixtures of chemicals called polymers and potable water. Polymers have been used in preference to bentonite in well drilling for some time in soil profiles that contain considerable clay or argillaceous (clay-based) rock, because bentonite slurries have a tendency to erode clayey rocks and to produce enlargements and subsequent instabilities in the boreholes. Polymer slurries require less conditioning before reuse than bentonite slurries and can be disposed of more inexpensively than bentonite slurries.

It is also important that polymers be kept out of contact with cement as much as possible during the construction process, since cement will cause the polymer to agglomerate.

Pictured here is one of the popular brands of Polymer slurry.



● Water

Water is used in some areas as the drilling fluid, in lieu of mineral or polymer slurry.

In certain geologic conditions, water when combined with the naturally occurring subsurface materials creates it own "slurry".

Generally, the use of water must be approved by the Engineer.

A misconception by many is that because water is being used, slurry testing is not necessary. However, many local specifications mandate that if water is used, it must still meet certain slurry properties and the only way to determine the specific properties values is to test.

In some instances, though not recommended, a blended slurry, consisting of mineral and polymer slurries is employed.

What is a Cased Shaft

The casing method is often used either when shown on the plans or at sites when construction methods are inadequate to prevent hole caving or excessive deformation. In this method the casing may be either placed in a predrilled hole or advanced through the ground by twisting, driving or vibration before being cleaned out. Casings and liners play an important role in the construction of drilled shafts, and special attention must be given to their selection and use.

Casings are tubes that are relatively strong, usually made of steel, and joined, if necessary, by welding. Liners, on the other hand, are light in weight and become a permanent part of the foundation. Liners may be made of sheet metal, plastic, or pressed fibers. While their use is much less frequent than that of casings, liners can become important in some situations.

Common situations where casing is used are:

● In generally dry soils or rocks that are stable when they are cut but which will slough soon afterwards. In such a case the borehole



is drilled, and casing (a simple steel pipe) is quickly set to prevent sloughing. ● When there is a clean sand below the water table underlain by a layer of impermeable limestone or low permeability clay into

which the drilled shaft will penetrate. In this case, since the overlying sand is water bearing, it is necessary to seal the bottom of the casing into the underlying rock/soil to prevent flow of water and caving of soils into the borehole.

This picture shows temporary casing being inserted in a pre-drilled hole.

Types of Casing

Temporary Casing

Temporary casing is used to retain the sides of the borehole only long enough for the fluid concrete to be placed. The temporary casing remains in place until the concrete has been poured to a level sufficient to withstand ground and groundwater pressures. The casing is removed after the concrete is placed. Additional concrete is placed as the casing is being pulled to maintain the pressure balance. Thereafter, the fluid pressure of the concrete is assumed to provide borehole stability.

Permanent Casing

The use of permanent casing is implied by its name; the casing remains and becomes a permanent part of the foundation. An example of the use of permanent casing is when a drilled shaft is to be installed through water and the protruding portion of the casing is used as a form. A possible technique that has been used successfully is to set a template for positioning the drilled shaft, to set a permanent casing through the template with its top above the water and with its base set an appropriate distance below the mudline, to make the excavation with the use of drilling slurry, and to place the concrete through a tremie to the top of the casing.

This photograph shows a vibratory hammer being lowered to attached to a piece of casing for installation in the hole.

Note the casing is marked in 5 foot intervals. At the top, 1foot increments are marked to facilitate more accurate measurement as the casing nears the bottom.



Cased Shaft Construction Process

Drill- hole is advanced using slurry through the caving soils

Case- casing is then installed through the caving soils and drilling continues to desired depth

Clean- slurry and cuttings removed from the hole

Position- rebar cage is positioned in the hole

Place- concrete is placed. If temporary casing, casing slowly withdrawn as concrete level in hole rises

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● Welcome ● Contents ● Chapter 1 ● Chapter 2 ● Chapter 3 �❍ Chapter 4 ● Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Chapter 4

Drilled Shaft Equipment and Tools Contents

● This Chapter contains information on the various types of rigs and tools used in the construction of drilled shafts.

● A short quiz is provided at the end of the Chapter.

It is extremely important for the Drilled Shaft Inspector to be knowledgeable of the various types of rigs and tools used in drilled shaft construction. Though not responsible for accepting or rejecting equipment and tools, the Inspector must be able to identify these items for documenting on the daily report.

Drilled shaft construction equipment is typically divided into two categories Drilled Shaft Rigs and Drilled Shaft Tools. Following are some examples of each.

Drilled Shaft Rigs

Drilled shaft rig components, for the most part, are all essentially the same, regardless of the rig size as shown and described below.

1 - Power Unit- provides the power to turn the table & kelly

2 - Kelly- the rod running through the table that tools are attached to

3 - Table- connected to power unit, turns kelly

4 - Tool- bits, buckets, etc. that go down the hole

5 - Carrier (Crane)- carrier or main component










The rigs are typically classified by the carrier type and fall into these broad categories:

● Truck-mounted Drill Rig

Truck-mounted rigs are typically used for smaller sized holes, generally for mast arms and sign posts.

Typically these rigs excavate holes up to 5 ft. (1500 mm) in diameter to depths on the order of 30 to 35 ft. (9 to 10 m).

● Carrier-mounted Drill Rig



Carrier-mounted rigs have larger hole capabilities than the truck-mounted rigs. These generally have 2 front axles and telescoping kellys, enabling greater hole depths. Typically these rigs have the capability of drilling holes of 120 inch diameter (3000 mm) to depths ranging from 85 to 200 feet (27 to 62 m).

● Crane-mounted Drill Rig

For the largest and deepest holes, crane attachments are used. The attachments come as a unit which includes the diesel engine, transmission and torque converter. The unit is attached to the crane by using a "bridge", which provides for increased working and tool room under the table.

The hole diameter and depth capability is generally dependent upon the crane but holes 140 inches (3500 mm) in diameter to depths of near 300 feet (90-91 m) are common.

● Crawler-mounted Drill Rig

Crawler-mounted rigs offer more maneuverability and require less overhead clearance than the other rigs, making them the rig of choice for restrictive work areas.

Typically these rigs have capabilities of holes 250 feet (78 m) with diameters of 100 inches (2500 mm).



Drilled Shaft Tools

There are a variety of tools utilized by the Drilled Shaft Contractor when constructing drilled shafts. From a wide assortment of drilling bits, for rock and soil, to casing and cleanout tools, the Drilled Shaft Contractor is equipped for whatever conditions they anticipate on the project. Regardless of how powerful the rig is, if the wrong tool or poor quality tool is used, the results are not as expected. The Inspector must be able to identify these tools for documenting on the daily report.

Drilled shaft construction tools are typically divided into the following categories:

Bits

Bits are used for drilling (excavating) the shaft (hole) and can be either Auger or Barrel. Typically the Auger bits are used for soil and rock and the Barrel types used predominately for rock.Typically, the augers are turned into the material by the rig, and upon achieving penetration equal to the bit length, the auger retracted from the hole, the material removed from the flights, and the process started again

Auger Bits



Earth Auger

Earth augers, like the one shown below, are typically used in sands and cohesive materials. Earth augers are typically constructed of lighter weight material and flat

Rock Auger

Rock augers, like the one shown below, are typically used in soft to hard rock formations. Rock augers are typically constructed of heavier material than the earth augers and typically have replaceable conical or bullet teeth for cutting, rather than the flat blades associated with the earth augers. In addition, they are generally constructed with a tapered geometry.

Single flight, single cut earth auger.

Single flight, single cut rock auger.

Single Flight/Single Cut or double Flight/double Cut Augers

Single Flight/Single Cut Earth Auger Double Flight/Double Cut Earth Auger



Rock Bits

Quite often, when hard rock is encountered, auger bits cannot advance the hole and the Contractor must employ Rock Bits to drill the harder rock.

Cluster Rock Bit

This bit pulverizes the rock with many rolling bits and the cuttings are carried away through reverse circulation of the drilling slurry.

Step-face Roller Rock Bit



This bit grinds the rock up, first with the lead bit (makes small hole, but weakens outer rock). The other bits follow, gradually making the hole larger. Compressed air is used to remove the cutting with this type of bit.

Core Barrels

Core Barrels are different than Rock bits, in that the rock bits grind away the entire mass of rock in the hole, while barrels cut along the perimeter of the barrel, hence less rock cutting. When a joint or discontinuities are encountered, the core breaks off and be be removed. These are generally used where real hard rock is encountered and are often custom made for the project.

This is a single-wall rock core barrel. Note that it is equipped with replaceable bullet teeth.

This is a double-wall rock core barrel. The outer barrel does the cutting while the inner barrel remains stationary, holding the rock core in place.

Buckets

Buckets typically come in two types, Digging and Cleanout.

As the names imply, each has a designed use, one for advancing the hole, the other for cleaning the bottom of the hole. Typically, the buckets are turned by the rig, and the bottom configuration either digs up material or collects material.

