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CHAPTER 5

EXPERIMENTAL SETUP AND PROCEDURES

5.1 GENERAL

The experimental setup and procedures for conducting various tests

on concrete and RCC elements are discussed here.

5.2 EXPERIMENTAL SETUP FOR CONCRETE SPECIMENS

5.2.1 Concrete and Mortar Cubes

The size of mortar cubes used for this investigation was 70.6 x 70.6

x 70.6 mm confirming to IS 10080-1982. Compressive strength of mortar

cubes were found according to IS: 4031-1982 (Part 6). Similarly, to determine

the compressive strength and durability effects of concrete,

150 mm × 150 mm × 150 mm size concrete cubes were cast and tested in

accordance with IS: 516-1959. All strength tests were conducted using

2000kN compression testing machine. Cube moulds of size 150x150x150 mm

were used. They were cleaned thoroughly using a waste cloth and then

properly oiled along its faces. Concrete was then filled in mould and then

compacted using a standard tamping rod of 60 cm length having a cross

sectional area of 25mm2. Concrete mixtures with different proportions of

copper slag ranging from 0% to 60% replacement for sand and 0% to 20% for

cement were prepared and tested.

55

5.2.2 Concrete Cylinders

The size of cylinder used for split tensile strength and durability

studies was 150mm diameter and 300mm height. This test was conducted in

accordance with IS: 5816-1999. The crude oil was applied along the inner

surfaces of the mould for the easy removal of specimens from the mould.

Concrete was poured throughout its length and compacted well.

For corrosion test, 12mm diameter bars of Fe 250 grade of steel

were embedded at the centre of the specimens with 70mm cover thickness.

5.2.3 Concrete Discs

Disc shaped specimens of nominal size 100mm diameter x 50mm

thickness was used to carry out RCPT test in concrete in accordance with

ASTM C-1202. Moulds are made by using PVC. The crude oil was applied

earlier along the inner surfaces of the mould for the easy removal of

specimens from the mould.

5.2.4 Concrete Beams

Concrete beams of standard size 750 x 150 x 150 mm confirming to

IS: 516-1959 was used for this study. A total number of 21 specimens were

cast for different proportions of copper slag with sand in each series. Out of

which, three specimens were treated as controlled specimens. Seven test groups

were constituted with replacement of 0% (control specimen), 10%, 20%, 30%,

40%, 50% and 60% copper slag with sand in each series. Three specimens

were prepared for every replacement percentage and these beams were tested

for flexural strength in Universal Testing Machine of capacity 100 tonnes.

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5.3 EXPERIMENTAL SETUP FOR RCC SPECIMENS

5.3.1 RCC Beams

Two types of RCC structural elements have been considered for

study.

They are:

• Flexural behaviour of RCC beams incorporating copper slag

as partial replacement of sand. (Replacement – 0 to 60%)

• Flexural behaviour of RCC beams incorporating copper slag

as partial replacement of cement (Replacement - 0 to 20%)

Simply supported RCC beams were subjected to pure flexural

failure by subjecting them to two point loading test. The beams used in this

study were 150mm x 150mm in cross section and 1500mm in length. Two

10 mm diameter bars were used for flexural reinforcement at bottom and two

8 mm rods were provided for top reinforcement. For each beam, 6 mm

diameter mild steel bars are used as stirrups, spaced 100 mm c/c for shear

reinforcement. Typical beam reinforcement details are illustrated in

Figure 5.1. For this investigation, a total number of 36 beam specimens were

cast and tested for sand and cement replacement (18Nos. - sand replacement,

12Nos.-cement replacement, 3Nos. - combined replacement and 3Nos.-

controlled specimens). All beams were cast by using M20 grade concrete with

20 mm size of CA, locally available sand and OPC 43 grade cement.

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Figure 5.1 Beam reinforcement details

5.3.1.1 Experimental set up of RCC beam

All beams (150mm x 150mm in cross section and 1500mm in

length) were tested as simply supported beams under two point loading over

an effective span of 1400mm. The loads were applied at a distance of 470mm

on either side of the mid span of the beams of 1500mm length, as shown in

Figure 5.2. To study the performance of copper, slag replaced specimens.

These beams were tested in a loading frame of 500 kN capacity. The loads

were monitored through a high accuracy load cell with a load sensitive of 0.1

tonnes. For this case, mid span deflection was measured using dial gauges of

least count 0.01mm. The parameters such as initial cracking load, ultimate

load and the deflected shape of the specimens were noted.

