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Hydraulic Piling Hammers
1. Drop hammer:
The
drop hammer in the pile driving equipment consists of a heavy ram in between the leads. The ram is lifted up to a certain height and released to drop on the pile. This type is slow and therefore not in common use. It is used in the cases where only a small number of piles are driven.
2. Single acting hammer:
In a single acting hammer a heavy ram is lifted up by steam or compressed air but dropped by its own weight. The energy of a single acting hammer is equal to the weight of the ram times the height of fall.
3. Double-acting hammer:
The double-acting hammer employs steam or air for lifting the ram and for accelerating the downward stroke. The energy of a double-acting hammer is equal to the (weight of the ram I mean effective pressure I the effective area of ram) 1 times the height of fall.
4. Diesel hammer:
The diesel hammer is a small, light weight and highly mobile. They use gasoline for fuel. To start the operation, the ram is raised, and the fuel is injected. As the ram is released, the ram falls and compresses air and fuel. The air and fuel becomes hot because of the compression and the air-fuel mixture is ignited. The resulting explosion
1. Advances the pile and
2. Lifts the ram. If the pile advance is very great as in soft soils, the ram is not lifted by the explosion sufficiently to ignite the air-fuel mixture on the next cycic, requiring that the ram be again manually lifted.
5. Vibratory hammer:
The principle of the vibratory driver is two counter-rotating eccentric weights. The driving unit vibrates at high frequency and provides two vertical impulses, one up and one down. The downward pulse acts with the pile weight to increase the apparent gravity force. These hummers have reduced driving vibrations, reduced noise, and great speed of penetration.
Hammer Selection:
Generally the size of hammer is more important factor than type of hammer. A heavy pile should be driven by a heavy hammer delivering large energy. Preferably the weight of HKjmcr should beat ^H HB1 the total weight of the pile and the deriving energy should be at Hpiie foot-pound for each pound of pile weight. Each type of hammer has its use under suitable conditions, The advantages and disadvantages of cach type are summarized below:
Single-acting hammer :
They arc advantageous when driving heavy piles in compact or hard soils; the heavy ram striking at - tow velocity produces least damage due to impact. The disadvantages arc low driving speed and large headroom requirement.
Double-acting hammer:
They are generally used to drive piles of light or moderate weight in soils of average resistance against driving. This type of hammer can drive piles at fast speed, requires less headroom and can be used to extract piles by turning them [i.e. the double-acting hammer] upside down.
Diesel hammer:
They are similar in application as double-acting hammers, but driving may become difficult in extremely soft ground.
Vibratory hammer:
They have fairly good results in silty and clayey deposits. They are used in heavy clays or soils with appreciable numbers of boulders. See above for other advantages.
Hammer Type Efficiency (ɳh)
Single and double acting hammer 0.7 - 0.85
Diesel hammers 0.8 - 0.9
Drop hammers 0.7 - 0.9
Common Pile Driving Problems and SolutionsPile Driver Problems
By Juan Rodriguez, About.com GuideSee More About:
soil
footings
Common Pile Driving Problems and Possible Solutions to be Implemented.
1. Piles With Blow Count Above Minimum Pile Penetration Requirements.
Courtesy of Fernandez Tadeo.
Check the pile has sufficient drivability and that the driving system is matched to the pile.
If the pile and driving system are suitably matched, check driving system operation for
compliance with manufacturer’s guidelines. If no obvious problems are found, dynamic
measurements should be made to determine if the problem is driving system or soil
behavior related. Driving system problems could include preignition, preadmission, low
hammer efficiency, or soft cushion. Soil problems could include greater soil strength than
anticipated, temporarily increased soil resistance with later relaxation (required restrike to
check), large soil quakes, or high soil damping.AdsJINYA-steel buildings www.jinyaprefab.com Professional steel buildings high efficiency,energy saving!Hydraulic Hammers www.aone1.co.kr Hydraulic Hammers / Breakers Construction Spare parts A to ZHydraulic Rock Breaker www.equipbank.com Excellent Quality Very Good Price made in Korea
2. Piles Driving Significantly Deeper Than Estimated.
Soil resistance at the time of driving could be lower than anticipated or driving system
performance is better than anticipated. Perform restrike tests after an appropriate waiting
period to evaluate soil strength changes. If the ultimate capacity based on restrike blow
count is still low, check drive system performance and restrike capacity with dynamic
measurements. If drive system performance is as assumed and restrike capacity low, the
soil conditions are weaker than anticipated. Foundation piles will probably need to be
driven deeper than originally estimated or additional piles will be required to support the
load. Contact the structural engineer/designer for recommended change.
3. Abrupt Change or Decrease in Blow Counts for Bearing Piles.
Courtesy of Fernandez Tadeo.
