Student Name: Andrea Bartholomew
Student ID: 83734
Programme: BAsc. In Civil Engineering
Cohert: Full Time
Course Code: GOET2009
Course Name: Geotechnics II
Instructor: Saeed Mohomed
Assignment: Direct Shear Test Lab
Due Date: 18th April 2021
Table of Contents
Purpose:...................................................................................................................................... 3
Conclusion: ................................................................................................................................ 3
Theory: ....................................................................................................................................... 3
Apparatus: .................................................................................................................................. 5
Procedure: .................................................................................................................................. 5
Data and Sample Calculations ................................................................................................... 6
Results ........................................................................................................................................ 7
Discussion of Results ................................................................................................................. 8
Appendices ................................................................................................................................. 9
Bibliography ............................................................................................................................ 11
Participation ............................................................................................................................. 12
Purpose:
This test is used to assess a sandy to silty soil's consolidated-drained shear strength. Since shear
strength is necessary whenever a structure is dependent on the soil's shearing resistance, it is
one of the most important engineering properties of a soil. Shear strength is needed in
engineering circumstances such as determining the stability of slopes or cuts, determining
foundation bearing power, and measuring the pressure exerted by soil on a retaining wall.
Conclusion:
In conclusion, the aim of a direct shear test is to determine the soil's shear strength by forcing
it to shear at a constant rate along the induced horizontal plane of weakness. Shear strength is
needed in engineering circumstances such as determining the stability of slopes or cuts,
determining foundation bearing power, and measuring the pressure exerted by soil on a
retaining wall. The direct shear test has many advantages over other shear tests, including ease
of setup and equipment, as well as the ability to test under various saturation, drainage, and
consolidation conditions. The shear strength of soil is 2.149 kg/cm2 based on the direct shear
or shear box apparatus experiment. As a result, the target has been met.
Theory:
Shear strength of a soil is the maximum resistance to shearing stress at failure on the failure
plane.
Shear strength is composed of:
1. Internal friction which is the resistance due to friction between individual particles at
their contact points and interlocking of particles. This interlocking strength is indicated
through parameter, φ.
2. Cohesion which resistance due to inter-particle force which tend hold the particles
together in a soil mass. The indicative parameter is called Cohesion intercept ( c ).
Coulomb has represented the shear strength of soil by the equation:
τf = c + δn tan φ
Where,
τf = shear strength of soil = shear stress at failure.
c = cohesion intercepts.
δn = total normal stress on the failure plane
φ = Angle of internal friction or shearing resistance
the graphical representation of the above equation gives a straight line called Failure envelope.
The parameters c and are not constant for a given type of soil but depends in its degree of
saturation, drainage conditions and the conditions of laboratory testing.
In direct shear test, the sample is sheared along the horizontal plane. This indicates that the
failure plane is horizontal. The normal stress, on the plane is the external vertical load divided
by the corrected area of the soil sample. The shear stress at failure is the external lateral loads
divided by the corrected of soil sample.
Apparatus:
(Special) shear test frame housing dimension 60 mm x 60 mm x 25 mm, water jacket for shear
box, metallic grid plates, base plate, porous stones, loading pad, roving ring of capacity 200
Kgf, slotted weights to impart appropriate normal stress on soil sample.
(General) balance of capacity 1 kg and sensitivity 0.1 gms, scale, dial guage off sensitivity
0.01mm
Procedure:
1. A soil specimen of size 60 mm x 60 mm x 25 mm was prepared from either an
undisturbed soil sample or compacted/remoulded soil sample. Soil specimen may also
be directly prepared in the box by compaction.
2. The upper part of the box to the lower box was fixed by fixing screws. The base plate
was attached to the lower part.
3. The porous stone was placed in the box.
4. The soil specimen prepared was transferred into the box.
5. The upper grid, porous stone and loading pad was placed in the order on soil specimen.
6. The upper half of the box was brought in contact with providing ring assembly. Contact
is observed by the slight movement of proving ring dial gauge needle.
7. The loading yoke was mounted on the ball placed on the loading pad
8. The weight was placed on the loading yoke to apply a given value of normal stress
intensity. The weight of the yoke was added also in the estimation of normal stress
intensity.
9. The fixing screws was removed from the box and the upper box was raised slightly with
the help of the spacing screws. The spacing screws were removed.
10. The entire dial was adjusted to read at zero.
11. Shear load is applied at constant rate of strain.
12. The readings of proving ring and dial readings at a fixed interval was recorded.
13. The observation was continued till the specimen fails.
14. The test was repeated on the identical specimen under increasing normal stress and the
corresponding reading was recorded.
