2.Construction of sub structure

By- Khan Nikhat naaz

1. Job Layout

1.Site Clearance1.Site Clearance is an important factor to be considered in the job layout plans , before commencement of project work 2.There should not be any obstruction like trees , plants , shrubs, bigger size stones, etc.

3. Approach road should be wide so as to allow the truck for loading and unloading the constructional material . If site ground is uneven , then it should be made plane , for this contouring is done in advance.4.In short site should be cleared by all the way, otherwise no activity can be launched in construction processes.

1. A plan in which the arrangements for placing site office, store room , labour quarter, medical aid center , godowns for keeping construction materials and other facilities are properly prepared is called as Job layout or site layout .

2.The arrangements for processes should be such that the work is done smoothly and in orderly manner.

2. Preparing Job Layout

3. Job layout depends upon three factors as follows:- a) Location , area and topography of the site .b) Method of construction.c) Nature and type of work.4. There should be proper co-relation and co-ordination among the different units.

3.Layout for load bearing and framed structure by Center line method

4.Layout for load bearing and framed structure by Face-Line Method

Correct measurement of distances , preferably by steel tape.

Use of level , either dumpy level or mason’s level.

Correct marking of face -line or center – line.

Use of correct plumb –bob for transferring points on ground

Checking of distances from at least two independent measurements .

5. Precautions while Marking Layout on Ground

6. Excavation for Foundation • Excavation of foundation ,trenches can be done

either manually with the help of conventional implements or with the help of special mechanical equipment.

• Excavate foundation along the line created by batter boards.

• Excavate remainder of soil inside the perimeter. • Don’t excavate inside soil if slab is on the grade.• If foundation is deep , taper edges are used to

prevent the collapse.• If soil is unstable or very deep , Use shoring method.

Timbering and strutting is a method of giving the temporary supports to the sides of trench , when the depth of trench is large or when the sub-soil is loose.

Timbering is also called as Shoring . It consists of timber boards and struts to give temporary support to the side of the trench.

7.Timbering and Strutting

Following are the methods of timbering and strutting :-

1. Box sheeting2. Stay bracing 3. Runner system 4. Vertical sheeting5. Sheet piling

If depth of the excavation is upto 4m and soil is loose , the box sheeting method is used.

It is just like box consisting of vertical sheets held in position by horizontal row of wales and made tighten by providing strut.

If soil is very loose, that time horizontal sheets are provided and supported by vertical wales and made tighten on both sides by horizontal strutting

Braces are provided when the height is more.

1. Box Sheeting

When the depth of excavation is upto 2m , then stay bracing method is adopted to support the sides excavated in fairly firm soil.

It consists of a vertical sheets or polling boards opposite to each other against the two walls of the trench and held these vertical sheets in position by strutting

2. Stay Bracing

This is used in extremely loose and soft ground which need immediate support as excavation process.

This system is similar to vertical sheeting of box system, except in place of vertical sheeting, runner, made of long thick wooden sheet or plank s with iron shoe at the end are provided.

Wales and Struts are provided as usual. These runner are driven about 30 cm in

advance of progress of the work, by hammering.

3. Runner system

1.It is similar to the box system , only difference is that in this case excavation is progressed in stages by providing an offset at the end of each stage. 2. This method is best suited for deep trenches in soft ground.

4. Vertical Sheeting

This method is adopted as follows :- When soil to be excavated is soft or loose. The Depth of excavation is large. When the Width of the trench is large. When there is sub soil water . Sheet piles

are used to resist the lateral earth pressure.

These are driven in ground by mechanical means .

They can also be used for excavating for very large depth.

5. Sheet Piling

Vertical sheeting and vertical Runner System

If the plinth depth do not exceed 450mm above the ground level and if the exposed ground is back cotton soil , then remove the black cotton soil so as to avoid the uneven settlement of ground flooring.

In process of plinth filling watering and compaction should be carried out till the required level is reached so as to from a thoroughly compacted base.

The material for plinth filling consist of hard murum and broken rubbles.

On the compacted surface or consolidated plinth filling , a concrete bed of thickness of 80 mm is done for laying the tile work further.

Material for Plinth Filling

Lead and lift are the terms related to excavation of earth / soil.

LEAD : 1.The horizontal distance up to which a contractor will haul the material excavated and it is included in the rates of excavation is called as Lead. 2.The lead is 30m and called as Standard or normal lead.

Lift : 1. The vertical distance up to which a contractor will haul the material excavated and it is included in the rates of excavation is called as Lift. 2. The lift is 1.5m and called as Normal lift.

