construction technology i

8/8/2019 Construction Technology i

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CONSTRUCTION TECHNOLOGY

Avery structure consists of two parts

1) Sub Structure (foundation).

2) Super Structure (above ground level).

Foundation

The lowest artificially prepared part of the structure which are in direct contact with the

soil (or) ground and which transmit the load of the structure to the ground are known as

foundation.

The solid ground on which the foundation rest is called foundation bed (or) foundation

solid.

Objects (or) purpose of foundation

1. To distribute total load coming on the structure over a large area evenly and thus

prevent uneven settlement.

2. To provide a level surface for building operations.

3. To give enough stability to the structure against various disturbing forces.

4. To take a structure deep into the ground and thus increase its stability, preventing over

turning.

Types of foundation

Foundation can be broadly classified in to two types:

1) Shallow foundation.

2) Deep foundation.

Shallow foundation : According to Terzaghi a shallow foundation is one its depth is

equal to (or) less then its width.

Deep foundation : When the depth of the foundation is greater then its width, then

it is called deep foundation. Generally they are called pile

foundation.

I. SHALLOW FOUNDATION

Types of Shallow foundation

a) Spread footing.

b) Grillage foundation.

c) Combined footing.

d) Matt (or) Raft foundation.

e) Eccentrically loaded footing (or) foundation.

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a) Spread footing : When the foundation is placed immediately beneath the lowest part

of the super structure in such case a spread is provided under the

base of a wall (or) a column this spread is known as footing and the

foundation is known as spread foundation.

b) Grillage foundation :

When heavy structural load from column, piers are required to transmitted to a soil of low

bearing capacity, grillage foundation is often found to be lighter and more economical.

This avoid deep excavation. This type of foundation the depth is limited 1m to 1.5m and

the width is considerably increased to bring the pressure on the soil with in permissible

limit. The whole structure is rest on two perpendicular tier of RSJ (Rolled steel joist) asshown in the Fig.

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c) Matt or Raft Foundation :

The footing and bed concrete is provided over the full plinth area of the structure when the

bearing capacity of the soil is very poor. This is common footing for no. of columns.

4) Continuos (or) combined footing :

In this type of construction the footing for 2 (or) 3 adjacent column are made continuos byproviding beam between the successive footing. This type of footing is cheaper than raft

foundation and it is adopted to avoid differential (or) uneven settlement of the soil and to

make the structure safe from earthquake disturbence.

A spread footing which support to two or more column is

termed as combined footing. If the independent spread footing

of two columns are connected by a beam it is called

Strap Footing.

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The combined footing may be rectangular in shape if both the

columns carry equal loads (or) combined footing may be

trapezoidal in shape. If they carry unequal loads. When two

columns loads are unequal with outer column carry heavy load

& when there is space limitations behind the outer columns a

trapezoidal combined footing is provided.

STRAP (or) CONTILEVER FOOTING :-

A strap footing may be used where the distance between column

is more that has combined footing. Strap footing consist of

spread footing of two column connected by strap beam.

In case of eccentric loading (for the exterior column) a concrete

footing for interior column is connected by a strap.

While in a soft soil & under heavy loading conditions there is adanger of the maximum pressure at the out column exceeds the

bearing of capacity of soil the load from the outer column is

balanced by load from interior column thus a cantilever beam

(strap).

FOUNDATION OF BLACK COTTON SOIL

Construction on black cotton soil commonly known as shrinkable soil as always been a

difficult problem for engineers.

Black cotton soil is dangerous for buildings an account of its volumetric changes with the

change of atmospheric conditions. An account of alternative swelling and shrinkage

(change in volume) the differential settlement of the structure taken place.

Precautions for the safety of foundations in black cotton soil :

i) To limit the load on the soil to 5.5 ton / Smt. If water is liable access in the foundation

limiting should be restricted to 409 ton/ Smt.

ii) For important structure the matt foundation to be adopted.

iii) The black cotton soil should be completely removed if possible and economical.

iv) The depth of foundation should extend behind depth of cracks in black cotton soil.v) The black cotton soil should not be allowed to come in direct contact with the

foundation masonry.

vi) The construction work should be carried out in dry conditions.

vii)The foundation work and the black cotton soil are separated by a layer of sand

(or) some such loose materials.

viii)In case of ordinary building the foundation should be taken at least 30cm deeper than

the depth where the cracks stops.

ix) For less important structure the foundation preferably taken at least 15cms behind the

cracks.

