report-direct shear test 1

Geotechnical Engineering Laboratory Group 4

DIRECT SHEAR TEST

1.0 OBJECTIVE

To determine the parameter of shear strength of soil, cohesion,C and angle of

friction,ϕ.

2.0 LEARNING OUTCOME

At the end of this experiment, students are able to :

Determine the shear strength parameter of the soil

Handle shear strength test, direct shear test

3.0 THEORY

The Direct Shear Test is used for determination of the consolidated drained (or

undrained) shear strength of soils. The test is performed by deforming a specimen at a

controlled rate on or near a single shear plane. The direct shear test is a laboratory testing

methods used to determine the shear strength parameters of soil. The test can be carried out

at different moisture contents; however, it is common to saturated the sample before running

the test. To achieve reliable results, the test is often carried out on three or four samples of

undisturbed soil. The soil sample is placed in a cubic shear box composed of a upper and

lower box. The limit between the two parts of the box is approximately at the mid height of

the sample.

The sample is subjected to a controlled normal stress and the upper part of the sample is

pulled laterally at a controlled strain rate or until the sample fails. The applied lateral load

and the induced strain are recorded at given internals. These measurements are then used to

plot the stress-strain curve of the sample during the loading for the given normal stres

Results of different tests for the same soil are presented in a chart with peak stress on

horizontal axis and normal (confining) stress on the vertical axis. A linear curve fitting is


often made on the test result points. The intercept of this line wit the vertical axis gives the

cohesion and its slope gives the peak friction angle. The shear strength is one of the most

important engineering properties of a soil, because it is required whenever a structure is

dependent on the soil’s shearing resistance.

The direct shear test is one of the oldest strength tests for soils. In this laboratory, a direct

shear device will be used to determine the shear strength of a cohesionless soil (i.e. angle of

internal friction (f)). From the plot of the shear stress versus the horizontal displacement, the

maximum shear stress is obtained for a specific vertical confining stress. After the

experiment is run several times for various vertical-confining stresses, a plot of the maximum

shear stresses versus the vertical (normal) confining stresses for each of the tests is produced.

The general relationship between maximum shearing resistance,τf and normal stress, σn

for soils can be represented by the equation and known as Coulumb’s Law :

τf = c + σ tan ϕwhere :

c = cohesion which is due to internal forces holding soil particles together in solid

mass

ϕ = friction which is due to the interlocking of the particles and the friction between

them when subjected to normal stress.

The friction components increase with increasing normal stress but the cohesion components

remains constant. If the is no normal stress the friction disappears. This relationship shown in

the graph below. This graph generally approximates to a straight line, its inclination to the


horizontal axis being equal to the angle of shearing resistance of the soil, ϕ and its intercept (

shear stress ) axis being the apparent cohesion, denoted by c.

4.0 TEST EQUIPMENT

i. Shear box carriage

ii. Loading pad

iii. Perforated plate


iv. Porous plate

v. Retaining plate


5.0 PROCEDURES

1. By using vernier calipers for verify internal measurement. L for the length of the sides

and B for the overall depth.

2. The shear box must fix base plate inside. Porous plate must put then on the base plate.

Perforated grid plate must be fix over porous so that the grid plates should be at right

angles to the direction shear.

3. Two halves of the shear box by means of fixing screws must fixed.

4. Transfer the soil sample from the square specimen cutter to the shearbox by pressing

down on the top grid plate for cohesive soils. The compact soil in layers to the required

density in shear box for sandy soil.

5. The shear box assembly on the loading frame must be mount.

6. The dial of the proving ring to zero must be setted.

7. The loading yoke on the loading pad must placed and the hanger onto the top of the

loading yoke must be carefully lift.

8. The correct loading to the hanger pad must be apply.

9. Remove the screws clamping the upper half to the lower half with carefully.

10. The test by applying horizontal shear load failure must be conducted. Rate strain should

be 0.2mm/min.

11. The reading of horizontal must be record and dial gauges at the regular intervals must be

force.

12. The test on the three identical soil samples under different vertical compressive stresses,

1.75kg, 2.5kg and 3.25kg must be conducted.