Lead & Lift in Excavation

SUB-STRUCTURE OR FOUNDATION is the lower most portion of the building, usually located below the ground level, which transmits the load of super structure to the supporting soil. A foundation is therefore that part of the structure which is in direct contact with the ground to which the load are transmitted.

Foundation

Purpose of foundation To distribute the total load coming on the

structure on a larger area. To Reduce the load Intensity To support the structures. To give enough stability to the structures

against various disturbing forces, such as wind and rain.

To prepare a level surface for concreting and masonry work.

For the Lateral Stability.

1. Open Foundation. 2. Shallow Foundation :- Types of shallow foundation :- 1] Stepped Foundation a)Wall footing , b) Reinforced concrete

footing c)Column footing :- 1.Isolated , 2. Combined ,3.Raft foundation.

3.Deep foundation :-1. Pile foundation ,2.Well foundation, 3.Coffer dams.

Types of foundation

This is simply a layer of foundation concrete provided at the base of a column, pedestal or wall.

This type of foundation is provided when hard stratum is available at very shallow depth or the work is unimportant e.g. Compound wall , pillars for barbed wire fencing etc.

1.Open Foundation

When the foundation is placed immediately below the lowermost part of structure it is called as SHALLOW foundation.

It can also be defined as, when the depth of foundation is less than or less than equal to the width;, the foundation is called as SHALLOW FOUNDATION.

PURPOSE: The purpose of shallow foundation is to distribute the structural load over considerable horizontal area .

LIMITATION:-1. The load carrying is considerably less as compared

with deep foundation.2. Can not be used under marshy land, made up of

ground water or water logged area.

2.Shallow Foundation

Stepped foundations = In this case , the base of the foundation is made wider to distribute the load on wider area .

A) Wall footing : 1.It can be achieved by constructing several courses of bricks widening the base, the lowest course is usually twice the breadth of the wall. 2. The sectional elevation of brick wall footing and stone wall footing is shown.

Stepped Foundations

B)Reinforced Concrete Footing :- When the bearing capacity of the soil on which the wall footing is to rest is very low and when the walls are subjected to heavy

loading , under such circumstances the reinforced concrete footing is used

C) Column footing :- 1.Isolated : It is provided under a column or other similar member for the distribution of concentrated load in the form of uniformly distributed load on the soil below.The shape may be square, rectangular or circular in plan . It may be constructed either in brick masonry , stone masonry or R.C.C. steel grillage etc.

2. Combined : Combined column footing is provided as a common footing for two or more columns.

This type of column helps in reducing the depth of foundation and unequal settlement can be avoided.

In this type of footing ,a common P.C.C bed is provided on which two or more column rest.

Combined footing is also provided when column are very near to each other and isolated column will over lap each other.

Shear force calculation is important in combined footing

Combined footing

C) Raft Foundation :-When bearing capacity of the

supporting soil is very low and heavy concentrated structural loads are to be supported in case of marshy land or made of soft clay.

It proves to be economical under water logged area.

Raft is acting as a floor consisting of thick reinforcement concrete slab covering the entire area of the bottom of the structure.

Raft Foundation

When the depth of foundation is more than its width the foundation is called as DEEP foundation.

It can also be defined as , if the depth of foundation is more than 2.00 m, it called as deep foundation.

3.Deep foundation

1) Piles A).Depending upon the function :- 1. Bearing piles 2.Friction piles 3.Sheet piles 4.Anchor piles 5.Batter piles 6.Fender piles 7.Compaction piles

Types of Deep foundation

1. BEARING PILES: These are driven into the ground until a hard stratum, directly supported on

hard base and pile act as pillar to transmit the load.

2. Friction pile : When the soil is soft to a considerable depth the pile which is required to be driven is called FRICTION PILE.

The load carried by a pile is borne by the friction developed between the side of the pile and the surrounding is called as SKIN FRICTION.

3.Sheet Pile :They are used to retain soil which is liable to escape laterally when subjected to pressure or to enclose the area for some foundation and to protect the area from the flowing water.

ANCHOR PILE: when piles are used to provide anchorage against horizontal pull they are called as ANCHOR PILE.

BATTER PILES: When the piles are driven at an inclination to resist large horizontal or inclined forces then the piles are called ac BATTER PILES.

FENDER PILES: when the water front structure or concrete check is required to protect from impact or abrasion caused by the ship then the fender pile is used at the front.