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Figure 5.2 Experimental set up of RCC beams

5.3.2 RCC Short Columns

To find axial compressive strength, columns with square cross

section of size 100mm x 100mm cross section and 1000mm long were used.

The head was provided at each end of columns with the size of 140mm x

100mm x100mm to avoid crushing failure. All the columns were provided

with four 8mm diameter Tar steel Fe 415 as longitudinal and 6mm diameter

mild steel rods Fe 250 as transverse reinforcement with spacing of 100mm

centre-to-centre distance. A 20mm effective cover for reinforcements was

provided. L/D ratio maintained for this type of column was 10. A total

number of 21 specimens were cast for different proportions of copper slag

with sand in each series. Three specimens were treated as controlled

specimens. The reinforcement details of the columns are shown in Figure 5.3.

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Figure 5.3 Reinforcement details of short columns

5.3.2.1 Experimental set up of RCC short columns

All the columns were tested under pure axial compressive load. The

columns were tested in a column tester of 2000 kN capacity. The load was

applied gradually in a controlled manner in increments of 2kN by hand

pumping of the manually operated hydraulic jack. The loading was monitored

through a high accuracy load cell with a sensitivity of 1kN. The axial strain

values were measured from the compressometer positioned at mid height of

column for various loads taken from the proving ring. The lateral

deformations were measured by dial gauges of least count 0.01mm fixed at

adjacent faces of the columns as shown in Figure 5.4. The parameters such as

initial cracking load, ultimate load and the deflected shape of the specimens

were noted.

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Figure 5.4 Experimental set up of RCC short columns

5.3.3 RCC Long Columns

The following types of columns have been considered for

investigation of failure due to buckling.

• Buckling behaviour of RCC long columns incorporating

copper slag as partial replacement of sand. (Replacement - 0

to 60%)

• Buckling behaviour of RCC long columns incorporating

copper slag as partial replacement of cement (Replacement - 0

to 20%)

To find axial compressive strength, columns with square cross

section of size 150mm x 150mm cross section and 1900mm long were used.

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The head was provided at each end of columns with the size of 240mm x

200mm x175mm to avoid crushing failure. L/D ratio maintained for this

column was 12.67. Therefore, this column is otherwise called long columns.

All the columns were provided with four 10mm diameter Tar steel Fe 415 as

longitudinal and 6mm diameter mild steel rods Fe 250 as lateral ties for

transverse reinforcement with spacing of 100mm centre-to-centre distance.

These column specimens were cast by using specially fabricated steel moulds.

The details of the geometry of the column specimens and details of

reinforcement used for the specimens are shown in Figure 5.5. For this

investigation, a total number of 36 column specimens were cast and tested for

sand and cement replacement (18Nos. - sand replacement, 12Nos.-cement

replacement, 3Nos. - combined replacement and 3Nos.-controlled specimens).

Figure 5.5 Reinforcement details of RCC long columns

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5.3.3.1 Experimental set up of RCC short columns

All the columns were tested under pure axial compressive load. The

columns were tested in a column tester of 2000 kN capacity. The load was

applied gradually in a controlled manner in increments of 2kN by hand

pumping of the manually operated hydraulic jack. The loading was monitored

through a high accuracy load cell with a sensitivity of 1kN. The lateral

buckling deformations were measured by LVDTs of least count 0.01mm fixed

at adjacent faces of the columns at mid span as shown in Figure 5.6. The

parameters such as initial cracking load, ultimate load and the deflected shape

of the specimens were noted. Cracks formed on the surfaces were marked and

identified. The load and deflection characteristics were studied.

Figure 5.6 Experimental up of RCC long set columns

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5.4 EXPERIMENTAL PROCEDURES

5.4.1 Compressive Strength Test

Concrete cubes of size 150mm×150mm×150mm were cast with

and without copper slag. During casting, the cubes were mechanically

vibrated using a table vibrator. After 24 hours, the specimens were demoulded

and subjected to curing for 28 days in portable water. After curing, the

specimens were tested for compressive strength using compression testing

machine of 2000KN capacity. The maximum load at failure was taken. The

average compressive strength of concrete and mortar specimens was

calculated by using the following equation 5.1.

Ultimate compressive load (N)

Compressive strength (N/mm2) = (5.1)

Area of cross section of specimen (mm2)

The tests were carried out on a set of triplicate specimens and the

average compressive strength values were taken.