Generally, the digging buckets are equipped with flat cutting teeth while the cleanout bucket has a single flat blade.



Digging Bucket

This is the type of digging bucket used in cobbles, gravel and clays.

Cleanout Bucket

When using this type of cleanout bucket, the rig is rotated in the normal drilling direction, picking up bottom sediments. Then while still on the bottom, rotated in the opposite direction, which closes the bucket, and removed from the hole.

Casing

Casing is used to maintain the stability of the hole and can be Temporary or Permanent, as discussed earlier in Chapter 3. In many instances, a short piece of casing is used at the surface (called surface casing) to prevent the surface material from collapsing into the hole and degradation of the top of the hole due to the in and out process of drilling.

Casing is typically made of strong steel and pieced together by welding to achieve the depths needed. It comes in a variety of diameters, such as 30, 36, 42, 48 inches , etc.

Temporary Casing- Temporary casing is just that, temporary. The casing is used to maintain an open hole for the construction process and is removed as the concrete is placed. This is the most common of the two casing types.

Permanent Casing- Permanent casing is just that, permanent. It is left in-place and becomes part of the drilled shaft. It is generally used when conditions, such as voids, preclude the construction without casing, as concrete placement could not be properly performed or maintained.



This picture shows a piece of casing being placed. In this picture, you can see the casing extending above existing ground and the bit being lower.

Specialty Tools

The Contractors use a number of "specialty" tools during drilled shaft construction Some of these are "homemade" and some are manufactured and used widely, such as Desanders.

Desanders, such as the one pictured above are used to remove sand from drilling slurries and maintain sand content within specified limits.

Vibratory hammers, such as the one pictured above are used in some instances to vibrate casing into the ground.



A "Belling tool" (above) is used to bell out the bottom of a hole, when specified. Lowered into the hole with the cutting blades retracted, the tool is rotated and as the cutting blades cut, the blades extend outward, excavating a "bell" shape bottom.

One of the most positive methods for cleaning the hole is a down-hole pump, such as the one pictured above. These pump the bottom of the hole sediments up and out.
















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● Welcome ● Contents ● Chapter 1 ● Chapter 2 ● Chapter 3 ● Chapter 4 �❍ Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Chapter 5

The Inspector's Role

Contents

● This Chapter contains an overview of the Inspector's main role and responsibilities during the drilled shaft construction process.


The Inspector is involved in all three phases of the project:

Pre-construction

This would involve the review of the project plans, attending pre-construction meetings and discussing, resolving, and clarifying any questions you may have. These meeting provide the opportunity for all parties to obtain a thorough understanding of the project details and goals.

The Inspector must review, know and understand the project plans.

Construction

The Inspector has numerous responsibilities during the construction phase ranging from verifying the approved equipment is on-site to determining hole cleanliness requirements have been met, just to name a few. Extremely important during this phase is the communication and coordination by the Inspector with the responsible Engineer, who must be kept informed and up to date.










The Inspector must have a thorough understanding of the specifications, special provisions, etc., the project is governed by.

Post Construction

During the post installation phase, the Inspector may be involved in documenting completed drilled shaft construction details, integrity testing and any required reports.

It is extremely important for the Drilled Shaft Inspector understand their role in the drilled shaft construction process. From participating in pre-construction meetings to documenting post installation testing, the Drilled Shaft Inspector is intimately involved and a valuable team player in achieving the results all parties goal- a quality drilled



shaft installed in accordance with the plans and specifications.

In accomplishing their duties, the Inspector's main functions are covered below:

● Serve as the Department's Representative

Each drilled shaft project is constructed based upon the approved plans and applicable specifications. The Inspector is to serve as the State's representative and ensure that this occurs.

The Contractor is entitled to be paid for their work, providing it meets the plans and specification requirements, and the Inspector, by documenting the construction, assures all parties get what is expected- The Contractor paid and the State, a quality properly installed drilled shaft.

The Inspector, serving as the "eyes and ears" of the Engineer, generally does not have, nor do they want, the authority to direct the Contractor's work.

Important keys to remember are:

Who you represent

Not to unnecessarily delay or interrupt the Contractor

Remember your common goal

● Be a "Recorder" and a "Reporter"



The Inspector must make accurate, unbiased observations of all important drilled shaft construction events. These events must be documented on the appropriate forms or reports for reporting.

Being a "Recorder" means:

Make accurate, unbiased observations- Don't record "around 2 ½ feet". Measure and record accurately- Don't record "in the PM". Put the correct time, say 2:05 PM.

Regardless of what you have heard or been told about a Contractor or who you represent, you observations are to be unbiased, based upon facts or actual observations. The Inspector inspects based upon a set of plans and specifications- it is either in accordance with or not in accordance with those documents.

Document events completely and consistently- Document events completely; this is part of your obligation to whom you represent. A half report on the volume of concrete placed or just documentation of the rig only and not the tools is unacceptable. Remember, that possibly sometime in the future, when you are on another project, someone may have questions about what occurred on your project and the only real source of information is your documentation.

Be consistent in your documentation and observations. If you start the project by recording the time it takes to drill a shaft, you need to do that on every shaft. Inconsistency draws attention and may bring your documentation into question.

Perform Your Duties Promptly- Prompt performance of your duties is imperative. You should not delay the Contractor. If the bottom of the shaft is ready for inspection, and the Inspector is not there, the Contractor is on standby.



May cost the Department money.

More importantly, if you perform your duties promptly, and an out of compliance or questionable event occurs, you can probably notify the Engineer soon enough to make a difference.

Being a "Reporter" means:

Complete Forms and Reports Accurately- Typically standard reports or forms are used, based on local practice, for the recording of drilled shaft construction activities. The Inspector should never go to the jobsite without the current forms or reports. Make sure to provide all the information requested on a form or report, accurately and completely. Incomplete or improperly completed forms or reports can call to question your documentation. As discussed earlier, also be consistent in completing of paperwork. In many locals, there are specifications regarding erasers or changes (i.e., Erasers are not permitted- make corrections by striking through the wrong entry with a single line, initial it, and write the correct entry close by). Know these, if they exist, and follow them.

Keep Forms & Reports Up-to-Date- Do not fall behind on the paperwork. Recalling from memory and deciding to scribble something down on a piece of paper for transfer later is a No, No. What is the absolute best that can happen? You get it right- everything else is a negative. Keep your paperwork current. There may arise a question on something performed the day before and if your paperwork isn't current, how can the situation be resolved.

● Keep the Engineer Informed

The Inspector serves as the eyes and ears of the Engineer. You must keep the Engineer informed so that in the event a situation arises, the Engineer is not blindsided. They are counting on you.



Therefore, it is important that the Inspector develop a rapport with the Engineer and this usually occurs during the pre-construction phase, where the Inspector and Engineer discuss specific project issuers.

Communicate- The Inspector should communicate as often as needed to keep the Engineer informed. In most instances, this is daily. The Engineer will want to know what progress was made that day, were any problems encountered, etc. Remember, they answer to someone too, who might ask them questions.

Coordinate- The Inspector should coordinate any meetings, site visit, etc., with the Engineer.

Notify the Engineer soon enough to make a Difference- As the old saying goes, "it's to late to close the gate after the horses are out". The same holds true in drilled shaft construction, only it's to late after the concrete is placed.

For example, should you observe that the cage is being constructed outside the specifications, don't wait until it is placed in the shaft, or worse yet, the concrete poured. Document, notify the Engineer right away and inform the Contractor. This will allow for the issue to be resolved before the cage is in the ground.

This type of communication can reduce the impact to the project schedule, quality and cost.








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● Welcome ● Contents ● Chapter 1 ● Chapter 2 ● Chapter 3 ● Chapter 4 ● Chapter 5 �❍ Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Chapter 6

Contractor and Equipment Arrive on Site

Contents

● This Chapter contains an overview of the drilled shaft construction from the Inspector's viewpoint and an overview of the Inspector's responsibilities during this phase of drilled shaft construction.


Just as the Contractor has their tools, the Inspector needs to have their tools also. Without the proper tools, the Inspector cannot perform their duties properly.

The Inspector should not go to the site without the "tools" discussed below.

Documents Tools

● Approved Drilled Shaft Installation Plan

● Project Plans & Specifications ● Any Special or Technical Provisions ● Required Forms/Reports

● Hard hat, boots ● Eye & ear protection ● Measuring tapes ● Scale, level, sampler ● Weighted tape (100') ● Calculator, pen, pencil ● Builders Square ● Life or reflective jacket ● Slurry testing equipment ● Concrete testing equipment

This photo shows some of the Inspector's tools, such as hard hat, field book, measuring tapes, flashlights, safety glasses,










The Drilled Shaft Construction Process

Illustrated below is the drilled shaft construction process from the Inspector's viewpoint. During each of these phases, the Inspector has specific responsibilities relating to verifying, measuring, checking, and documenting.