COMPACTION PILE: when the piles are driven to increase the bearing capacity of the granular soil they are called as compaction pile

B) Depending upon the material :-

1.Timber piles 2.Concrete piles 3.steel piles

Economical for supporting light structures Timber from sal, deodar , babul , khair, is

used . the pile cap of iron ring of about 25 mm is

provided to prevent the pile head from brooming .

The lower end of the pile is provided with a cast iron conical shoe.

The load transfer mechanism is by skin friction hence there should a minimum distance of about 60 cm center to center

1.Timber pile

ADVANTAGES:1. Economical.2. Can be driven rapidly hence saves time.3. Due to its elasticity it is recommended in

region where the piles are likely to be subjected to lateral forces

4. Heavy machinery and skill supervision is not required.

DISADVANTAGES:1. Should be cut of above ground water table

to prevent decaying.2. Timber cannot be driven in filled up ground.3. Likely to decay by salt water or insect.4. Restricted length .

Concrete piles are classified as :- 1. Pre-cast piles. 2.Cast in – situ pile. 3. Pre-stressed concrete pile

2. Concrete Pile

1.PRE-CAST CONCRETE PILE: Precast piles are those which are manufactured

in the factory or at a place away from the construction site and then driven to the ground at the place required.

Pre cast pile may be square ,octagonal, or round in cross section or may be tapering or parallel in longitudinally. The size of these piles varies from 30cm to 50cm in cross sectional dimension and up to 30m in length .

Precast pile are useful in carrying fairly heavy loads through soft material to firm strata .

2. Cast in – Situ pile :- The piles which are cast in position on site inside the ground , it may be reinforced when pile act as column and when subjected to lateral force.

Normally the cast in situ piles are constructed with an enlarged bulb and corrugated stem.

A steel tube having internal diameter equal to the diameter of the pile and 20mm thickness is driven into the ground

when the has been driven up to the desired depth a charge of concrete is poured and the tube is gradually withdrawn and thus alternate pouring and withdrawing of tube , the pile is constructed to the full length.

In case the pile is to be reinforced , the reinforcement cage is lowered in the steel tube before pouring the concrete.

3. Pre – Stressed concrete piles :Pre stressed piles are stronger than the normal reinforced pile . Therefore , because of the reduction in cross sectional, they are lighter and more easily handled.

It has greater ability to withstand extremely hard driving.

It more durable in sea water because of the crack.

It has great column It has lesser handling cost because of light

weight. It has much lager moment of inertia then the

conventional pile of the same dimension .

Advantages of concrete piles :-

These piles cannot be driven rapidly. It requires skilled technical supervision heavy

driving machinery. To withstand handling stresses, reinforcement is

essential.

Disadvantages of Concrete piles

A steel pile may be a rolled section , a fabricated shape or a piece of sheet piles

Metal piles have been used in from of cast iron pipes or solid wrought iron shaft .

These piles are excepted to penetrate through hard rock.

Types of steel pile. H-PILES, PIPIE-PILE, SCREW PILE, DISC PILE. The pipes is normally filled with concrete and

the diameter varies from 25cm to 125 cm and the depth is 30m or more.

3.Steel Pile

Caisson The caisson is a structure used for the purpose of

placing foundation in correct position under water. It is Permanent in nature. Used to pump out water in under water concreting

work. Types of caisson:1. Box caisson2. Open caisson3. Pneumatic caisson

2. Well foundation Caisson is a foundation which comes under the type of well

foundation.

Open caisson is a box of timber, metal, reinforced concrete or masonry

Open at both end (top and bottom) Whenever consideration for scour or bearing

capacity required foundation being taken to depth of more than 5 to 7m

Costly and uneconomical (heavy timbering required)

Due to greater earthwork, the progress of work is very slow

1. Open Caisson :-

A box caisson open at top and close at bottom.

It is Made up of timber, concrete or steel.

Built on land and floated to pier site where it is sunk in position

Used where bearing stratum is available and loads are not heavy

2.Box Caisson :-

DEFINITION: It is a temporary structure constructed in a river or lake or any other water bearing surface for excluding water from a given site to enable the water building operation to be performed under dry conditions. walls are water tight

Temporary structure Built within or in pairs across a body of water Allows the enclosed space to be pumped

out ,creating a dry work environment.

3.Cofferdams

1. Earth filled cofferdams .2. Rock filled cofferdams .3. Sheet pile cofferdams :-a) Single wall cofferdams,b) Double wall cofferdams.

Types of cofferdams

Earthen cofferdam consist of earthen embankment built around the area to be enclosed.