6.0 CALCULATION EXAMPLE

Specimen No. : 1 Loading : 1.75kg



Displacement Proving Ring Shear Stress(kN/m²) Strain

Dail Gauge ΔL (mm) Dail Gauge Load, P (kN)

20 0.04 10 0.0875 24.31 0.0006740 0.08 15 0.1313 36.46 0.0013360 0.12 20 0.1750 48.61 0.0020080 0.16 35 0.3063 85.07 0.00267100 0.20 40 0.3500 97.22 0.00333120 0.24 41 0.3588 99.65 0.00400140 0.28 42 0.3675 102.08 0.00467160 0.32 43 0.3763 104.51 0.00533180 0.36 44 0.3850 106.94 0.00600200 0.40 45 0.3938 109.38 0.00667220 0.44 47 0.4113 114.24 0.00733240 0.48 48 0.4200 116.67 0.00800260 0.52 50 0.4375 121.53 0.00867280 0.56 51 0.4463 123.96 0.00933300 0.60 51 0.4463 123.96 0.01000320 0.64 53 0.4638 128.82 0.01067340 0.68 53 0.4638 128.82 0.01133360 0.72 54 0.4725 131.25 0.01200380 0.76 55 0.4813 133.68 0.01267400 0.80 55 0.4813 133.68 0.01333420 0.84 56 0.4900 136.11 0.01400440 0.88 57 0.4988 138.54 0.01467460 0.92 58 0.5075 140.97 0.01533480 0.96 58 0.5075 140.97 0.01600500 1.00 59 0.5163 143.40 0.01667520 1.04 59 0.5163 143.40 0.01733540 1.08 60 0.5250 145.83 0.01800560 1.12 61 0.5338 148.26 0.01867580 1.16 61 0.5338 148.26 0.01933600 1.20 62 0.5425 150.69 0.02000620 1.24 63 0.5513 153.13 0.02067640 1.28 64 0.5600 155.56 0.02133660 1.32 64 0.5600 155.56 0.02200680 1.36 64 0.5600 155.56 0.02267




20 0.04 10 0.0875 24.31 0.0006740 0.08 20 0.1750 48.61 0.0013360 0.12 23 0.2013 55.90 0.0020080 0.16 24 0.2100 58.33 0.00267100 0.20 29 0.2538 70.49 0.00333120 0.24 31 0.2713 75.35 0.00400140 0.28 33 0.2888 80.21 0.00467160 0.32 36 0.3150 87.50 0.00533180 0.36 38 0.3325 92.36 0.00600200 0.40 39 0.3413 94.79 0.00667220 0.44 41 0.3588 99.65 0.00733240 0.48 43 0.3763 104.51 0.00800260 0.52 44 0.3850 106.94 0.00867280 0.56 45 0.3938 109.38 0.00933300 0.60 48 0.4200 116.67 0.01000320 0.64 49 0.4288 119.10 0.01067340 0.68 50 0.4375 121.53 0.01133360 0.72 51 0.4463 123.96 0.01200380 0.76 52 0.4550 126.39 0.01267400 0.80 53 0.4638 128.82 0.01333420 0.84 54 0.4725 131.25 0.01400440 0.88 55 0.4813 133.68 0.01467460 0.92 57 0.4988 138.54 0.01533480 0.96 59 0.5163 143.40 0.01600500 1.00 60 0.5250 145.83 0.01667520 1.04 61 0.5338 148.26 0.01733540 1.08 62 0.5425 150.69 0.01800560 1.12 63 0.5513 153.13 0.01867580 1.16 64 0.5600 155.56 0.01933600 1.20 65 0.5688 157.99 0.02000620 1.24 66 0.5775 160.42 0.02067640 1.28 67 0.5863 162.85 0.02133660 1.32 68 0.5950 165.28 0.02200680 1.36 69 0.6038 167.71 0.02267700 1.40 70 0.6125 170.14 0.02333720 1.44 71 0.6213 172.57 0.02400740 1.48 71 0.6213 172.57 0.02467760 1.52 71 0.6213 172.57 0.02533