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Method 1

When the depth of the soil is more and there is not changes

for water from the surface to penetrate thru the soil for more

then 1 mtrs to 1.5 mtrs in that cases the depth of the

foundation is excavated 30cms behind the depth of cracksand foundations bedding is placed over the gravel bedding

of 50 cms thick & sides of the foundation pit is filled by

sand.

Method - 2

In case of special type of structure in black cotton soil. The

footing is rest over R.C.C slab of thickness 12 cms to 15cmsover a concrete at the edges and in between and sides and is

filled to avoid direct contact of foundation to the black

cotton soil. At 1.5 cms c/c through out the length of the

foundation 80 mm dia pipe is inserted (or) embedded to

drain off excess humidity whenever required by allowing the

hot air through the pipe to dry off sub soil (or) foundation

soil.

CAUSES (OR) FAILURE OF FOUNDATION AND TO PREVENT SUCH CAUSES

The main causes (or) failure of foundation are

1. Un-equal settlement of sub soil.

2. Un-equal settlement of masonry.

3. Horizontal movement of the soil adjoining the structure.

4. Lateral pressure tending to over turning the structure.

5. Atmospheric action.

6. Transpiration of tress and shrubs.

7. Shrinkage due to withdrawal of moisture from the soil below the foundation.

Preventive Measures

1. Un-equal settlement of sub soil.

This occurs due to various reasons such as un-equal distribution of load on the foundation,

varying bearing power of sub soil, eccentricity of the load.

To prevent such failure :

a. Foundation should rest on hard soil.

b. Design of foundation should be appropriate to the nature of sub soil.

c. In any case the pressure on the soil should not exceed the SBC of soil.

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d. As far as possible foundation should be so proportionate that the centre of gravity of

load on structure coincide with center of gravity of the foundation.

2. Un-equal settlement of masonry.

Mortar joints may shrink and compress when loaded excessively before it has fully set,improper bonding of masonry, low quality of material used.

The above reasons may lead to un-equal settlement of the masonry.


a. The mortar should either be very lean nor very stiff.

b. The masonry work should be raised evenly.

c. The progress of construction should not be more than 1.5 mtrs height in a day.

d. The quality of material used should be proper.

e. Proper curing should be done to masonry work.

3. Horizontal movement of the soil adjoining the structure.

Very soft soil is liable to give way under the action of load, especially at places such as

sloping ground , river banks, etc.,


a. To construct retaining wall.

b. To drive sheet piles, to prevent the escape of soil.

4. Lateral pressure tending to over turning the structure.

The thrust of a pitched roof (or) sloped roof (or) arch action (or) wind action on the super

structure causes wall to over turn.


a. Provide a sufficient wide base.

b. To design the foundation for the worst condition.

5. Atmospheric action.

Due to sudden changes in atmospheric condition ie., due to temperature and humidity it

causes rapid changes in volume incase of black cotton soil and also in masonry to cause

due to development of the crack (or) settlement of foundation.

To prevent such causes the masonry work should properly protected by plastering, white

washing (or) provided by shadow etc.,

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6. Transpiration of tress and shrubs.

The roots of trees planted near the building may extent upto the foundation level, they may

penetrate through the joint and may absorb the moisture this effect is seen in the form of

depression on the ground and development of cracks in the masonry

To prevent such failure

Foundation should be taken sufficiently deep. (min 1 m )

Fast growing hard root trees and water seeking trees should not be planted near the

building with a minimum distance of 8 m.

7. Shrinkage due to withdrawal of moisture from the soil below the foundation.

This occur at place where there is a considerable variation in the height of water table,

when ground water table falls, there is a shrinkage of soil resulting in the crack to the

building.

To prevent such failure

Drive piles up to the hard soil.