Because the Inspector has no specific responsibilities during the development of the Drilled Shaft Installation plan, other than to become familiar with it, and attend pre-construction meetings, as discussed earlier, we will start with "Contractor Arrives On-site".

The Contractor mobilizes to the site. They must bring the equipment specified in the accepted Drilled Shaft Installation Plan.

Excavation of the shaft begins. Typically at this stage a "Trial or Technique" shaft is constructed to determine if the methods and techniques will work.

The specified reinforcing cage is constructed and positioned in the excavation.

The specified concrete is placed into the excavation.

The specified load or integrity testing is performed to document shaft construction.



The Contractor has arrived on-site and the Inspector has some basic responsibilities to perform at this time.

These include:

● Check the Equipment ● Check for Protection

of Existing Structures

Check the Equipment

When the equipment arrives on site, it is the Inspector's responsibility to verify that the equipment brought on-site matches the equipment listed in the approved Drilled Shaft Installation Plan.

The Inspector does not have the authority to reject equipment, but must accurately document the Contractor's equipment. The equipment would have been detailed in the Contractor's Drilled Shaft Installation Plan. In some instances the Contractor may not bring the equipment or tools or brings different tools other than proposed. By documenting what equipment is on-site, should equipment related questions arise later, the Inspector's documentation serves as a record.

Some of the things to check are shown and discussed below.

Is the drill rig the specified one?

Are the bits the right type? Soil or rock; the correct diameters; single flight or double flight; single cut or double cut?



Are the buckets, barrels and other tools as listed in the approved Drilled shaft Installation Plan?

Pictured above is an Inspector checking the tremie. Tremies are to be clean and smooth on the inside.

Pictured above is the Inspector checking the dimensions of a belling tool. It needs to be in the extended position for the maximum diameter to be measured. The height needs to be measured also, to add to the kelly bar length for total depth to bottom of hole.

In this photograph the Inspector is verifying the length the casing to be used. The overall length is measured and documented.

In this photograph the Inspector is verifying the diameter of the casing to be used. He is measuring the ID and the OD, which also provides the wall thickness of the casing.

Check for Protection of Existing Structures

Some projects will be near existing structures that could possibly be damaged by the construction. Typically in these cases, the Contractor was required to submit a Protection of Existing Structures



Plan. In some instances, the construction, such as vibrating of casing in or actual drilling, can create vibrations that can impact structures in the vicinity, such as cracking of walls, etc.

Generally, the specifications will outline the requirements of the Plan and it is the Contractor's responsibility to execute that plan once approved.

It may call for surveying of potentially effected structures, within a specified distance, to document their condition prior to construction. In addition, monitoring, for vibration and/or noise may be specified, also for a specified distance, during construction.

If the project requires Protection of Existing Structures, the Inspector needs to review the approved plan and document that the Contractor is executing it.
















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Chapter 7

Shaft Excavation and Cleaning Contents

● This Chapter contains an overview of the drilled shaft construction from the Inspector's viewpoint and an overview of the Inspector's responsibilities during this phase of drilled shaft construction.


Learning Objectives

When you have completed this Chapter, you will be able to:

● Describe, in general, the Inspector's role during the shaft excavation process ● Describe, in general, the Inspector's role during the shaft cleaning process ● Determine shaft tip elevations

Trial Shaft

On most projects, the Contractor will be required to install a "Trial" shaft. In some parts of the country these are also referred to as Technique or test shafts. Regardless of the name, the purpose is the same; to determine if the method and equipment the Contractor proposed in the Drilled Shaft Plan will work. This Trial shaft will help determine critical items such as:

● Can the dry shaft construction method be used ● Can the hole be stabilized with casing ● Can the hole be stabilized with the proposed slurry ● These are just a few of the reasons for performing the trial shaft.

The Inspector's role during shaft excavation is essentially the same as for production shafts, except that typically the trial shaft will be located on the project plans a certain distance from the production shafts and the Inspector needs to verify that the shaft is performed at the specified location. Upon successful completion of the shaft, the Inspector must verify it is "finished" per the plans.

In the event, the Contractor fails to install a successful trial shaft, they must revise the Drilled Shaft Plan and attempt another trial shaft until successfully installing one that the Engineer accepts.

Shaft Excavation










The Inspector has a variety of functions to perform during the shaft excavation process. From verifying the shaft is located in the proper place to verifying the shaft meets the cleanliness requirements upon completion of excavation, the Inspector needs to document construction events.

Shaft Location and Alignment

● Is the shaft being located at the correct plan location indicated on the plans? Typically there will be a plan tolerance which the Contractor must achieve.

● Is the kelly bar plumb? This is critical as there are tolerances for axial alignment that the Contractor must achieve.

This photograph shows the Inspector checking and verifying that the shaft is in the correct plan location.



This photograph shows the Inspector and Contractor checking and verifying, on the project plans, the shaft location(s).

This photograph shows the Inspector checking the vertical alignment of the kelly.

Excavation

If the Drilled Shaft Plan specified the use of casing and or slurry, the Inspector must verify and document its use.

On many projects, a "surface casing" will be temporarily installed to stabilize the surface soils during the construction process. The constant in and out of the hole with drilling tools can quickly degrade the surface soils conditions if not protected.

The Inspector needs to be concerned with, in general, the following.

● Documenting the type of drilling tool and its diameter, and condition. Also remember to record its length, as the Inspector needs this to add to the kelly bar to determine depths.

● Documenting the length, diameter and type of any casing used. ● If slurry is used, verifying and documenting that the required sampling and testing is performed. ● Maintaining, in the required format, a log of the material excavated. Typically, there will be forms for Rock Coring, Soil/

Rock Excavation and possibly others.

Document, Document, Document.

Job site photographs are a very valuable form of documentation.



Photograph of a section of steel casing being prepared for installation by vibratory hammer. Notice the casing is "marked" in feet.

Pictured here is the Inspector examining the material on the auger that is coming out of the hole. It is important to accurately identify and document the material being excavated.

Pictured here is the Inspector checking his documentation of the shaft excavation. Notice the right-hand page is a sketch of the material identified, versus depth.

Slurry Testing

Slurry needs to be maintained properly, as discussed earlier in, if it is to be effective.

Typically, the specifications for a project will specify the type and number of tests to be performed on the slurry.

The most common tests are:

● Viscosity- also know as Marsh Funnel Test, is the test used to measure the flow rate or consistency of slurry. ● Mud Balance Test- also known as the Mud Density Test, is used to measure the density of the slurry. ● pH Test- used to determine the alkalinity and acidity of the slurry. ● Sand Content Test- used to determine the sand content of the slurry. Generally the specifications have a

maximum allowable percentage of sand permitted.

Pictured here is the Inspector pouring slurry mud into the cup of the Mud Balance Test apparatus. When filled and

Pictured here is a typical "slurry sampler".



sealed, the knife (graduated bar) is placed on the fulcrum and the sliding weight moved until the cup and arm are balanced. The density of the mud is then read from the bar.

The lower cap is lower to the desired depth and the tube then lower on the cable to that depth. The top cap is allowed to slide down thereby trapping slurry at the sample depth.

Shown here is the sand washed and collected from slurry at the final step of the Sand Content Test. The percentage of sand is read from the graduated glass vial.

Shaft Cleaning Depth Verification and Cleaning

During shaft excavation, the Inspector estimates the bottom of shaft depth by noting the depth marks on the kelly and adding the length of the particular tool to it, the sum of which provides the total depth. Upon achieving the desired shaft tip elevation and following cleaning of the shaft bottom, the Inspector needs to verify the depth and cleanliness.

Generally, cleanliness requirements will be specified and are typically based upon the amount, or thickness, of sediment permitted on the bottom of the shaft.

In making this determination, the Inspector uses a weight tape and takes "soundings" at numerous locations (normally 5) around and in the center of the shaft. These are recorded on the specified form. This should be done as soon as possible, as the longer the hole is open, the greater the potential for problems.

Pictured here is the Inspector "sounding" the shaft for depth



and cleanliness.

Pictured here is a typical "weighted" tape used to measure shaft depth.

Illustrated below is a typical 5 location sounding pattern to check for depth and cleanliness.

Determining Tip Elevation

The Designer has designed the drilled shaft foundations based upon a variety of factors and their design is based upon a certain shaft diameter and depth of penetration below existing ground surface. Where the bottom of the shaft is to be located is referred to as the "shaft tip elevation".

This elevation is determined from a fixed point elevation provided by the Contractor. Typically, this is the top of casing or some other fixed reference. Using this elevation and the depth measured on the kelly or weighted tape, the Inspector calculates the



shaft tip elevation, to verify the Contractor is at the specified elevation.

To determine the shaft tip elevation merely subtract the depth (in feet or meters) of the shaft below the reference elevation from the reference elevation.

Remember to watch for + and - elevations.