5.4.2 Split Tensile Strength Test

Concrete cylinders of size 150 mm diameter and 300mm length

were cast with incorporating copper slag as partial replacement of sand and

cement. During casting, the cylinders were mechanically vibrated using a

table vibrator. After 24 hours, the specimens were demoulded and subjected

to curing for 28 days in portable water. After curing, the cylindrical

specimens were tested for split tensile strength using compression testing

machine of 2000kN capacity. The ultimate load was taken and the average

split tensile strength was calculated using the equation 5.2.

2P

Split tensile strength (N/mm2) = (5.2)

Π LD

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where,

P=Ultimate load at failure (N),

L=Length of cylindrical specimen (mm),

D=Diameter of cylindrical specimen (mm).

The tests were carried out on a set of triplicate specimens and the

average tensile strength values were taken.

5.4.3 Ultrasonic Pulse Velocity Test

This test was conducted as per the procedure given in IS:

13311:1992. Ultrasonic Pulse Velocity (UPV) is a non-destructive technique

that measures involves measuring the speed of sound through materials in

order to predict material strength, to detect the presence of internal flaws such

as cracking, voids, honeycomb, decay and other damage. The instrument

consists of a transmitter and a receiver (two probes). The time of travel for the

wave to pass from the transmitter to the receiver when kept opposite to each

other is recorded in the ultrasonic instrument (Limaye 2002). The distance

between the two probes (path length) was physically measured. Hence,

Ultrasonic Pulse Velocity = Path length / Transit time (5.3)

This velocity is related to its compressive strength. The quality and

approximate compressive strength of concrete was determined by using

Table 5.1 which gives the relationship between ultrasonic pulse velocity and

quality of concrete as per IS: 13311:1992.

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Table 5.1 Relationship between ultrasonic pulse velocity and quality of

concrete as per IS: 13311:1992

Longitudinal pulse

velocity km/sec

Approximate

compressive strength

N/mm2

Quality of

concrete

Below 2.0 --- Very poor

2.0 to 3.0 4.0 poor

3.0 to 3.5 Upto 10 Fairly good

3.5 to 4.0 Upto 25 good

4.0 to 4.5 Upto 40 Very good

Above 4.5 > 40 Excellent

5.4.4 Open Circuit Potential (OCP) Test

The standard test is given in ASTM C 876 and is illustrated in

Figure 5.7. The apparatus includes a copper-copper sulphate half-cell,

connecting wires and a high impedance voltmeter. The positive terminal of

the voltmeter is attached to the reinforcement and the negative terminal is

attached to the half-cell. A high impedance voltmeter is used so that very little

current runs through the circuit. The half-cell makes electrical contact with

the concrete by means of a porous plug and a sponge moistened with a wet

solution (such as liquid detergent). Cylindrical reinforced concrete specimens

of size 100mm diameter and 300 mm height were cast in triplicate with

various replacement percentages of copper slag with sand and cement. For

this investigation, 12mm diameter of Fe 250 TMT bars are embedded into the

concrete with cover thickness of 60mm. All the triplicate specimens were

taken out and then dried. The potential of the embedded rebar was measured

against saturated calomel electrode (SCE) using a high impedance voltmeter

before keeping the specimens in 3.5% of NaCl solutions. Then, the specimens

were subjected to alternate wetting (5 days) and drying (5 days) in 3% NaCl

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solutions in order to induce accelerate corrosion. The potential readings were

measured periodically (Nicholas 1999). The experiment is continued for a

period of 90 days. Potential measurements were carried out at an ambient

temperature of 32+1°C. Table 5.2 shows the relationship between potential

values and probability of corrosion.

Figure 5.7 OCPT test apparatus

Table 5.2 Relationship between for OCP values and probability of

corrosion

OCP values

(mV vs. SCE)

Corrosion condition as per

ASTM C876-1995

< -426 Severe corrosion

< -276 High (90% risk of corrosion)

-126 to -275 Intermediate corrosion risk

> -125 Low(10% risk of corrosion)

5.4.5 Accelerated Corrosion Process: Gravimetric Weight Loss Method

This investigation was carried out as per ASTM G1-90. The weighed

TMT steel specimens were embedded in concrete cylinder of size 150mm

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diameter and 300 mm height. The reinforced concrete samples (Figure 5.8) were

subjected to alternate wetting and drying exposure in 3.5% NaCl solution.

Regular D.C power supply of 12V is supplied continuously throughout the

corrosion period of 15 days. Positive terminal of voltmeter is connected with

soldered wires and negative terminal is connected with copper plate (cathode).