Collapse the capillary of the soil.

II. DEEP FOUNDATION :

According to Terzaghi in case of deep foundation the depth is greater than the width of the

foundation.

The hard strata of good bearing capacity is not available nearer the ground surface, the

foundation of the structure as to be taken deep with the purpose of attaining the bearing

stratum which is suitable in all respect. Sometimes for ensuring stability and durability of

the structure deep foundation is required.

The most common type of deep foundation are

a. Pile foundation

b. Coffer dam foundation.

c. Caisson foundation.

PILE FOUNDATION :

Pile foundation is generally used for deep foundation when simple spread footing at a

suitable depth is not possible either because of hard strata of required bearing capacity is at

a greater depth of steep slopes are encountered. In that case pile foundation is

recommended.

Pile foundations are suitable for building bridges where hard strata is not available.

Types of Pile Foundations :

Pile foundations are mainly classified on the basis of the material used for constructionand based on theirfunction.

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Based on material used for construction :

a. Timber piles.

b. Concrete piles.c. R.C.C piles.

d. Steel piles.

e. Composite (or) compound piles.

Based on their function :

a. Bearing piles.

b. Friction piles.

c. Batter piles.

d. Anchor piles.

Bearing piles : This piles penetrate through the soft soil and their bottom rest on a

hard bed, thus they are end bearing piles and act as columns and

pears.

Friction piles : When piles are required to be driven at a site where the soil is weak

(or) soft to a considerable depth. The load carried by a pile is bear

by the friction developed between the lateral (side) faces of the pile

and the surrounding ground, such piles are called friction piles.

Timber piles : This piles are prepared from trunks of trees. Transmission of loads

through timber piles takes place by frictional resistance of the

ground and the pile surface (or) timber piles are also used as end

bearing piles.

Timber piles prove economical for supporting light structures to be located in compressive

soil constantly saturated with water. They may be circular (or) square in cross section,

they are driven by the help of pile driving machine. To prevent the pile head from

hammering the iron ring is provided at the top of the pile. To protect the lower end of the

pile at the time of driving a cast iron conical shoe is provided.

Advantages of timber piles.

1. They are economical.

2. This piles can be handled easily with little risk and danger of breakage.

3. They do not need heavy machinery and elaborate technical supervision.

4. The length of the timber pile can be easily adjusted either by cutting (or) lengthening

without much extra cost and risk.

5. Skilled supervision is not required in construction of timber piles.

6. This piles can be removed and insert easily if necessary.

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Disadvantage of timber piles.

1. This piles deteriorated due to the action of soil (or) water (or) insects.

2. This piles cannot be taken heavy loads.

3. It becomes very difficult (or) even impossible to drive the pile in hard formation.

4. It is difficult to get the timber pile required size and depth.5. Unless the timber piles are properly treated they are not durable and have short life

time.

Cement concrete piles

Cement concrete poses excellent compressive strength with the addition of reinforcement

with concrete called R.C.C piles are become more popular and these piles replaced other

piles rapidly R.C.C piles and cement concrete piles are divided into 2 groups ie.,

a. Pre-cast Piles

b. Cast-in-Situ Piles.

PRE-CAST PILES

These piles are cast and cured in the casting yard and then transported to the site for

drilling in case space is available for casting the pile near the site they can be cast and

cured there itself. When required they are driven in the similar manner as timber piles with

the help of pile drivers. They are moulded in circular, square, rectangle, octagonal form.

Advantages of pre-cast piles.

1. They can be cast well before the commencement of the work resulting in rapid

execution of work.

2. These construction can be well supervised and any defect can be rectified before

use.

3. The reinforcement remain in these proper position and do not yet displaced.

4. These piles can be directly driven under water.

5. They can be loaded soon after they have been driven to the desired depth.

Disadvantages

1. They are heavy and hence great difficulty for handing and transportation.

2. If sufficient care is not taken during the transportation and drilling the pile may

broke.

3. Extra lengthening of the pile can rarely be predetermined and as such it has to be

lengthening some times rendering the piles weak at the joint.

4. Some times the length of the piles is more than the required length in that case the

pile is shortened it becomes weak.