EXAMPLE:

1. Reference Elevation = + 135.75 feet

Depth to bottom of Shaft = 55.0 feet

+135.75' - 55.0' = Shaft Tip Elev. of + 80.75 feet

2. Reference Elevation = + 25.75 feet

Depth to bottom of Shaft = 55.0 feet

+25.75' - 55.0' = Shaft Tip Elev. of - 29.25 feet
















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Chapter 8

Rebar Cage Fabrication and Positioning

Contents

● This Chapter contains an overview of the fabrication and positioning, in the hole, of the rebar cage and an overview of the Inspector's responsibilities during this phase of drilled shaft construction.


Learning Objectives


● Describe, in general, the Inspector's role during the rebar fabrication and positioning process ● Determine the circumference of the shaft and cage

Rebar Cage

Drilled shaft foundations are constructed with a rebar cage inside to provide for strength and stability. The rebar cages are constructed to meet the needs of the design, both in rebar size and number required.

The Inspector must verify that the cages are fabricated, lifted and positioned properly and are within the allowable tolerances for "top of cage elevation" after positioning.

Quite often, post installation integrity testing will be specified and the access tubes for performing these test are part of the cage assembly.

Remember, it is imperative that the hole be clean and this should have been verified by the Inspector before the rebar cage is installed.










Cage Fabrication

The Inspector must verify that the cages are constructed in accordance with the plans and specifications, which includes verification of:

● Bar size ● Number of bars and condition ● Type and percentage of ties ● Diameter and length ● Couplers/splices ● Spacers and Standoff

Shown here is the cage under construction. The workers are tying the cage together. The angled piece of bar is a stiffener, to help maintain the cage shape.

The Inspector verifying the cage diameter by measuring with a tape.

Here the Inspector is checking the ties for compliance to the plans. Typically, the plans will specify a

certain percentage of the intersections be tied.



Cage Lifting and Positioning

Following fabrication of the cage, the Contractor will then lift the cage and lower it into the shaft.

Remember that prior to cage placement the Inspector verified the shaft depth and cleanliness.

It is important that the Contractor properly support the cage during lifting to avoid bending the cage so much that it is permanently distorted. If distorted to much, it won't fit down the shaft without damaging the shaft walls.

Typically the cage will have standoffs on the bottom to maintain a certain clearance from the bottom of the hole and spacers on the outer edges to maintain a specified distance from the shaft walls.

This space between the shaft walls and the cage is to provide for the specified "concrete coverage".

Once positioned in the shaft, the top of the cage is to be within a specified tolerance of the elevations shown in the plans.

In summary, the Inspector needs to verify and document:

● Lifting of the cage ● Positioning of the cage ● Top of cage elevation ● Couplers/splices

The photograph above shows the Inspector observing the lifting of the cage and the photo to the right, a cage lifted and ready to be placed in the hole.



This photograph shows the cage being lowered into the hole. Notice that the standoffs and the side spacers are used to maintain the proper "coverage".

Here is a photograph of the cage after being positioned in the hole. The Inspector needs to verify and document the "top of cage" elevation and if it is within the specified allowable construction tolerance.

Access Tubes

Post installation integrity testing of drilled shafts has become very popular throughout the country. More economical than conventional load tests, some of the methods used provide a "picture" so to speak of the shaft in the ground.

To perform these types of test, access tubes, which permit lowering of instrumentation down into the shaft, must be installed on the cage prior to placing the cage in the hole.

The Inspector must verify and document that the tubes are of the length, diameter, and material specified, together with verifying they are secured to the cage and straight in accordance with the the project plans.

Shown here is an access tube inside the cage. Normally, they are installed on the inside of the cage, which helps protect them from damage.

Note the cap on the tube- this prevents debris or concrete from getting into the tube, which can prevent the instrumentation from going down the tubes.



This photograph shows the access tubes installed on the outside of the cage. Care must be taken by the Contractor when placing the cage to avoid damage to the tubes.

Determining Circumferences

Determining circumferences is one of the math computations the Inspector must be proficient in performing.

Typically the number of side spacers that help maintain the proper coverage distance, as discussed earlier in this Chapter, are generally determined by the cage circumference. The plans or specifications will typically indicate a certain number of spacers, based upon inches of circumference of the cage, be placed per level.

Circumference is the length of the outer boundary (perimeter) of a circular object.

To determine the circumference of a circular area, such as a drilled shaft or rebar cage;




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● Welcome ● Contents ● Chapter 1 ● Chapter 2 ● Chapter 3 ● Chapter 4 ● Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 �❍ Chapter 9 ● Chapter 10 ● Glossary ● Inspector math

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Chapter 9

Concrete Operations Contents

● This Chapter contains an overview of the concreting of the shaft following rebar cage installation and an overview of the Inspector's responsibilities during this phase of drilled shaft construction


Learning Objectives


● Describe, in general, the Inspector's role during the placement of concrete ● Describe, in general, the concrete placement methods and process ● Determine theoretical shaft concrete volumes and develop placed concrete volume curves

Concreting Operations

Concreting of the shaft is the final step in the construction process itself. Up until this time, the Contractor has been willing to spend time with the Inspector but often this changes once the concrete is on the way. There are generally time limits, slump requirements, etc., a whole host of issues or potential problems that can occur during this phase. Remember, if concreting goes bad, the shaft is lost and everything the Contractor has done up until this point is essentially lost.

The Inspector needs to perform their duties promptly and efficiently. Speed is of the essence, but do not sacrifice quality and thoroughness.These duties may, depending upon the specifications, include performing standard field concrete tests, monitoring concrete placement and development of the placement curves.

Pictured here is the arrival of the concrete truck. Depending upon the specifications, the Inspector may have concrete sampling and testing to do in addition to placement monitoring.

Concrete Type and Slump










When the concrete arrives on-site, the Inspector may be required to verify the proper mix design is being delivered, that it meets the slump requirements and perform standard field tests. Typically there will be a time limit imposed by the specifications relating to the length of time for concrete placement.

Remember, it is imperative that the hole be clean and this should have been verified by the Inspector before the rebar cage was installed.

Typical concrete field tests the Inspector may be required to perform include:

● Slump ● Air Content ● Temperature ● Test Specimens

Shown above is the typical slumps specified for drilled shaft concrete.

The slump to the left is OK for drilled shafts. Notice the concrete is plastic, not like the one pictured to the right, where the slump is Ok but the concrete not plastic as the segregation of the concrete is visible.



The photo to the left shows a concrete with too low of a slump. Would be difficult to pump or place through a tremie.

Concrete Placement Methods

A variety of methods or techniques are used by the Contractor to place the concrete. This selection generally depends upon the type of shaft construction being used and the most common one.

Tremie Placement - Gravity-fed tremie placement is generally used for wet shaft construction. In this method, the concrete is introduced into the hole, starting at the bottom, using a water tight tremie (tube). The concrete is fed by pump or bucket into the tremie and falls by gravity and continuously placed until the shaft is full.

Pump-line Placement - This method is similar to the tremie method except that the concrete is "pumped" into the hole, rather than gravity fed. (A pump-line can be used to feed concrete to a tremie in tremie placement).

Free-Fall - In this method, the concrete is placed by free-falling from the top of the shaft to the bottom and is typically used for dry shaft or dry cased shaft construction only. Of importance with this method is that the concrete must be directed to free-fall down the center of the cage and not make contact with the cage or shaft walls. The specifications will often specify the maximum distance concrete may free-fall.

Pictured here is a tremie, with a hopper on top, placed in the shaft for concrete placement.

Pictured here is the pump-line method in use.

This picture shows concrete being placed by the free-fall method.



Concrete Placement Process

The goal of concrete placement is to get the shaft filled with the specified concrete and have no voids or sediment/debris inclusions that effect the structural integrity of the shaft.

During placement by tremie or pump-line, the discharge end is placed near the bottom of the hole and concrete flow started. The concrete, as it rises and fills the shaft, displaces the sediments.

During the pour, whether by tremie or pump-line, the concrete flow must be continuous and the discharge end of tremie or pump-line must be immersed in the concrete a specified distance, typically 5 ft. (1.5 m). If not, and the discharge end breaches (raised above the concrete flow level) the shaft is rejected. The tremie is raised as the concrete level rises, but the required immersion distance maintained.

The placement continues until fresh concrete overflows the top of the shaft.

In this picture, the Inspector is checking the tremie, for material, leaks, etc.

This is a picture of concrete overflowing the shaft.

This picture is looking down inside a cased shaft with the concrete being place by the pump-line method.

Concrete Volumes

So, how much concrete should go into this hole and how do we know if sufficient concrete is being placed? The drilled shaft Inspector deals with two concrete volumes, the theoretical and the actual.

Theoretically, the drilled shaft should take "x" cubic yards or cubic meters of concrete. By calculating the volume of the shaft, we can arrive at "x".

The actual must be determined during the actual placement. By comparing the actual, as it is placed, to the theoretical, the Inspector can get a "feel" for what is happening below the ground surface. For example, if your gas tank was registering empty and holds 16 gallons, but when you gas up you can only get 10 gallons in it, something is wrong. Something is taking up space in the tank or it has collapsed some, assuming the gauge works.On the other hand, you reach 16 gallons, then 18, then 20 gallons, it is probably leaking.