After the process of accelerated corrosion, all the specimens were disconnected

and removed from tank. After the corrosion period, the rod was taken out and

weighed. The loss in weight was calculated. From the weight loss values,

(ASTM G-1) the corrosion rates were obtained from the relationship

(K * W )

Corrosion rate = mm/yr (5.4)

(A*T*D)

where K is a constant, K =87.6 in case of expressing corrosion rate in mm/yr

T is the exposure time expressed in hours,

A is the surface area in cm2, W is the mass loss in milligram and

D is the density of the corroding metal (7.85g/cm3)

Figure 5.8 Reinforced concrete samples for corrosion test

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5.4.6 Rapid Chloride Penetration Test

Concrete disc specimens of size 100mm diameter and 50mm thick

(Figure 5.9) were cast for various replacement percentages of sand and

cement with copper slag in concrete. After 24 hours, the disc specimens were

removed from the mould and subjected to curing for 90 days in chloride free

distilled water. After curing, the specimens were tested for chloride

permeability. All the specimens were dried free of moisture before testing.

Figure 5.9 Concrete disc specimen for RCPT test

The test set up is called Rapid Chloride Penetration Test (RCPT)

assembly. This is two-compartment cell assembly. Disk specimen is

assembled between the two compartments cell assembly and checked for air

and watertight. The cathode compartment is filled with 3%NaCl solution and

anode compartment is filled with 0.3 normality NaOH solutions. Then, the

concrete specimens were subjected to RCPT by impressing a 60V from a DC

power source between anode and cathode. Current recorded over a period of 6

hours at an interval of 30 minutes as per the procedure given in ASTM C1202

(Table 5.3). This test was conducted at CECRI, Karaikudi, Tamil Nadu.

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Table 5.3 Charge passed through RCPT test as per ASTM C1202

S.No Charge passed

coulombs

Chloride ion

penetrability

1 >4000 High

2 2000-4000 Moderate

3 1000-2000 Low

4 100-1000 Very low

5 <100 Negligible

From the current values, the chloride permeability is calculated in

terms of coulombs at the end of 6 hours by using the following equation 5.5.

Q= 900 (I0 + 2I30 + 2I60 + 2I90 + …………. + 2I300 + 2I330 + 2I360) (5.5)

where,

Q = Charge passed (Coulombs)

I0 = Current (amperes) immediately after voltage is applied

It = Current (amperes) at t minutes after voltage is applied

5.4.7 Water Absorption Test

The water absorption values for various mixtures of concrete were

determined on 150mm x 150mm x 150mm cubes as per ASTM C 642. The

specimens were taken out of curing tank at 56 days to record the water

saturated weight (Ws).The drying was carried out in an oven at a temperature

of 105°c. The drying process was continued until the difference between two

successive measurements agreed close. Oven-dried specimens were weighed

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after they cooled to room temperature (Wd). Using these weights, saturated

water absorption (SWS) was calculated. The formula used to find water

absorption value of concrete specimens is given in equation 5.6.

SWA= [ (Ws-Wd) / Wd ] × 100 (5.6)

where,

SWA - Saturated Water Absorption in percentages

Ws - Weight of the specimen at fully saturated condition in kg,

Wd - Weight of oven dried specimens in kg.

5.4.8 Acid and Sulphate Resistance Test

Concrete cubes of size 150mm x 150mm x 150mm were cast and

stored in a place at a temperature of 27°C for 24 hours and then the specimens

were water cured for 28 days. After 28 days of curing, the specimens were

taken out and allowed to dry for one day. Weights of the cubes were taken.

For acid attack, 5% of dilute sulphuric acid (H2So4) by volume of the water

with ph value of about two was used. After that, cubes were immersed in the

above said acid water for a period of 30 - 60 days.

For sulphate attack, 5% sodium sulphate (Na2So4) and 5%

magnesium sulphate (MgSo4) by weight of water was added. The specimens

were kept for alternate wet and dry tests and were repeated for 30 cycles. The

concentration of the solution was maintained throughout this period by

changing the solution periodically. The specimens were taken out from acid

and sulphate solution at 30& 60 days. The surface of the cubes were cleaned,

weighed and tested in the compression testing machine.

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5.4.9 X-ray Diffraction Test

X-ray diffraction measurement is a method for measuring

characteristics, diffraction angles and intensities from randomly oriented

powder crystallites irradiated by a mono chromate X-ray beam.