Data and Sample Calculations
1. Size of Soil sample = Internal Dimensions of the Box
2. Weight of yoke, w1=0.775 Kg.
3. Weight of Loading pad, w2=0.620 Kg.
4. Lever Ratio = 1:5
5. Proving ring Number=
6. Proving ring Constant (K): 1 Division = Kg.
7. Rate of strain for Horizontal Shear = 1.25 mm/min.
Table 1:
Load on yoke (w) (kg)
Normal load on soil sample(N)
(kg)=(W+w1)x5+w2
Normal stress (kg/cm2 ) = N/(6x6)
Proving ring division at failure (D)
Shear force at failure (S) =D x k
Shear resistance at failure (
‫ד‬f ) =S/(6x6)
Results
Table 5:
Normal Stress (kg/cm3)
Shear Stress (kg/cm3)
0.5
0.692
1
0.436
1.5
0.376
2
1.353
Graph 1:
Shear Stress VS. Horizontal Deformation
1,6
Shear Stress, kg/cm3
1,4
1,2
1
0,8
0.5
0,6
1
0,4
1.5
0,2
0
0
2
4
6
8
Horizontal Displacement, mm
Graph 2:
10
12
Shear Stress Vs. Normal Stress
1,6
Shear Stress (kg/cm3)
1,4
1,2
1
0,8
0,6
0,4
0,2
0
0
0,5
1
1,5
2
2,5
Normal Stress (kg/cm3)
Discussion of Results
From the Graph 2, shear stress vs normal stress, the shear strength of the soil was obtained
using coulombs equations with the cohesion ( c ) = 0.23 kg/cm2, Internal friction angle, = 21 ̊
Using Coulomb’s equation; τf = c + σ tan φ = 0.23 + 5 tan 21. Hence, the shear strength,τf =
2.149 kg/cm2. The sample is consolidated using four different weights and then sheared at the
same constant rate in four subtests. Then, for each set of tests, plot the graph between shear
stress and horizontal displacement. Chart the second graph between each test's normal stress
and maximum shear stress. The standard stress and shear stress graph can be used to calculate
the soil's cohesion and friction angle. Direct shear stress has a number of advantages, including
direct measurement of shear strength, quick and fast sample preparation, and the ability to test
almost any soil form. Shear strength is only evaluated on a predefined shear plane, stress
distribution along the shear plane is not standardized, and only total stresses are applied, even
when measuring dry granular material since pore water pressures cannot be measured.
Appendices
Table 2: Normal Stress = 0.5kg/cm2
Horizontal
Guage Reading
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
Proving
Ring
Reading
0
16
21
26
29
33
35
37
38
39
40
40
41
41
41
42
46
46
46
46
45
Horizontal/Shear
Deformation
(mm)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
Shear
Force
(kg)
0
6.8
8.925
11.05
12.325
14.025
14.875
15.725
16.15
1.575
17
17
17.425
17.425
17.425
17.85
19.55
19.55
19.55
19.55
19.125
Table 3: Normal Stress = 1.0kg/cm2
Horizontal Proving Horizontal/Shear
Guage
Ring
Deformation
Reading Reading
(mm)
0
0
0
50
13
0.5
100
17
1
150
20
1.5
200
23
2
250
24
2.5
Shear
Force
(kg)
0
5.525
7.225
8.5
9.775
10.2
Shear
Stress(kg/cm3
0
0.195
0.256
0.301
0.346
0.361
Shear
Stress(kg/cm3
0
0.241
0.316
0.391
0.436
0.496
0.526
0.556
0.571
0.586
0.601
0.601
0.616
0.616
0.616
0.631
0.692
0.692
0.692
0.692
0.677
300
350
400
450
500
550
600
650
700
26
27
27
28
28
29
29
29
29
3
3.5
4
4.5
5
5.5
6
6.5
7
11.05
11.475
11.475
11.9
11.9
12.325
12.325
12.325
12.325
0.391
0.406
0.406
0.421
0.421
0.436
0.436
0.436
0.436
Table 4: Normal Stress = 1.5kg/cm2
Horizontal Proving Horizontal/Shear Shear
Shear
Guage
Ring
Deformation
Force Stress(kg/cm3
Reading Reading
(mm)
(kg)
0
0
0
0
0
50
16
0.5
6.8
0.241
100
21
1
8.925
0.316
150
52
1.5
22.1
0.782
200
61
2
25.925
0.917
250
69
2.5
29.325
1.037
300
74
3
31.45
1.112
350
79
3.5
33.575
1.188
400
83
4
35.275
1.248
450
87
4.5
36.975
1.308
500
89
5
37.825
1.338
550
90
5.5
38.25
1.353
600
90
6
38.25
1.353
650
89
6.5
37.825
1.338
700
87
7
36.975
1.308
750
86
7.5
36.55
1.293
800
84
8
35.7
1.263
850
83
8.5
35.275
1.248
900
82
9
34.85
1.233
950
81
9.5
34.425
1.218
Bibliography
1. URL: https://scetcivil.weebly.com/uploads/5/3/9/5/5395830/experiment_12direct_shear.pdf
2. URL: http://smfe-iiith.vlabs.ac.in/exp9/Exp-9%20DirectshearTest.pdf
Participation
Andrea Bartholomew: Results
Khelsy Munroe: Results