It can be constructed if the water depth is more than 1.4 to1.8m and the velocity of the flowing water is very low.

Top width of the dam should not be less than 1.00m and the side slope may vary from 1:1.5 to 1:1.2. the inner portion called as embankment consist of clay and sand or clay or gravel

1. Earth filled Cofferdams

Earth filled cofferdams

In case of a rock filled cofferdam , the depth of water to be retained is of order of 1.8 to 3.00m .stone or rubble is used for embankment

2.Rock Filled cofferdams

2.Rock Filled cofferdams

1.Single wall cofferdams If the area to be enclosed is very small and the depth

of water is about 4.5 to 6.0m then timber piles known as guide piles are first driven deep into the firm ground below the river bed, the distance between the piles may vary from 1.7 to 3.5m depending upon the velocity of the flow.

Then Wales are bolted to guide piles at suitable distance

Then sheet or wooden sheet piles are driven into the river bed along the Wales and secured by bolts to the Wales.

Thus , the area can be enclosed and the water is pumped out to start the construction in dry condition.

3. Sheet pile cofferdam

2. Double walled cofferdam If the area to be enclosed is very large

and if the depth of water is large then double wall cofferdam are used instead of single wall cofferdam.

The construction is same , only in case of a single wall a pair of wall with a gap between is provided.

This is suitable up to a depth of 10 to 12.0m

To prevent leakage the sheet piles are firmly driven into the ground.

Sheet pile cofferdam

For Water Logged Foundation It Is Essential To Carry Out Dewatering Of Soil Before Carrying Construction Activity. Methods Of Dewatering1. Sumps and Ditches2. Well Point System3. Deep well System4. Vaccum Method

Dewatering of foundation by Pumping Method

This is the simplest form of dewatering used in shallow excavation in coarse grained soils.

Sallow low pits ,calls as sumps are dug along the periphery of the area drainage ditches.

The water from the slope or sides flows under gravity and is collected in sumps from which it is pumped out.

1. Sumps and Ditches

Sumps and Ditches

A well point system is a perforated pipe of 5 to 8 cm in diameter and one metre long covered by cylindrical wire gauge screen known as STRAINER.

These pipes are joined to a horizontal pipes known as HEADER pipe.

2. Well point Systems

Well point Systems

3. Deep well system :-This system is suited when the depth of excavation is more than 16m.

In this method a hole of 30cm diameter is bored around the well point and the riser pipe.

It then sealed using bentonite ,soil-cement or clay. The header pipe is then connected to vacuum pump for removal of water.

4. Vacuum Method

These foundations are provided when the bearing capacity of the soil is low and hard strata is not available on the given site.

The most commonly constructed special foundation are 1. Mat or raft foundations , 2.Under-reamed piles .

Special Foundation

When bearing capacity of the supporting soil is very low and heavy concentrated structural loads are to be supported in case of marshy land or made of soft clay.

It proves to be economical under water logged area.

Raft is acting as a floor consisting of thick reinforcement concrete slab covering the entire area of the bottom of the structure

1. Mat or Raft Foundations

Mat or Raft Foundations

The under reamed piles are the best solution for foundation black cotton soil.

Bored cast in situ concrete piles having bulb shaped enlarge base

Such structure is anchored to the ground at depth where ground movement due to change in moisture content negligible

Bearing capacity increased by increasing the number of bulbs Hand auger or machine auger used for boring with extension

rod After boring upto certain depth the base of hole is enlarged in

the form of bulb

2. Under- Reamed Piles

Under- Reamed Piles

Bearing capacity of soil is the is the intensity of the load per unit area of the foundation . If the bearing capacity is not sufficient , then the use of special type of foundation becomes imperative.

Bearing capacity of the sub soil or foundation soil is measured by plate load type.

In this method, the bearing plate is square of minimum size 30cm square, and maximum size 75 sq.cm .

The thickness of the plate should not be less 25mm.

BEARING CAPACITY OF THE FOUNDATION.

1. Break direct contact between soil and masonry.2. Construction should be taken in dry season.3. Masonry should be start at least 15 cm below the ground

level.4. Mostly raft foundation should be provided.5. Under reamed pile foundation is ideal foundation.6. To take the foundation at such depths where cracks cease

to extend.7.To provide reinforced concrete ties or band all around the

main wall of the building.8.Under –reamed piles are ideal for foundation in black cotton

soil.

Precaution to be taken while constructing the foundation black cotton soil:

ThThank you………