20 0.04 10 0.0875 24.31 0.0006740 0.08 18 0.1575 43.75 0.0013360 0.12 22 0.1925 53.47 0.0020080 0.16 28 0.2450 68.06 0.00267100 0.20 31 0.2713 75.35 0.00333120 0.24 38 0.3325 92.36 0.00400140 0.28 47 0.4113 114.24 0.00467160 0.32 53 0.4638 128.82 0.00533180 0.36 58 0.5075 140.97 0.00600200 0.40 64 0.5600 155.56 0.00667220 0.44 66 0.5775 160.42 0.00733240 0.48 71 0.6213 172.57 0.00800260 0.52 75 0.6563 182.29 0.00867280 0.56 78 0.6825 189.58 0.00933300 0.60 80 0.7000 194.44 0.01000320 0.64 81 0.7088 196.88 0.01067340 0.68 85 0.7438 206.60 0.01133360 0.72 89 0.7788 216.32 0.01200380 0.76 91 0.7963 221.18 0.01267400 0.80 92 0.8050 223.61 0.01333420 0.84 93 0.8138 226.04 0.01400440 0.88 96 0.8400 233.33 0.01467460 0.92 98 0.8575 238.19 0.01533480 0.96 100 0.8750 243.06 0.01600500 1.00 106 0.9275 257.64 0.01667520 1.04 110 0.9625 267.36 0.01733540 1.08 110 0.9625 267.36 0.01800560 1.12 114 0.9975 277.08 0.01867580 1.16 115 1.0063 279.51 0.01933600 1.20 116 1.0150 281.94 0.02000620 1.24 117 1.0238 284.38 0.02067640 1.28 120 1.0500 291.67 0.02133660 1.32 121 1.0588 294.10 0.02200680 1.36 122 1.0675 296.53 0.02267700 1.40 122 1.0675 296.53 0.02333720 1.44 123 1.0763 298.96 0.02400740 1.48 124 1.0850 301.39 0.02467760 1.52 125 1.0938 303.82 0.02533780 1.56 126 1.1025 306.25 0.02600800 1.60 126 1.1025 306.25 0.02667820 1.64 127 1.1113 308.68 0.02733


840 1.68 127 1.1113 308.68 0.02800860 1.72 127 1.1113 308.68 0.02867

7.0 CALCULATION DATA ANALISYS

Strain ( 20 mm dial gauge reading) :

= Dail gauge × 0. 002Total length

= 20 x 0.00260

= 0.00067

Shear Stress (20mm dial gauge reading):

= Dail gauge × 0 . 00875Area

= 10 × 0. 008750 .06×0 . 06

= 24 .31 kN /m2

1 cm = 10 mm

1 m = 100 cm

1 m = 1000 mm

L = 60mm


60mm x 1cm x 1m

10mm x 100cm

= 0.06m

A = L x L

= 0.06m x 0.06m

= 0.0036m2

SPECIMEN NO. 1 (LOAD, F = 1.75 kg )

Use the fiveth reading with displacement 200

DISPLACEMENT

∆ L = 200 × 0.002 = 0.40 mm

LOAD

P = 45 × 0.00875

¿0.3938 kN

SHEAR STRESS

τ = P / A


i = 0.39380.0036

= 109.38 kN /m ²

STRAIN

ε L = ∆ L / L

i = 0.40mm / 60mm

= 0.00667

NORMAL STRESS

σ = P/A

= 1.75 x 9.81

0.0036 ×1000

= 4.77 kN/m

SPECIMEN NO. 2 ( LOAD, F = 2.5 kg )

Use the first reading with displacement 300

DISPLACEMENT

∆ L = 300 X 0.002 = 0.60 mm

LOAD

P = 48 × 0.00875


¿0.42 kN

SHEAR STRESS

τ = P / A

i = 0.42

0 .0036

=116.67 kN /m ²

STRAIN

ε L = ∆ L / L

i = 0.60mm / 60mm

= 0.01000

NORMAL STRESS

σ = P/A

= 2.5 x 9.81

0.0036 ×1000

= 6.81kN/m

SPECIMEN NO. 3 ( LOAD, F = 3.25 kg )

Use the third reading with displacement 400


DISPLACEMENT

∆ L = 400 X 0.002 = 0.80 mm

LOAD

P = 92× 0.00875

¿0.805 kN

SHEAR STRESS

τ = P / A

i = 0.8050.0036

= 223.61 kN /m ²

STRAIN

ε L = ∆ L / L

i = 0.80mm / 60mm

= 0.01333

NORMAL STRESS

σ = P/A

= 3.25 x 9.81

0.0036 ×1000

= 8.86 kN/m


Graf For Specimen N0.1

Graf For Specimen No.2

Graf For Specimen No.3

24.3148.61

97.22

102.08

106.94

114.24

121.53

123.96

128.82

133.68

136.11

140.97143.4

145.83

148.26

153.13

155.560

0.005

0.01

0.015

0.02

0.025

Load 1.75kg

load 1.75kg

Strain

shea

r str

engh

(kN

/m)

24.3158.33

80.2194.79

106.94119.1

126.39

133.68

145.83

153.13

160.42

167.71

172.570

0.005

0.01

0.015

0.02

0.025

0.03

Load 2.5kg

load 2.5kg2

starin

shea

r str

engt

h (k

N/m

)