Concrete cubes of size 150mm x 150mm x 150mm were cast and

cured in curing tank. After a curing period of 28 days, cubes were tested on

compression testing machine. After testing, samples were collected and

powdered in ball mills to pass through the sieve size of 75µ. The powder was

collected from the replacement 0f 0%, 5%, 10%, 15%, 20% of copper slag

with cement and 20%, 40%, 60% of copper slag with sand in each series. A

powdered specimen is usually prepared and packed in a specimen holder

made of aluminum or glass. The powder was tested at CECRI in Karaikudi,

Tamil Nadu.

5.4.10 Direct Shear Test

The soil is taken in a shear box of size 60 x 60 x 25 mm. The soil is

compacted while filling the laminar box. The base plate is attached to the

lower half of the box. A porous stone is placed in the box. A plain grid is

placed on the porous stone, keeping its segregations at right angles to the

direction of shear. The upper grid, porous stone and the pressure pad are

placed on the specimen. The box is placed inside the large container and

mounted on the loading frame. The upper half of the box is brought in contact

with the proving ring. The dial gauge is fitted to the container to give the

shear displacement. The locking pins are removed. The normal load is applied

to give a normal stress of 0.1Kg/cm2.Shear load is then applied at a constant

rate of strain which is generally between 1mm to 2mm per minute. The test is

continued till the specimen fails. The failure is indicated when the proving

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ring dial gauge begins to recede after having reached the maximum. The

following equation 5.7.

In proving ring, 575 divisions = 100Kg

Shear force at failure = (proving ring reading/575) x 100

Ultimate shear stress = shear force at failure / area of shear box

τ = σ x tan (φ) (5.7)

where,

τ = Shear stress in kg/cm2

σ = Normal stress in kg/cm2

and

φ = Angle of internal friction

5.4.11 Triaxial Shear Test

Triaxial Shear test was used to determine the Angle of internal

friction, shear strength parameters and young’s modulus of Copper Slag. A

non-porous cap was put on the bottom pedestal and the rubber membrane

slide over it and ties it with the bottom pedestal of the base by O-ring. The

split mould was put over the base and the rubber membrane taking through it

inside and stretches over it at the top. Then soil is weighed in a dish to make a

sample of required dry density. For dense samples pour the sample in the

mould in layers and compact it by tamping without rupturing the membrane.

After the required weight of sample has been used, level the top, place the

solid cap over it and seal by O-rings. Then, operate the vacuum and carefully

remove the split mould without jarring the sample. Assemble the cell and fill

it with water to exert a confining pressure of the order of 5 N/cm2.The loading

plate-form of the compression machine was raised to bring the ram in contact

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with the loading cap. Zero adjustment was made on dial gauge to compensate

for the load due to cell pressure and piston friction. Additional stress was

added to the triaxial cell and the displacement values of specimens were taken

directly from the digital indicator which is fixed at control panel. The

following shear strength parameters has been observed (equations 5.8) from

the above triaxial shear test.

Original area of

specimen A0 = σ1–σ3

Corrected area Ac = A0/1-ξ

Strain ξ = ∆L/L0

Axial stress σ1 =σ3 tan2

(450+φ/2) + 2C tan (45

0+φ/2)

θf = 450+φ/2 (5.8)

where,

A0 = Original Area in mm2

Ac = Corrected Area in mm2

ξ = Strain

∆L = Change in Length in mm

L0 = Original Length in mm

Φ = Angle of internal friction

σ1 = Axial stress in kg/cm2

σ3 = All round pressure in kg/cm2 and

θf = Angle of Shear failure plane in degrees

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5.5 SHAKE TABLE TEST (SPECIFICATIONS AND

PROCEDURES)

5.5.1 Shake Table with DC Motor Control

The shake table consists of a flywheel, a camshaft, a vibration table

and user designed cams. The maximum payload capacity of shake table is

30kg and the table has the dimension of 400mm x 300mm. The dimension of

circular mounting plate is 390mm. The variable speed DC motor, having

power of 1 H.P is used. The cam is connected to a variable speed DC motor

with a help of a camshaft. The frequency range of the cam is 0 to 25Hz and

the allowable frequency rang as ± 1.0mm.

5.5.2 Signal Conditioning Amplifier

Signal conditioning amplifier which is suitable for accelerometer

was used. It contains four channels with analog output and connected to the

Data Acquisition System. The signal conditioning amplifier operates on 230V

supply and has inbuilt excitation supply for the accelerometers and individual

signal conditioning circuits for all 4 channels.

5.5.3 Accelerometers

The high sensitivity accelerometers have the acceleration range of

+4g to -4g was used. It can measure for higher frequency upto 100 Hz.