5. If the piles are not available at the required time then the delay of the work taken

place.

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CAST-IN-SITU PILES

This are those piles which are cast in position inside the ground. Since the pile is not

subjected to handling or divining stress cast-in-situ piles are further classified in to 2 types

that is with casing orwithout casing.

With casing : This piles is permanently left in place inside the ground.

Without casing : This casing of the piles are withdrawn from pile hole.

Advantages of cast-in-situ piles.

1. Light weight shells are used in cast-in-situ piles these are easy to handle and easy

to drive in the ground.

2. There is no wastage of material because the required length of the pile is

constructed.

3. No extra reinforcement is necessary to resist the stresses developing duringhandling and driving operations.

4. If the need arises additional pile may be cast (or) constructed quickly.

5. Extra cost of transport of pile is eliminated.

Disadvantages

1. It is difficult to maintain the reinforcement in correct position during construction

of piles.

2. These piles cannot be constructed under water.

3. It is not possible to have a proper control over the compaction and design of the

piles.

4. If the ground is dry it absorb moisture from the concrete before the concrete set, so

the pile become weak.

5. The placing of the concrete members cannot be inspired as such there is a

possibility of voids being left at the time of casting, rendering the construction

becomes unsound.

Note: Pneumatic caisson foundation, well foundation, Isolated foundation, Inverted

Arch foundation.

INVERTED ARCH FOOTING

This types of foundation is to be provided for multi storied building in earlier. After

investigating R.C.C construction inverted Arch footings is rarely constructed. One of the

draw back (or) disadvantages in this type of footing is the end piers have to be special

strengthened by buttresses to avoid Arch thrust tending to rapture the pier junction. The

advantage of inverted Arch foundation is that in soft soil the depth of the foundation is

considerably reduced.

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COFFER DAMS

Coffer dam is defined has temporary structure constructed in water barring areas such as

river, lakes, sewage water, etc., for excluding water from working spot. To enable smooth

going of construction operations.

The walls of the coffer dam should be practically water tight (or) at least they should beable to exclude water to such an extent that the quantity of water that leaks insides the

working spot and can be easily pumped out.

Coffer dams are classified according to types of construction are :-

1. Earthen coffer dam.

2. Rock fill coffer dam.

3. Single wall coffer dam.

4. Double wall coffer dam.

5. Cripps coffer dam.

6. Cellular coffer dam.a. Circular type.

b. Diaphragm type.

CAISSON FOUNDATION

Caisson is defined has a water tight structure made up of wood, steel (or) reinforced

concrete. Constructed in connection with excavation for foundation of bridges, piers,

abutments. Caisson remains in its position and ultimately become and integral part of the

permanent structure. They are mostly used for deep foundation under water, where the

foundation must extent upto (or) below the river bed.

Caisson are classified in to three types :

1. Open caisson.

2. Closed caisson (boxed caisson).

3. Pneumatic caisson.

OPEN CAISSON

It is a box type structure having no top (or) bottom mainly consists of vertical walls. This

caisson sinks due to its own weight when the soil from the space inside is removed by useof claim shell (or) any other method stage by stage. When the caisson is sunk to the

required depth its base is plugged by providing a thick layer of concrete. Open caissons

are single wall open caisson, cylindrical open caisson and open caisson with dredging

wall. Dredging wall caisson are being employed for deepest foundation for bridge pier,

apartments and other similar structures. This caissons are rectangular (or) square in shape

is further sub-divided into smaller section. The walls are normally made up of reinforced

concrete. This caisson is sunked by excavating soil through the wells by means of

dredges.

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CLOSED CAISSON (or) BOX CAISSON

This types of caisson are similar to open caisson accept that it is closed at bottom. The

caisson is sunked by filling sand, gravel concrete in the empty space inside. The space

where the caisson base is rest must be leveled. This types of caissons are used in place

where the strata of sufficient bearing capacity is available.