These illustrations show how this relates to a drilled shaft.



With this shape, you would expect the theoretical and actual volumes to be quite close.

But, what if the shaft looked like this below ground surface?

This subject, due to its complexity, is covered in detail in the Drilled Shaft Inspector course.

So, based upon these illustrations, we know that if we compare the actual to the theoretical volumes, during placement, we'll have a feeling for what is happening below ground. This is done with the Concrete Volume Curves.

This is a large part of the Inspector's duties during concreting. The Inspector prepares the Concrete Volume graph, calculates the theoretical and plots it. Then, during concrete placement, the Inspector determines the volume of concrete placed after each load, plots these values, which forms a plot relative to the theoretical.

Theoretical Volume - To calculate the theoretical volume of the shaft:

To obtain the actual volumes, the Inspector needs some basic information such as the volume per truck, the depth in the hole to the top of concrete


http://www.fhwa.dot.gov/infrastructure/tccc/tutorial/shafts/text.htm#9volume_example


following each load and the elevation of the top of concrete after each load.

This is best collected in a table form, much like illustrated below. The elevation at the top of cumulative concrete amount after each load is plotted at the corresponding top of concrete elevation.

The plot of the concrete volume curves is typically performed on a provided inspection form. Illustrated below is how the data and curves are developed based upon the collected data.

First the Elevation and Cumulative Volume axis are labeled. Make sure the graph (see graph below) is labeled to include the bottom of shaft and top of shaft elevations and the total cumulative cubic yards.

Next plot the theoretical volume. Plot the Bottom of Shaft elevation at 0 yards and the theoretical volume at the the corresponding Top of Shaft Elevation.

Next plot each cumulative total at the corresponding elevations starting with 0 at the bottom of shaft elevation. Draw in the plot.

Actual plots that:


http://www.fhwa.dot.gov/infrastructure/tccc/tutorial/shafts/text.htm#9table_form

http://www.fhwa.dot.gov/infrastructure/tccc/tutorial/shafts/text.htm#9table_form_example


Parallel the theoretical generally OK

Move away from theoretical generally OK

Cross over or move back towards theoretical generally indicate a problem.

I you have completed Chapter 9 and am ready to take the Quiz















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Chapter 10

Post Installation Integrity Testing Contents

● This Chapter contains an overview of the post installation integrity testing methods. ● A short quiz is provided at the end of the Chapter.

Learning Objectives


● Identify and describe, in general, the various post installation integrity and load tests

Now the shaft is in, we need to ascertain its structural integrity. Will it carry the load it was designed for? Are there defects within the shaft caused by errors in construction?

There are two basic methods to test shafts, those being:

● Load Tests - these are test to determine if the shaft, as constructed, will carry the loads designed for. ● Integrity Tests - these are tests to evaluate the soundness or "integrity" of the constructed shaft.

Typically the Inspector is not involved in these post installation tests, except to document they have been completed. However, in some instances, the specifications may require some involvement.










Load Tests

Load tests come in several different types, which are used to determine different load carrying or resistance capacity. The three typically methods of load tests are:

Axial load tests - tests to determine if the shaft can carry the load imposed without settling.

Lateral load tests - these are test that test the shafts resistance to lateral forces.

Uplift tests - these tests are the opposite of axial, in that rather than push downward on the shaft, it is pulled upward to determine its resistance to being "pulled out".

Pictured above is a Statnamic Load test being performed on a shaft for a new bridge.

Pictured here is a lateral load test on a shaft to verify ship-impact capacity.

In these tests, reaction loads are jacked against, applying loads incrementally, and the movement measured and documented.

For axial, the load is applied downward. For lateral tests, the load is applied from the side. For uplift, the load is applied upward, as in pulled.

Some of the more common tests used are Static Load Test, Statnamic Load test and Osterberg Load test.

Static Load Test



The photo above is of a typical, simple arrangement for loading a drilled shaft laterally. Two companion shafts are used to support the load from the reaction beam. The test shaft is pushed away from the reaction shafts, not pulled toward them (which might produce excessive stress overlaps in the soil). In a conventional test, shown at the right, reaction (anchor) shafts are installed on either side of the test shaft (two or four can be used). The anchor shafts should normally be constructed first. Hydraulic jacks are placed on top of the test shaft, usually on a steel plate that is carefully leveled. A reaction frame spans the anchor shafts, as shown. Potential disadvantages of this method are that it is relatively expensive compared to the other methods and the capacity is limited because of the use of the reaction frame. The conventional method can also be used to conduct uplift, or "pullout" test.

In a conventional test, shown above, reaction (anchor) shafts are installed on either side of the test shaft (two or four can be used). The anchor shafts should normally be constructed first. Hydraulic jacks are placed on top of the test shaft, usually on a steel plate that is carefully leveled. A reaction frame spans the anchor shafts, as shown. Potential disadvantages of this method are that it is relatively expensive compared to the other methods and the capacity is limited because of the use of the reaction frame. The conventional method can also be used to conduct uplift, or "pullout" test.

Statnamic Load Test



An alternate way of testing drilled shafts is the Statnamic® test method. The principle of operation is shown to the right. Heavy masses on top of the shaft are accelerated upward by a propellant. This produces a force against the masses equal to the mass of the accelerated masses time the magnitude of the acceleration and an equal and opposite force on the top of the shaft. On the lower right is a photo of a Statnamic test being performed.

Pictured above are the reaction weights (rings) and the propellant (charge) for a Statnamic Test.

Pictured to the right is a Statnamic Test just after the charge was setoff. The rings, which are now above the casing were originally set even with the top

of the casing Osterberg Load Cell

In the Osterberg Cell method the cell must be cast into the shaft at the time of construction, which means that the shafts to be tested must be identified in advance, unlike the Static or Statnamic.



Shown above is the principle of the operation of the Osterberg Cell. The Osterberg Cell rests on top of the reaction socket. Other configurations can be used to test end bearing only or to test both end bearing and side resistance.

This photo shows one 3000-ton cell being used to test a socket in soft rock. The socket diameter is 60 inches, so the 2-inch steel plates on either side of the Osterberg Cell are 59 inches in diameter. In this case the objective of the test was to find the ultimate side shearing resistance in the soft rock.

Integrity Tests

Just as Load tests come in several different types, so do Integrity tests. Most are non-destructive and are used to identify anomalies or defects in installed shafts.

Performing Sonic Echo test. Larger hammers, such as in this case, are used for deeper tests

Very large defect in shaft found by Sonic Echo test.

The most commonly used Integrity Tests are:

Sonic Echo / Impulse-response- test is performed on installed shaft- quick, easy and inexpensive.



Above is a schematic of a pulse-echo (sonic-echo) test. The principle is obvious from the sketch. Advantages of the test are that it can be done on virtually any shaft without prior planning (no access tubes need be placed in the shaft) and is quick and inexpensive. Disadvantages are that it is prone to showing false positives and to missing fairly large voids or inclusions in the concrete. It is essentially 100 per cent accurate only if the void or inclusion covers about half of the cross-sectional area of the shaft and is reasonably thick (say 18 inches (0.5 m) or thicker) and the test is performed correctly. This test is not usually effective in locating deep defects (depth > 60 feet (20 m) and cannot detect contact problems between the concrete and the soil or rock. False positives in this method come from changes in cross-section that are not associated with an anomaly, from changes in concrete modulus (such as at the interface between concrete placed from two different trucks), from changes in the stiffness of the soil or rock surrounding the shaft, which also dissipate sonic energy, and from testing technique errors such as setting the sensor on weak or powdery concrete.

Sonic Echo test being performed on a shaft over water. Note the small hammer being used to strike the shaft.

Cross-hole Acoustic (CSL) - these are test are performed in the access tubes installed on the rebar cage and is much more accurate than Sonic Echo testing.

A primary use of access tubes is in the performance of cross-hole acoustic tests (usually ultrasonic in air but sonic in concrete), sometimes called cross-hole sonic log tests or CSL tests. "Shots" are made from a source that generates acoustic energy to an energy receiver in another tube at the same elevation, as depicted to the right. Both the time of travel from the source tube to the receiver tube and the amount of energy transferred between tubes are indicators of the presence of either sound concrete or defective concrete. Good coverage of the interior of the cage can usually be achieved, however, little information on concrete outside the cage can be obtained.

Several variations on this method are practiced by highly skilled specialists, involving placing source and receiver at different elevations to develop a three-dimensional profile of the interior of the shaft, in a process referred to as tomography.



This method can be performed fairly quickly and is often more definitive than the pulse-echo method. However, as mentioned above, shafts to be tested must be identified in advance of construction to permit installation of the access tubes.

Sensors used in performing the CSL test.

Gamma-Gamma - these tests are also performed in access tubes with a nuclear density instrument. This test is also more definitive than the Sonic Echo test.