If borings do not indicate weathered profile above bedrock/bearing layer, then pile toe
damage is likely. For piles that allow internal inspection, reflect light to the pile toe and
tape the length inside the pile for indications of toe damage. For piles that cannot be
internally inspected, dynamic measurements could be made to evaluate problem or pile
extraction could be considered.
4. Blow Count Significantly Lower than Expected.
Review soil borings. If soil borings do not indicate soft layers, pile may be damaged below
grade. If the pile was spliced, re-evaluate splice detail and field procedures for possible
splice failure.
5. Lateral Movement of Previously Installed Piles When Driving New Piles.
Pile movements likely due to soil displacement from adjacent pile driving. Possible
solutions include redriving of installed piles, change in sequence of pile installation, or
predrilling of pile locations to reduce ground movements. Lateral pile movements could
also result from adjacent slope failure.
6. Piles Driving Out of Alignment.
Courtesy Fernandez Tadeo
Piles may be moving out of alignment tolerance due to hammer-pile alignment control or
due to soil conditions. If due to poor hammer-pile alignment control, a pile gate, template
or fixed lead system may improve the ability to maintain alignment tolerance. Soil
conditions such as near surface obstructions or steeply sloping bedrock having minimal
overburden material may prevent tolerance from being met.
7. Piles Driving Out of Location.
Piles may be moving out of location tolerance due to hammer-pile alignment control or due
to soil conditions. If due to poor hammer-pile alignment control, a pile gate, template or
fixed lead system may improve the ability to maintain location tolerance.
For piles encountering shallow obstructions:
If obstructions are within 3 feet of working grade, obstruction excavation and removal is
probably feasible. If obstructions are at deeper depth, are below the water table, or the soil
is contaminated, excavation may not be feasible. Spudding or predrilling of pile locations
may provide a solution.
8. Pile Obstructions at Depth.
If deep obstructions are encountered contact the engineer for remedial design. Ultimate
capacity of piles hitting obstructions should be reduced based upon pile damage potential
and soil matrix support characteristics. Additional piles may be necessary.Adshydraulic breaker hammer www.gbhammer.com South Korean Manufacturer GB manufactures wide range-breakerPVE Piling & Drilling Rig www.pvepiling.com specialized piling & drilling rigs & hydraulic impact hammers
9. Concrete Piles Develop Partial Horizontal Cracks in Easy Driving.
Check hammer-pile alignment since bending may be causing the problem. If the alignment
appears to be normal, tension and bending combined may be too high. The possible
solution is as above with complete cracks.
10. Concrete Pile Spalling or Slabbing Near Head.
Courtesy Fernandez Tadeo
Determine pile head stress for observed blow count and compare with allowable stresses. If
high calculated stress, add pile cushioning. If low calculated stress, investigate pile quality,
hammer performance, hammer-pile alignment
Precast Pile
Foundation: Foundation is the lowest part of a structure which provides a base for the super-structure and transmits the loads (live load, wing load) on the structure including the dead weight of the structure itself to the soil below. Types of Foundation: Foundation can be broadly classified into two types–
Deep Foundations Shallow Foundations
The most common forms of construction pertaining to deep foundation are: Piles Cofferdams Caissons.
The various types of shallow foundation are: Spread footing Grillage footing Eccentrically loaded footing Combined footing Mat or Raft foundation.
Importance of Pile foundation: Enables a structure to be supported by a layer of soil Provide safe foundation Used for - Buildings Trestles
Bridges
Classification of Piles: Depending upon materials used in their manufacture,Piles can be classified as:
a) Concrete Pileso Cast-In-Place or cast-in-situ Pileso Pre-cast Pileso Pre-stressed concrete Piles
b) Steel Pilesc) Timber Pilesd) Composite Piles
Classification of pile based on function Bearing pile Friction pile Sheet pile Anchor pile Batter pile Fender pile Compaction pile
Precast Pile Pre means before & cast means made. So precast pile refers to a pile which is made before, it is being used.
Most common pile
Francois Hennebique first use it (1897)
A.A.Raymond built his company(1901)
It can be constructed either in the factory or on site
It is reinforced concrete pile
PRECAST PILES SHAPE& SIZE
Commonly manufactured in square ranging from about250 mm to about 450 mm
maximum section length of up to about 12 m
1. Hexagonal
2. Circular
3. Octagonal
4. Triangular
5. H shapes
Soil suitability Suitable in a wide range of soil condition
working loads in excess of 1000kN Useful for very deep piling up to 40 m in soft ground or in aggressive or contaminated soils
Bearing capacity• High bearing capacity• Compact soil & increase the bearing capacity• Concrete formations around the contracted sections increase the capacity.
Design of Precast Pile By the soil test, we would be find the depth of penetrate. By which length of a pile can be determined. After determine the total weight of the building, we would find the number of piles. The diameter of the pile normally varies from 35 cm to 65 cm and their length varies from 20 ft to 30
ft. Besides bearing load for easy transportation & movement big weir or reinforcement is used in the pre
cast pile.