5.5.4 Oscilloscope

A four channel digital storage oscilloscope is used to read and store

the acceleration values upto 60 MHz frequency.

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5.5.5 Data Acquisition System

In this data acquisition system, accelerometer with digital vibration

meter of size 15mm is used. One can measure velocity, acceleration, RMS

value, peak value, data hold, maximum and minimum value. The velocity

range is 20 and 200mm/s, the acceleration range is 200 and 2000m/s and the

frequency range is 40Hz-1 KHz.

5.5.6 Construction of Laminar Box and Retaining Wall Model

The models of retaining walls were built in a flexible laminar box

to considerably reduce the boundary effects. A laminar box is a large-sized

shear box consisting of several frictionless horizontal layers. The laminar box

used for this investigation is rectangular in cross section with inside

dimensions of 125mm x 250mm and 200mm deep with 15 rectangular hollow

aluminium layers, machined such that the friction between the layers is

minimum. The layers are separated by linear roller bearings arranged to

permit relative movement between layers in the long direction with minimum

friction. The gap between the successive layers is 1mm and the bottom most

layer is rigidly connected to the solid aluminium base plate of size 150mm x

300mm in plan and 15mm thickness.

An aluminium retaining wall was constructed inside the laminar

box and fixed approximately one third distance from left end of laminar box.

The height of the retaining wall is 120 mm. Figure 5.10 shows the

experimental setup for shake table test. A1, A2, A3 are accelerometers fixed

at backfill near retaining wall. Oscilloscope is used to record the acceleration

in terms of sine and cosine waves. This model was constructed based on

Madhavi Latha et al 2007 IISC, Bangalore Laminar box model (Figure 5.11).

Here copper slag has been used as backfill material in retaining wall and

replaced with various percentages of sand. The accelerations and

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displacement characteristics of retaining wall were found by conducting shake

table test.

Figure 5.10 Experimental setup for shake table test

Figure 5.11 Shake table with laminar box and retaining wall model

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5.5.7 Lateral Earth Pressure

There are three types of lateral earth pressure (Figure 5.12) acting

on retaining walls such as,

i) At Rest Earth Pressure

The at rest earth pressure develops when the wall experiences no

lateral movement. When the wall is at rest and the material is in its natural

state then the pressure applied by material is known as Earth Pressure at Rest.

When the retaining wall is at rest then the ratio between the lateral earth

pressure and the vertical pressure is called the co-efficient of the earth

pressure at rest,

Ko= (1-sinφ)

ii) Active Earth Pressure

The active earth pressure develops when the wall is free to move

outward. When the wall moves away from the backfill, there is a decrease in

the pressure on the wall and this decrease continues until a minimum value is

reach after which there is no reduction in the pressure and the value will

become constant. This kind of pressure is known as active earth pressure.

When the retaining wall is moving away from the backfill the ratio between

lateral earth pressure and vertical earth pressure is called coefficient of active

earth pressure,

Ka = (1-sinφ)/( 1+sinφ).

iii) Passive Earth Pressure

If the wall moves into the soil, passive pressure develops. When the

wall moves towards the backfill, there is an increase in the pressure on the

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wall and this increase continues until a maximum value is reach after which

there is no increase in the pressure and the value will become constant. This

kind of pressure is known as passive earth pressure. This means that when the

wall is about to slip due to lateral thrust from the backfill, a resistive force is

applied by the soil in front of the wall. When the retaining wall is moving

towards the backfill, then the ratio between the lateral earth pressure and the

vertical earth pressure is called the Coefficient of passive earth pressure,

Kp=(1+sinφ)/( 1-sinφ).

Figure 5.12 Types of lateral earth pressure

Therefore lateral earth pressure is the pressure that soil exerts in the

horizontal plane. A lateral earth pressure behind the wall which depends on

angle of internal friction (Φ), cohesive strength (c) of the retained material

and the direction and magnitude of movement. Lateral earth pressures are

typically smallest at the top of the wall and increase toward the bottom. The

equations 5.9 and 5.10 was used to find lateral earth pressure on backfill soil.

In this research, lateral earth pressure acting on retaining wall due to copper

slag addition as backfill, was found.

79

Ka = (1 - sinφ) / (1 + sinφ) (5.9)

P a = 1/2 * Ka * γ * H2

(5.10)

where,

γ = Unit Weight of Material in kN/m3

H = Height of the Wall in m

Ka = Earth pressure coefficient

φ = Angle of internal friction

Pa = Total active earth pressure of the wall in kN/m