PNEUMATIC CAISSON

This type of caisson is closed at top and open at the bottom during the construction water

is excluded from the caisson chamber by means of compressed air. The working chamber

and the shaft are made air tight. The workmen may carry out excavation work below the

caisson and the water may not find its way inside from bottom. The pressure of the

compressed air in the shaft is just kept higher then that of the water at that depth. Each

caisson has two air locks through one air lock the working man enter for excavation

through other the excavated material is taken out. In this method of construction of

foundation is complicated, expensive and very slow but in some places, other type ofcaisson is not at all suitable. Pneumatic caisson appears to be only choice. The most

advantage of this method is that entire operation of sinking the caisson can be carried out

under controlled condition. This type of caisson is suitable depth ranging from 25m to

40m.

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UNDER REMMED PILES

Under rimed piles are usually cast-in-situ concrete piles (or) R.C.C piles having bulb

shaped enlargement (or) projection near the base, This piles are commonly recommended

for providing safe and economically foundation in expensive soil. Such has black cotton

soil, filled soil and other type of soil having poor bearing capacity. A pile having one bulb

is known as single under rimed pile. It is observed that the load bearing capacity of the

pile can be increased by increase in number of bulb at the base.

Composite Piles

This are the pile which are constructed by using two different materials are driven one

over the other so has to enable to act together to perform a function of a single.

Composite piles prove economical has they permit the utilization of grade corrosion

resistance property of one material with the strength of the other.

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Pile driving

Piles are insert in the ground by the following method.

a. By drop hammer.

b. By Steam hammer.c. By water jet.

d. By Boring.

The process of forcing a pile into the ground without excavation is termed has pile driving.

The pile should be driven vertically.

By drop hammer

It is a pile driver in which the hammer is raised by a rope (or) chain cable and dropped

over the head of piles vertically. The raise of weight and height of drop depends upon

condition of the soil and types of the piles.

By steam hammer

It is the advanced technology of drop hammer method in this the pile driver the hammer is

automatically raised and then dropped by means of a steam cylinder and piston. The frame

work supporting the hammer is also has pile lifting device on account of uniform steam

pressure the rate of hammer blow is uniform and continuous motion of piles took place.

By water jet

In this method of pile driving the displacement of the soil below the shoe of the pile by

means of one (or) more of water jet. The water jet coming out of nosed washes the soil

below the pile and the pile sinks down in to the hollow space.

By boring

If the pile is required to penetrate to the beds of hard soil (or) soft rock to reach its

required depth driving the pile by boring is on economical solution. In case of dry soil

augur boring is preferred and is case of soft rocks rotary well driller is preferred. In the

prepared bore pre-cast pile is inserted. In case of continuously stiff soil site-in-piles may

be suitable.

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GENERAL INSPECTION OF SITE

The general inspection of site of work serves has a good guide for determining the type of

foundation to be adopted for the proposed work.

It helps in getting the data with respect to the following items.

a) Behavior of ground due to variation in water table.

b) Disposal of storm water at site.

c) Displacement of soil due to the weight.

d) Nature of soil.

e) Moment of ground due to any reason.

Methods of site exploration (or) examination of ground

1. Trial pit (or) test pit.2. Propping.

3. Boring.

a) Augur boring.

i. Screw augur.

ii. Slit augur.

iii. Shell augur.

b) Wash boring.

BEARING CAPACITY OF SOIL (load)

The ultimate capacity (or) load on the soil from the structure is coming on soil and hence

it is almost important to know the strength and behavior of soil.

The maximum load per unit area which the soil resist (oppose) safely without

displacement is called bearing capacity of the soil

S.B.C Safe Bearing Capacity

It is defined as the ratio of ultimate bearing capacity to factor of safety

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Method for determination of Bearing capacity

1. Method of loading.

2. Method of dropping weight.

Method of Loading

A square pit of required size is excavated upto the required depth. The side of the pit

should be at least 5 times the side of steel plate. At the bottom of the pit a square hole is

excavated at the center of size equal to the steel plate. The bottom of the hole should

corresponding to the foundation level and the ratio of depth (d1) to breadth (b1) of the

pit may be equal to the ratio of depth (d2) and width (b2).

The steel plate is put up in the hole and then the platform is prepared as shown in the fig.