For easy driven rectangular pile is often made. Longitudinal reinforcement usually consists of one bar 20 mm to 50mm in diameter at each angle of
the section of the pile. The vertical rods are tied horizontally by bars 6mm to 10mm in diameter. The horizontal bars may be provided in the form of stirrups wound around the verticals. Pile shoe & pile stirrup is used in the lower part of the pile to driven the pile easily.
Process of precast pile Steel form is used for the precast pile manufacture. Before pore the concrete in to the form, Mobil or other kinds of oil have been used. Cement, sand, aggregate ratio is normally 1:2:4 in pre cast pile.
But to make the foundation stronger mix ratio should be 1:1.5:3. When the concrete pore in the steel form it would be ramming by the vibrator. After 3 days, piles have been covering by the sheet. After 3 days of casting, steel form would be removed. Then the piles would be prepared for 4 weeks curing. Then the piles are transported to the site for driving.
Pile DrivingIt is the process of driving piles into the ground.It requires few piling equipment such as- Cranes
Hammers
Cushions
Leads
Piles
Templates
Piles are driven in the ground by the following methods:1. By drop hammer
2. By steam hammer
3. By water jets
4. By boring.
By Drop Hammer:It is a pile driver in which the hammer is raised by a rope or cable then allows the drop on the pile cap.
Pile Installation Using Drop HammerNormally, 1.5 to 3 meter from above, the drop hammer would be put down in to the pile cap.The weight of drop hammer varies from 230 to 1800 kg.
By using the pile wipes machine, the drop hammer would be controlled.
The exact weight of the drop hammer to be used is governed by the shape and length of pile as well as nature of ground to be penetrated.
By Steam HammerIn this type of pile driver the hammer is automatically raised and then dropped a short distance by means of a steam cylinder and piston. There are two types of steam hammer pile drivers:
Single acting type. Double acting type.
The hammers usually weight 2000 to 4000 kg and have a stroke length up to 15m. In case of single-acting steam hammer or drop-hammer the stroke length of fall should not exceed 1.35m.
By Water Jets
This method of driving piles involves displacing the soil below the shoe of the pile by means of one or more jets.
The jet consists of a 5 to 6cm diameter pipe with its lower end decreasing in diameter and forming a nozzle of about half the diameter of the pipe at top.
Water is forced through the pipe under a pressure of 7 to 17.5 kg/ sq.cm.
The nozzle of the jet of the jet pipe is usually kept about 15 to 30 cm below the pile shoe.
The water jet is stopped a few meters before the pile reaches its required depth and it is driven by hammering for that distance.
By BoringIf the pile is required to penetrate beds of hard soil, or soft rock to reach its required depth, driving of the pile by boring is an economical solution. In dry soils, boring may be done by auger, while in soft rocks, rotary well drills may be used.
The bore is made to the required depth of the pile. Precast piles are then put in the bore hole.
Advantages of pre-cast piles:
They can be cast well before the commencement of the work resulting in rapid excavation of work.
Their construction can be well supervised and any defect detected can be rectified before use.
The reinforcement remains in their proper position and do not get displaced.
They can be driven under water
The driving of adjacent pile does not produce adverse effect upon the already driven pile.
They can be loaded soon after they have been driven to the desired depth.
Disadvantages of pre-cast piles: They are heavy and great difficult is experienced for their handing and transportation.
The exact length of a pile can rarely be pre-determined and as such it has to be lengthened sometimes, rendering the pile weak at the joint.
If a pile is found to be too long after driving, it has got to be cut down which involves extra labor, time and expense.
They are subjected to the driving shocks after the concrete has fully set. This may result in unsound construction.
Precast pile cannot be long.
Precast pile creates shake that can harm other structure.
Precast pile cannot be done in busy areas and highly populated areas
The piles are difficult to manufacture
It is not economical
Subject to longitudinal and transverse cracking
Not aesthetic
Not appropriate for curved or flared structures
Complicated for skews
SolutionIf only quality of pile is considered then precast pile is much better than cast in situ pile. But due to the difficulties & expense in transport & hammering the use of precast pile is rare in Bangladesh. If the depth of deep foundation is 20 to 30 feet, then precast pile is much better than cast in situ pile with the consideration of all circumstances.
Difference of cast in situ & precast pile
Precast pile Reinforcement remains in their proper position. Can be loaded soon after they have been driven Can be driven under water Defect can be rectified before use They are costly Exact length of pile can rarely be predetermined
Cast in situ Possibility of the reinforcement getting displaced Can’t loaded soon after they have been driven Can’t be used under water Defect can’t be rectified They are not costly They are cast in exact length
Difference of theoretical & practical
Theoretical We can joint two pile together Maximum length 40 ft All of the test have to done before use
Practical We use one pile to drive They use 50~55 ft pile They only do some test in site