Another successful down-tube integrity test is the gamma-gamma, or backscatter gamma test, illustrated to the right. The device is a nuclear density meter that must be calibrated frequently. It measures density in the concrete to about 100 mm (4 inches) from the edge of the tube. Newer devices can reportedly measure density to about twelve inches from the tube, but that characteristic is of little use if the tube is less than twelve inches from the edge of the shaft. A disadvantage of the device is that it does not "shoot" across the shaft as does a CSL device, so it does not test the entire cross-section, and it is sensitive to being placed too close to a longitudinal rebar. Otherwise, it is a very definitive test.

This, like the CSL tests, requires advance identified of the shafts to be tested to allow for access tube installation.

Nuclear density source being lowered into access tube for gamma-gamma testing.



Coring - this is the most destructive of the common tests as a drill rig cores the shaft and the retrieved concrete cores are examined. This can be performed on any shaft and does nor require pre-installed instrumentation.

Coring of drilled shafts can be used as an independent integrity test method, or it can be used to attempt to confirm the presence of defects that appear as anomalies on pulse-echo records.

Coring is performed by setting a drill rig over the finished shaft, and then performing continuous core runs, typically 5 ft. (1.5 m) in length, to the bottom of the shaft. The individually retrieved cores are then set out, end to end, which gives a picture of the shaft concrete, etc.

The bottom left picture is an unacceptable shaft, based upon coring results and the bottom right picture is an acceptable shaft. Notice how the cores from the acceptable shaft are more intact and solid.

Coring is not full-proof, however, as cores can bypass serious defects. So, coring is a way of potentially confirming that the shaft is defective but not that it is not defective.

Very careful coring is sometimes an effective way to investigate whether there is a soft base in the drilled shaft.

Unacceptable

Acceptable

I you have completed Chapter 10 and am ready to take the Quiz













Drilled Shaft Tutorial Glossary


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● Welcome ● Contents ● Chapter 1 ● Chapter 2 ● Chapter 3 ● Chapter 4 ● Chapter 5 ● Chapter 6 ● Chapter 7 ● Chapter 8 ● Chapter 9 ● Chapter 10 �❍ Glossary ● Inspector math

tip sheet

Appendix A

Glossary

Adhesion The property of a

substance (in our case, cohesive soil) to "stick", "cling", or "adhere" to a solid structural element such as a concrete pier or pile, and thus establish a resistance to shearing movement between the soil mass and the structural element.

ADSC Association of Drilled Shaft Contractors (The International Association of Foundation Drilling Contractors), Address P. O. Box 75228, Dallas, TX 75228.

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Aggregate The stone used in making concrete. "Fine aggregate" is sand; "coarse aggregate", gravel or gravel-size crushed stone.

Air Lift A device used to clean material from the bottom of a fluid-filled shaft, usually constructed using an open-ended steel pipe into which compressed air is injected near the bottom in an upward direction.

Allowable Load The load which cannot be exceeded without incurring (in the opinion of the designer) risk of damaging structural movement.

Anchor Pier A pier designed to resist uplift or lateral forces



Artesian Water Subsurface water underlying a confining bed which has sufficient pressure to rise above existing ground (or water surface) when encountered in cased holes during drilling.

Attapulgite A clay mineral consisting of complex magnesium aluminum silicates. It occurs naturally near Attapulgus, Georgia where it is mined as Fuller's earth. Also made into commercial drilling mud useful in salt or brackish water environments.

ASTM American Society for Testing and Materials

Auger A helical rotary tool for drilling a cylindrical hole in soil and/or rock.

Axial Load That portion of the load on a pier or pile which is in the direction of its axis.



Backfil A bucket-like tool for removing water from the hole during drilling or in preparation for concrete placement.

Bailing Bucket A bucket-like tool for removing water from the hole during drilling or in preparation for concrete placement.

Batter Angle with the vertical, normally expressed as a ratio of horizontal to vertical (i.e., 1:4= 1 horizontal to 4 vertical).

Bearing Stratum A soil or rock stratum that is expected to carry the drilled shaft load (either by end bearing or by sidewall friction, or by a combination of the two).

Bell Enlargement of the lower end of a shaft excavation, to increase the bearing area of the drilled shaft (Also called "underream").



Belling Bucket Underreaming Bucket

A drilling bucket tool with expanding cutters that can enlarge the bottom of the drilled hole, to form a bell or underream. See Bucket Auger, Drilling Bucket.

Bentonite The mineral, sodium montmorillonite, a highly expansive colloidal clay; the basis for a type of commercial

Boulder A rock, usually rounded by weathering and abrasion, greater than 200 mm in size.

Bucket Auger (or Drilling Bucket)

A cylindrical rotary drilling tool with a hinged bottom containing a soil cutting blade; spoil enters the "bucket" and is lifted out of the hole, swung aside, and dumped by releasing the latch on the hinged bottom.

Cage Reinforcing bars preassembled for quick placing in a drilled shaft.



Cake (Filter Cake) A layer of clay or clayey soil, built up on the wall of a boring drilled with slurry (drilling mud, bentonite, etc.), having the effect of forming an impermeable lining to prevent (or diminish) loss of water from the hole, and maintain slurry pressure against the wall of the hole.

Calcarenite Mechanically deposited carbonate rocks consisting of sand size carbonate grains (1/16 to 2 mm diameter)

Calcilutite Refers to a rock composed of more than 50% silt and clay size carbonate particles.

Calyx (or Shot) Barrel A core barrel without hard-metal cutting teeth, with which the rock is cut (or ground up) by chilled steel shot which roll and are ground up under the rotating steel edge of the barrel.



Capillarity The upward movement of water, due to effects of wetting and surface tension, that occurs through the very small void spaces that exist in a soil mass.

Carbonate Rocks Rocks composed of more than 50% by weight, of carbonate minerals.

Casing An open-end steel pipe installed by drilling, driving or vibrating; to support the wall of a hole; to seal out groundwater; or to protect the concrete of the shaft from contamination by sloughing of the sides of the hole.

Caving (or Sloughing) A soil that tends to fall into an uncased hole, during or after the drilling. Usually a cohesionless soil.



Changed Conditions Job conditions, which differ, substantially from conditions as represented in the plans and specifications, and/or the contract documents.

Chert A hard, dense microcrystaline sedimentary rock, consisting chiefly of interlocking crystals of quartz. It may contain amorphous silica (opal). Chert occurs principally as nodular or concretionary segregations, or nodules, in limestone and dolomite, and less commonly as layered deposits, or bedded chert. The term flint is equally synonymous.

Clay A mineral particle of any composition having a diameter less than 0.002 mm.



Cleanout Bucket A cylindrical tool used for removing "cuttings" from the shaft bottom. The bucket typically has a bottom that opens up when turned clockwise and closes when turned counterclockwise.

Coarse-Grained Soil The soil types which have particles large enough to be seen without magnification. The coarse-grained soils include the sand and gravel (or larger) soil particles.

Cohesion The bonding or attraction between particles of certain fine-grained soils that enhances shear strength and is independent of confining pressure.

Cold Joint Surface where concrete placement was interrupted then later resumed.



Concrete Pump A truck mounted pump specially designed to transfer fluid concrete through lines (hoses and pipes) to deliver ready mix to locations not readily accessible otherwise.

Continuous Flight Auger A string of helical augers and a cutting head, used to bore a hole in the earth, into which a pile section may be set, concrete cast in place, or tieback grouted.

Coquina A soft, porous limestone made up largely of shells, coral, and fossils cemented together.

Core Barrel A cylindrical rock-drilling tool, designed to cut an annular space around a central cylindrical core of rock, which can then be removed to classify the material or in the case of a drilled shaft removed to deepen the hole.



Crane Carrier A specially built truck for mounting a drill rig or for carrying a crane.

Crowd The soil types which have particles large enough to be seen without magnification. The coarse-grained soils include the sand and gravel (or larger) soil particles.

Cuttings Particles of soil or rock resulting from the cutting action of drilling or augering a hole. See also Spoil.

Dense Compact

Desander A specially designed piece of equipment consisting of a series of screens and hydrocyclones which remove sand and silt particles from the slurry used in constructing a fluid-filled excavation.



Dewatering (1) The removal of water from a construction area, as by pumping from an excavation or location where water covers the planned working surface. (2) Lowering of the groundwater table in order to obtain a "dry" area in the vicinity of an excavation which would otherwise extend below water.

Diatomaceous Earths Silts containing large amounts of diatoms-the siliceous skeletons of minute marine or freshwater organisms

Dolomite A carbonate rock composed of more than 50% by weight, of the mineral dolomite.

Drawdown Lowering of the level of groundwater; for example, when a work area is dewatered for construction.



Downdrag A downward force exerted on a drilled shaft, pile, or other structural element by settling soil. Sometimes called "negative skin friction".

Drilled Pier/Drilled Shaft A reinforced or unreinforced concrete foundation element formed by drilling a hole in the earth and filling it with concrete. Also called a "caisson", or a "large-diameter bored pile".