The amount of initial load is decided on the bases of bearing capacity of that particular soil

and also dead weight of the testing component should be work out carefully.

A dumpy level is planted to note the settlement of the steel plate with reference to the

bench mark. The load is to keep on the platform till the settlement of the soil stops. Then

the load is increased by a suitable amount usually 0.5 t (500 kgs) at a time and note downthe settlement reading till the settlement stops.

The bearing capacity of soil is calculated as follows :

Bearing capacity of soil is calculated as follows :

B.C of soil in t = weight / area of steel plate.

Safe bearing capacity (S.B.C) = Bearing capacity / Factor of safety (B.C / F.O.S)

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Method of dropping weight

This is the simple and approximate method to find bearing capacity of soil. A square pit is

excavated of required size upto the required depth of foundation. A known weight is

dropped from the top of the pit at the center. The weight made an impression at the bottom

of the pit of depth `D.

The resistance of the soil R = (W x h) / d.

The resistance of the soil per unit area = R/A = B.C of soil / per unit area.

Therefore S.B.C of soil = R / A x F.O.S

Where, R is the resistance of soil.

H is the height of the weight.

d is the depth of depression.

W is the weight of the substance.

A is the cross sectional area of substance.

The result obtained by this method are approximate and hence this method is used for

minor engineering structures.

Method of improving bearing capacity of soil

1. Increase the depth and width of footing is the simplest method of increasing the

bearing capacity.

2. Drainage is a well known method to improve the bearing capacity for some soil.

3. Ramping granular materials like sand, gravel, stone dust to the natural soil.

4. By driving sand piles.

5. By confining the soil in the enclosed area by driving sheet piles.6. By grouting cement slurry, cement mortar (or) chemicals to collapse voids and

capillarity.

Properties of soil and its application

Soil The term soil has various meaning depending upon their general professional field

in which it is being considered.

To an engineering soil is unaggregated un-cement deposit of minerals (or) organic

particles (or) fragmentation covering large portion of the earth crust.

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Classification of Soil

According to engineering purpose soil is mainly classified into two groups :

1. Coarse soil.

2. Fine soil (or) fine aggregate.

Coarse soil : The portion of the soil particles greater than 4.75mm retained on 4.75 sieve

is called coarse particles (or) coarse aggregate.

Fine aggregate : The soil particles less than 4.75 mm (passes through 4.75mm and retain

on 0.075 mm is called fine aggregate). The particle size less then 75

micron (< 0.075mm) is called silt and clay particles.

Properties of Soil

Specific gravity of soil : It is defined has the ratio of weight of a given volume of a soilto the weight of a equal weight of water at a constant

temperature.

G =

Water contain (w) : It is also called has moisture content. It is defined has the ratio

of weight of water to the weight of soil in a given mass.

W =

Bulk density : It is defined has the ratio weight of a soil to its volume.

Dry density : It is defined has the weight of dry soil per unit of volume of the

soil.

Sub merged density : It is defined has the ratio of weight of sub merged soil to thevolume of the soil.

Void ratio (e): It is defined has the ratio of a volume of voids to the volume of

soil.

Porosity (n) : It is defined has the ratio of volume of voids to the total volume

of given soil.

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Permeability : It is defined has a property of a porous material which permit th

passage (or) seepage of water (or) any other fluids through its

inter connecting voids.

Compaction : Compaction is a process by which the soil particles are artificial

re-arranged and packed together into a closer state of contact bymechanical means in order to decrease the porosity (void ratio)

and increase its dry density.

Shear strength of soil : It is the resistance to deformation by continuous displacement of

soil particles upon the action of shear stress.

Consistency : It is the degree of fineness of the soil.

Consistency limit : Consistency limits are the water content at which the soil mass

passes from one state to the other are

1) Liquid limit.2) Plastic limit.

3) Shrinkage limit.

Liquid limit (W L) It is defined has the minimum water content at which the soil is

still in the liquid state.

Plastic limit (W p) It is defined has the minimum water content at which a soil is in

plastic condition.

Plastic limit (W s) It is defined has the lowest water content at which soil can still

be completely saturated.

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