8.0 DISCUSSION

A direct shear test also known as shear-box test is a laboratory or field test to measure

the shear strength properties of soil or rock material, or of discontinuities in soil or rock

24.3168.06

114.24

155.56

182.29

196.88

221.18

233.33

257.64

277.08

284.38

296.53

301.39

306.250

0.005

0.01

0.015

0.02

0.025

0.03

Load 3.25kg

load 3.25kg

strain

shea

r str

engt

h (k

N/m

)

http://en.wikipedia.org/wiki/Discontinuity

http://en.wikipedia.org/wiki/Rock_(geology)

http://en.wikipedia.org/wiki/Soil

http://en.wikipedia.org/wiki/Shear_strength


masses. Depending on the equipment, the shear test can be either stress controlled or strain

controlled. In the stress controlled tests, the shear force is applied in equal increment until

the specimen fails. The failure occurs along the plane of split of the shear box. After the

application of each incremental load, the shear displacement of the top half of the box is

measured by horizontal dial gauge. While the strain-controlled test, a constant rate of shear

displacement is applied to one-half of the box by a motor that acts through gears. The

constant rate of shear displacement is measured by a horizontal dial gauge. The test is

performed on three or four specimens from a relatively undisturbed soil sample. A specimen

is placed in a shear box which has two stacked rings to hold the sample; the contact between

the two rings is at approximately the mid-height of the sample. A confining stress is applied

vertically to the specimen, and the upper ring is pulled laterally until the sample fails, or

through a specified strain. The load applied and the strain induced is recorded at frequent

intervals to determine a stress-strain curve for the confining stress.

Direct Shear tests can be performed under several conditions. The sample is normally

saturated before the test is run, but can be run at the in-situ moisture content. The rate of

strain can be varied to create a test of undrained or drained conditions, depending whether

the strain is applied slowly enough for water in the sample to prevent pore-water pressure

buildup. Several specimens are tested at varying confining stresses to determine the shear

strength parameters, the soil cohesion (c) and the angle of internal friction

(commonly friction angle) ( ). The results of the tests on each specimen are plotted on a

graph with the peak (or residual) stress on the x-axis and the confining stress on the y-axis.

The y-intercept of the curve which fits the test results is the cohesion, and the slope of the

line or curve is the friction angle.

9.0 CONCLUSION

http://en.wikipedia.org/wiki/Friction#Angle_of_friction

http://en.wikipedia.org/wiki/Stress-strain_curve

http://en.wikipedia.org/wiki/Strain_(materials_science)


According to the graph shear stress against strain obtained from this experiment, we

found out the maximum value of shear stress were taken when the value of shear stress

remain constant. The maximum shear stress obtained from this experiment are

Specimen 1 = 155.56 kN/m2



10.0 QUESTIONS AND ANSWER

Question 1

a) Why perforated plate in this test with teeth?

The purpose that perforated plate in this test with the teeth is to grip the soil. This is to

ensure the soil does not move and slide away from the metal plate because it produces a

force applied perpendicular to the soil. It also to increase the friction of the soil with the

plate surface to avoid movement.

b) What maximum value of displacement before stop the test?

The maximum value of displacement before stop the test for load 1.75kg is 1.36 mm

while for load 2.50kg is 1.52 mm. And then, for load 3.25kg is 1.64 mm.

Question 2

c) What is the purpose of a direct shear test? Which soil properties does it measure?

This test is performed to determine the consolidated-drained shear strength of a sandy to

silty soil. The shear strength is one of the most important engineering properties of a

soil, because it is required whenever a structure is dependent on the soil’s shearing

resistance. The shear strength is needed for engineering situations such as determining


the stability of slopes or cuts, finding the bearing capacity for such as determining the

stability of slopes or cuts, finding the bearing capacity for foundations, and calculating

the pressure exerted by a soil on a retaining wall.

d) Why do we use fixing screw in this test? What will happen if you do not removed them

during test?

Function of fixing screw to place the shear box in the direct shear device and to adjust

the gap space between the shear box halves. The fixing screws used to lock the two

halves of the shear box that does not move during the experiments conducted. If do not

removed the fixing screw during test, to make failure occurs is difficult.

11.0 REFERENCE

1. Geotechnical Laboratory Labsheet ( Direct Shear Test )

2. http://en.wikipedia.org/wiki/Direct_shear_test

3. http://www.civil.mrt.ac.lk/docs/direct_shear_test.pdf

http://www.civil.mrt.ac.lk/docs/direct_shear_test.pdf

http://en.wikipedia.org/wiki/Direct_shear_test

report-direct shear test 1

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