Drilling Bucket A closed rotary boring tool with its cutting edge at its base. Spoil is removed from the bucket by lifting it out, swinging it to one side of the hole, and releasing the hinged bottom of the bucket.

Drilling Mud, Mud, or Slurry A fluid mixture of water and clayey soil, or commercial "driller's mud" which may be bentonite or attapulgite.

Elastic Movement Movement under load which is recoverable when the load is removed.



"Elephant's Trunk" A collapsible conduit of fabric or plastic which, when coupled to the bottom of a concrete hopper, directs the concrete to a point near the center of the reinforcing cage to prevent concrete from striking the cage or the sides of the shaft.

End Bearing The portion of load carrying capacity a shaft or pile has due to the end area bearing on the material below.

Extractor A device for pulling piles or casings out of the ground. It may be an inverted steam or air hammer with yoke so equipped as to transmit upward blows to the pile body, or a specially built extractor utilizing this principle. Vibratory hammers/extractors may be especially effective.



Fill Any man-made soil deposit. Fills may consist of soils that are free of organic matter and that are carefully compacted to form an extremely dense, incompressible mass, or they may be heterogeneous accumulations of rubbish and debris.

Fine-Grained Refers to silt and clay-sized particles which exist in a soil.

Fixed-Head Pier A pier whose top, when deflected laterally with application of lateral force, is so restrained that the pier axis at the top must remain vertical during such movement.

Friction/End-bearing Pier A pier that achieves support from the combination of side friction and tip (end) bearing.



Friction Shaft A pier that derives its resistance to load by the friction or bond developed between the side surface of the pier and the soil or rock through which it is placed.

Fuller's Earth Soils having the ability to absorb fats or dyes. They are usually highly plastic, sedimentary clays.

Full-Scale Load Test A load test made on a full-scale shaft or other structural element, with the load carried at least to the structural design load, and preferable to twice (or more) the design load.

Geomaterial Material (soils, rock, clays, silts, etc.) underlying the surface.

Geotechnical Engineer An engineer with specialized training and knowledge of structural behavior of soil and rocks, employed to do soil investigations, to do design of structure foundations, and to provide field



observation of foundation investigation and foundation construction.

Grains Discrete particles larger than 0.074 mm. They may form the rock framework, similar to sand grains in a sandstone, or they may be subordinate to smaller particles in the rock.

Grain Size A term relating to the size of grains. (See above)

Gravel Small stones or fragments of stone or very small pebbles larger than the particles of sand, but often mixed with them. Generally 4.76 to 75mm in size. (Stones 75 to 300 mm are usually called "cobbles".



Ground Loss Subsidence of surface of ground adjacent or close to a shaft excavation, caused by soil moving into the excavation laterally during drilling, or during dewatering after drilling is complete. Common in soft organic soils or clays, and cohesionless soils below the water table.

Groundwater Level A shallow pit, excavated adjacent to a boring location, used to contain drilling mud (slurry) during drilling.

Hardpan A term that should be avoided by the engineer. Originally, it was applied only to a soil horizon that had become rocklike because of the accumulation of cementing minerals. The name implies a condition rather than a type of soil.



Head Shortened form of the phrase "pressure head", referring to the pressure resulting from a column of water or elevated supply of water.

Hollow-Stem Auger An earth auger with an end bit on a hollow center shaft.

Hydraulic Pump The hydraulic pump is the same and performs the same functions as the electric submersible pump except it is hydraulic.

Impervious Impervious soil is soil in which the spacing of the soil particles is so close as to allow only very slow passage of water. For example, movement of water through a typical clay (an "impervious" soil) may be only 1/1,000,000 as fast as through a typical sand.



Kelly bar (or Kelly) The kelly bar transfers the rotary and pull-down force to the drilling tools. The kelly bar is also used to raise and lower the tools in the shaft. It may be solid or hollow with two or more bars telescoping inside each other. The ability of the bar to telescope, allows excavation to greater depths than the boom height would otherwise allow.

Laitance A fluid mixture of water, cement, and fine sand that appears at the top of concrete soon after pouring

Lateral Load That portion of load that is horizontal, or at 90E to the axis of a pier or pile, or of the supported structure.

Limestone A carbonate rock composed of more than 50%, by weight, of the mineral calcite.



Load Cell A device for measuring the pressure exerted between the soil (or rock) and a structural element (e.g., the bottom or side of a pier); used with a hydraulic or electrical indicating or recording instrument at ground surface.

Matrix The natural material in which any fossil, pebble, crystal, etc., is embedded.

Micrograined A grain-size term pertaining to carbonate particles smaller than 0.0625 mm and larger than .004 mm diameter.

Mud See Drilling Mud

Mud Pit A shallow pit, excavated adjacent to a boring location, used to contain drilling mud (slurry) during drilling.



Mudding-In The technique of stirring soil and water by and auger; sometimes with the addition of commercial "driller's mud", to form a slurry as the hole is advanced by auger drilling.

MultipleUnderreams Additional underream cut in a bearing soil, at elevations above the bottom underream, to force shearing resistance in the soil into a larger peripheral surface.

Moisture Content The reduction in diameter in a section of a drilled shaft.

Natural Moisture Content Moisture content in-situ, at the time of measurement or investigation. May be subject to seasonal variation

Necking The reduction in diameter in a section of a drilled shaft.



Negative Skin Friction Effect of settling soil that grips a pile or pier by friction and adds its weight to the structure load. Also called Downdrag.

NX Core Rock core taken with an "NX" core barrel, which cuts a core 60mm in diameter.

Oolite Small spherical or subspherical carbonate accretionary grain generally less than 2.0 mm in diameter.

Over Reaming Enlarging the diameter of the shaft to remove any slurry cake build up

Piezometric Head (See Artesian Pressure)

Plasticity Term applied to fine-grained soils (such as slays) which when moist can be remolded without raveling or breaking apart.

Rebar A bar of reinforcing steel.



Reverse Circulation A counterflow method of circulating drilling fluid and spoil in a drill hole. In the direct circulation method, drilling fluid is pumped down a hollow drill pipe, through the drill bit, and back to the surface in the annular space around the drill pipe; and the cuttings are carried to the surface by the flow. In the reverse-circulation or counterflow system, drilling fluid is pumped out of the drill stem at the top circulated through a pit where cuttings are removed, and returned to the annular space around the drill stem. Circulation is upward inside the drill stem and downward outside it.

Rig, Drilling Rig A machine for drilling holes in earth or rock.



Rock A naturally occurring mineral substance cohesively bound by chemical bonds and forming the basic structure of the earth's crust.

Rock Auger An auger-type drilling tool, equipped with hard-metal teeth to enable it to drill in soft or weathered rock.

Rock Socket That portion of a shaft, which penetrates into a rock formation beneath less competent overburden.

Rotary Boring A method of boring using rotary (as opposed to percussive) means of excavation.

Rotary Drill Rig A rotary drilling machine powered hydraulically, pneumatically, electrically or mechanically to bore exploratory holes or for installation of drilled shafts, caissons, or in-situ piles. The equipment may use a continuous-



flight auger or a rotary table and Kelly bar with various attachments and tools to perform the work.

Sand Cohesionless soil whose particle sizes range between 0.074 and 4.76 mm in diameter.

Seepage Small quantities of water percolating through a soil deposit or soil structure.

Segregation Separation of poured concrete into zones of coarse aggregate without fines, and sand-water-cement without coarse aggregate.

Settlement (1) The amount of downward movement of the foundation of a structure or a part of a structure, under conditions of applied loading. (2) The downward vertical movement experienced by structures or soil surface as the underlying supporting earth compresses.



Shaft Inspection Device (S.I.D.)

The shaft inspection device is an instrument that allows the inspector to see the bottom of the drilled shaft. It has a video camera that is lowered to the bottom of the drilled shaft. It can also measure the thickness of sediment on the bottom of the shaft and sample sidewall soils.

Sidewall Grooving The cutting of circular or spiral grooves in the walls of a drilled shaft hole in rock or soil, with the objective of improving sidewall support.

Sidewall Shear Frictional resistance to axial movement of a pier or pile, developed between the soils surrounding the shaft and the peripheral surface of the shaft. (Does not include resistance to movement of an enlarged base, due to development of shearing strains within the soil below the base).



Silt A fine-grained nonplastic soil; often mistaken for clay, but quite different in its behavior. (Particle sizes ranging from 0.002 to 0.074 mm).

Skin Friction Resistance to shearing motion between the concrete of the shaft and the soil or rock in contact with it.

Slurry See Drilling Mud

Soil Auger The soil auger is used for cutting and removing the soil from the shaft volume. It typically has several flights of 30 degrees or less.

Sonotube A cylindrical form of treated cardboard, for forming round columns of concrete; a commercial product



Spacers Spacers are used to keep the steel cage centered in the drilled shaft and insure proper concrete cover. The spacers should be concrete wheels o other approved non-corrosive spacing.

Spoil Soil or rock removed from an excavation; to be wasted or used elsewhere as fill.

Squeezing Ground A soil formation, usually of clay, silt, or organic material, which tends to bulge or squeeze into the hole during drilling, or afterward if the hole is left uncased.

Standard Penetration Test (SPT) (N)

The number of blows required to drive a 2-inch O.D., 1-3/8 inch I.D., 24-inch long, split soil sampling "spoon" 1 foot with a 140 pound weight freely falling 30 inches. The count is recorded for each of three 6-inch increments. The sum of the second and third increments is taken as the N value



in blows per foot. (This is ASTM Designation D 1586).

Strain Gauge An instrument or device for measuring relative motion (compression, elongation, or shear) between two points in a mechanism or in a structural member such as a drilled shaft

Swelling Soil A soil subject to volume increase caused by wetting, oxidation, buildup of crystals, or relaxation after load removal.

Telltale A strain indicator, usually comprised of a sleeved free-standing rod cast in place in a drilled pier or pile to measure relative movement between the anchored (embedded) tips of two or more rods or between the rod anchor and the top of the pier or pile.



Template A fixed template is required during all excavation and concreting operations when drilling from a barge. This is to maintain shaft position and alignment. A template is not required on land if the contractor can satisfactorily show that he can maintain proper position and alignment without it.

Temporary Casing Casing left in place until concrete has been placed, or casing placed as protection for workmen or inspector.

Test Hole With the test hole, the contractor must demonstrate that his construction methods will work. A test hole is typically the same size as the shafts to be constructed.



Tremie (1) (verb)To place concrete below water level though a pile, the lower end of which is kept immersed in fresh concrete so that the rising concrete from the bottom displaces the water without washing out the cement content. (2) (noun) The hopper and drop pipe used to place the concrete underwater.

Tremie Pipe The tremie pipe is used to place concrete in the drilled shaft. In shafts constructed by the wet method, the tremie pipe must extend to the bottom of the drilled shaft. In shafts constructed by the dry method, the tremie pipe must extend to within five feet of the shaft bottom. The tremie pipe serves several purposes. It transports the concrete through the slurry. It keeps the concrete from segregating during placement. Also, it



helps keep the concrete from mixing with the drilling slurry at the slurry/concrete interface.

Twisting Bar A tool attached to the kelly, used for "screwing" down casing through caving or squeezing soil. Sometimes used for pulling casing.

Underream Enlargement of the lower end of an augered or drilled pier hole to increase its bearing area. Also called "bell".

Underreamer, Belling Tool See Belling Bucket.

Unit Weight The weight per unit volume of a material such as soil, water, concrete, and so on. Typically expressed as pounds per cubic foot, rams per cubic centimeter, or kilograms per cubic meter.



Uplift An upward force exerted on a pier, pile, or other structural elements, by expanding soil or rock, hydraulic pressure, or structural loading.

Vibratory Driver/Extractor A pile-driving and extracting machine which is mechanically connected to a pile or casing and loosens it while driving or pulling by oscillating it through the soil. Power source may be either electric or hydraulic.

Vug A small cavity in a vein or in rock.

"Walking Off" Tendency for a rotating bit to deflect laterally when encountering harder, deflecting layer of rock or irregular surface.



Water Content The ratio of the quantity (by weight) of water in a given volume of soil mass to the weight of the soil solids, typically expressed as a percentage.

Water Table The subsurface elevation at which free water will usually be present. Also called "groundwater".












Drilled Shaft Tutorial - Appendix B


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Appendix B

Inspector Math tip sheets

VOLUME OF A SHAFT

EQUATION EXAMPLE

VOLUME OF A BELL

EQUATION EXAMPLE

VOLUME OF A TOE OF BELL

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EQUATION EXAMPLE

CIRCUMFERENCES

SI Conversion Factors

APPROXIMATE CONVERSIONS FROM SI UNIT

Symbol When You Know Multiply By To Find Symbol

LENGTH

mm millimeters 0.039 inches in

m meters 3.28 feet ft

m meters 1.09 yards yd

km kilometers 0.621 miles mi

AREA

mm^2 square millimeters 0.0016 square inches in^2

m^2 square meters 10.764 square feet ft^2

ha hectares 2.47 acres ac


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km^2 square kilometers 0.386 square miles mi^2

VOLUME

ml milliliters 0.034 fluid ounces fl oz

l liters 0.264 gallons gal

m^3 cubic meters 35.71 cubic feet ft^3

m^3 cubic meters 1.307 cubic yards yd^3

MASS

g grams 0.035 ounces oz

kg kilograms 2.205 pounds lb

TEMPERATURE

°C Celsius 1.8 C + 32 Fahrenheit °F

WEIGHT DENSITY

g/cc grams per cubic centimeter 62.4 poundforce/cubic foot pcf

kN/m^3 kilonewton/cubic meter 6.36 poundforce/cubic foot pcf

FORCE and LOAD

N newtons 0.225 poundforce lb

kN kilonewtons 225 poundforce lb

kg kilogram (force) 2.205 poundforce lb

MN meganewtons 112.4 tons (force) t

PRESSURE and STRESS*

kPa* kilopascals 0.145 poundforce/square inch psi

kPa kilopascals 20.9 poundforce/square inch psi

MPa megapascals 10.44 tons per square foot tsf

kg/cm^2 kilograms per square cm 1.024 tons per square foot tsf

Notes: 1 kPa = kN/m2 = one kilopascal = one kilonewton per square meter For dimensionless graphics and equations, a reference stress of one atmosphere can be used, such that σa = ρatm = 1 bar = 100

kPa = 1tsf = 1 kpg/cm2

Shaft Areas and Volumes

Per Linear Foot

Shaft Diameter (in) Volume (yd^3) Side Shear Area (ft^2) Bearing Area (ft^2)

12 0.03 3.14 0.79

14 0.04 3.67 1.07

16 0.05 4.19 1.40

18 0.07 4.71 1.77

20 0.08 5.24 2.18



22 0.10 5.76 2.64

24 0.12 6.28 3.14

26 0.14 6.81 3.69

28 0.16 7.33 4.28

30 0.18 7.85 4.91

32 0.21 8.38 5.59

34 0.23 8.90 6.31

36 0.26 9.42 7.07

38 0.29 9.95 7.88

40 0.32 10.47 8.773

42 0.36 11.00 9.62

44 0.39 11.52 10.65

46 0.43 12.04 11.54

48 0.47 12.57 12.57

50 0.51 13.09 13.64

52 0.55 13.61 14.75

54 0.59 14.14 15.90

56 0.63 14.66 17.10

58 0.68 15.18 18.35

60 0.73 15.71 19.63

62 0.78 16.23 20.97

64 0.83 16.76 22.34

66 0.88 17.28 23.76

68 0.93 17.80 25.22

70 0.99 18.33 26.73

72 1.05 18.85 28.27

74 1.11 19.37 29.87

76 1.17 19.90 31.50

78 1.23 20.42 33.18

84 1.43 21.99 38.48

90 1.64 23.56 44.18

96 1.86 25.13 50.27

102 2.10 26.70 56.75

108 2.36 28.27 63.62

114 2.63 29.85 70.88

120 2.91 31.42 78.54

126 3.21 32.99 86.59



132 3.52 34.56 95.03 Shaft Areas and Volumes

Per Linear Meter

Shaft Diameter (cm) Volume (m^3) Side Shear Area (m^2) Bearing Area (m^2)

30 0.07 0.94 0.07

35 0.10 1.10 0.10

40 0.13 1.26 0.13

45 0.16 1.41 0.16

50 0.20 1.57 0.20

55 0.24 1.73 0.24

60 0.28 1.88 0.28

65 0.33 2.04 0.33

70 0.38 2.20 0.38

75 0.44 2.36 0.44

80 0.50 2.51 0.50

85 0.57 2.67 0.57

90 0.64 2.83 0.64

95 0.71 2.98 0.71

100 0.79 3.14 0.79

105 0.87 3.30 0.87

110 0.95 3.46 0.95

115 1.04 3.61 1.04

120 1.13 3.77 1.13

125 1.23 3.93 1.23

130 1.33 4.08 1.33

135 1.43 4.24 1.43

140 1.54 4.40 1.54

145 1.65 4.56 1.65

150 1.77 4.71 1.77

155 1.89 4.87 1.89

160 2.01 5.03 2.01

165 2.14 5.18 2.14

170 2.27 5.34 2.27

175 2.41 5.50 2.41

180 2.54 5.65 2.54

185 2.69 5.81 2.69

190 2.84 5.97 2.84



195 2.99 6.13 2.99

210 3.46 6.60 3.46

225 3.98 7.07 3.98

240 4.52 7.54 4.52

255 5.11 8.01 5.11

270 5.73 8.48 5.73

285 6.38 8.95 6.38

300 7.07 9.42 7.07

315 7.79 9.90 7.79

330 8.55 10.37 8.55

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