Method for determination of shear strength of soil (Badarpur Sand) with a maximum particle size of 4.75 mm in drained conditions using Direct Shear Test apparatus.
It is a Floating Box type test in which upper half box is floating due to application of vertical loading resulting in lateral confinement thus generating sufficient friction which holds the upper half of shear box.
In the shear box test, the specimen is not failing along its weakest plane but along a predetermined or induced failure plane i.e. horizontal plane separating the two halves of the shear box. This is the main drawback of this test.
Moreover, during loading, the state of stress cannot be evaluated. It can be evaluated only at failure condition. Also, failure is progressive.
Booking open Available Pune Call Girls Pargaon 6297143586 Call Hot Indian Gi...
Direct Shear Test
1. 1
Department of Civil Engineering, IIT Delhi
Submitted By:
Abhinav Kumar
Disclaimer: This presentation is for educational purposes only. Opinions or points of
view expressed in this presentation represent the view of the presenter, and does not
necessarily represent the official position or policies of IIT Delhi. Nothing in this
presentation constitutes legal advice. The individuals appearing in this presentation, if
any, are depicted for illustrative purposes only and are presumed innocent until
proven guilty in a court of law. Under no circumstance shall we have any liability to
you for any loss or damage of any kind incurred as a result of the use of the data or
reliance on any information provided. Your use of the document and your reliance on
any information is solely at your own risk
Soil Engineering Lab
REPORT TITLE (06)
Direct Shear Test
2. 2
Objective: Method for determination of shear strength of soil (Badarpur Sand) with a maximum
particle size of 4.75 mm in drained conditions using Direct Shear Test apparatus.
Apparatus:
1. Direct Shear Test Apparatus-
Loading Frame, Weights, Proving Ring, Micrometer Dial Gauge, Sample Trimmer or Core Cutter,
Stop Watch, Balance, Spatula, Straight Edge, Shear box grid plates, porous stones, base plates,
loading pad and water jacket shall conform to IS: 11229-1985.
(a) Upper and lower parts
of shear box coupled
together with two pins.
(b) Grid plates - 2 pairs
(c) Stone plates
(d) 4 Base plate
(e) Top plate
(f) Loading pad, and the
balance of 1 kg capacity,
sensitive to 0.1 g.
2. Weights - for providing the
required normal loads.
Testing methods and Procedures:
1. Specimen Preparation (Remoulded)
Cohesionless soil (Badarpur Sand) with relative density 70% was tamped
in the shear box itself with the base plate and grid plate or porous stone
as required in place at the bottom of the box.
2. Undisturbed Specimen -Specimens of required size shall be prepared
from the undisturbed specimen collected from field in accordance with
IS: 2720 (Part 1)-1983.
3. Consolidated Drained Test-The shear box with sample and perforated
grid plates and porous stones was fitted into the load frame. After
application of normal stress which is done in increments [ IS: 2720 (Part
15)-1986, the sample was allowed to consolidate. When the consolidation
has completely occurred, the shear test should be done at such a slow
rate that at least 95 percent pore pressure dissipation occurs during the
test in this calculated time factor. At the end of the test, the specimen
should be removed from the box and the final moisture content
measured. A minimum of three (preferably four) tests were made on
separate specimens of the same density at different normal stresses.
Shear Box Assembly
3. 3
4. Strain controlled direct shear machine consists of shear box, soil container, loading unit, proving ring,
dial gauge to measure shear deformation and vertical deformation. A proving ring is used to indicate the
shear load taken by the soil along the shearing plane.
Calculations:
1. From the calibration chart of the proving-ring, the loads corresponding to the load dial readings
obtained during the test was calculated. The loads so obtained divided by the corrected cross-sectional
area of the specimen gives the shear stress in the sample. The corrected cross-sectional area shall be
calculated from the following equation:
Corrected Area (Ac) = Ao(1 - (δ/3))
where,
Ao = initial area of the specimen in cm2
and
δ = displacement in cm.
2. The longitudinal displacement at a particular load was either noted directly from the strain dial
readings or calculated as the product of the corresponding time reading and the strain rate, allowing for
the compression of the proving-ring, where applicable. The stress longitudinal displacement readings
were plotted and the maximum stress and corresponding longitudinal displacement together with the
normal load applied during the test recorded.
3. The maximum shear stress and the corresponding longitudinal displacement and applied normal stress
were recorded for each test and the results were presented in the form of a graph in which the applied
normal stress is plotted as abscissa and the maximum shearing stress is plotted as ordinate to the same
scale. The angle which the resulting straight line makes with the horizontal axis and the intercept which
the straight line makes with the vertical axis shall be reported as the angle of shearing resistance and
cohesion intercept respectively.
4. i. Shear Stress = (Proving ring reading x Proving ring constant)/Acorrected
ii. Horizontal displacement = (Horizontal dial gauge reading) x (Least count of horizontal dial gauge)
iii. Vertical displacement = (Vertical dial gauge reading) x (Least count of vertical dial gauge)
5. Shear stress at failure needs to be calculated for all three tests performed at three different normal
stresses to plot the failure envelope.
4. 4
Load
(kN)
Comp.
Division
0 0
0.3 141
0.6 282
0.9 425
1.2 567
1.5 712
1.8 856
2.1 1002
2.4 1145
2.7 1291
3 1438
Direct Shear Test Assembly
0
200
400
600
800
1000
1200
1400
1600
0 1 2 3 4
Comp.
Division
Load (kN)
Calibration for Proving Ring No- 15927
Proving Ring
Loading Yoke
Counter Weight
Vertical Dial Gauge
Lever Arm
Holding Screw
Horizontal Dial Gauge
Frame
Motor
11. 11
Normal stress (kPa) Shear stress (kPa)
50 53.538
100 91.51
150 146.20
Cohesion (C) 4.42 kPa
Angle of Shearing Resistance (Ø) 42.82°
y = 0.9266x + 4.4213
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
0 20 40 60 80 100 120 140 160
Shear
Stress
(kPa)
Normal Stress (kPa)
Shear stress vs Normal stress
12. 12
Individual Discussion:
1. The loading cap tilted downwards (as shown in fig) on the
motor side (opposite to proving ring) from where horizontal
displacement was applied, due to removal of the sand sample
from the gap created due to shearing of upper half and lower
half shear box.
2. It is a Floating Box type test in which upper half box is floating
due to application of vertical loading resulting in lateral
confinement thus generating sufficient friction which holds the
upper half of shear box.
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Vertical
Displ.
(mm)
Horizontal Displ. (mm)
Vertical Vs Horizontal Displ. Curve
50 kPa 100 kPa 150 kPa
Tilting of Loading Cap
13. 13
3. In the shear box test, the specimen is not failing along its weakest plane but along a
predetermined or induced failure plane i.e. horizontal plane separating the two halves of the
shear box. This is the main drawback of this test.
Moreover, during loading, the state of stress cannot be evaluated. It can be evaluated only at
failure condition. Also, failure is progressive.
4. The angle of shearing resistance of sands depends on state of compaction, coarseness of grains,
particle shape and roughness of grain surface and grading. It varies between 28° (uniformly
graded sands with round grains in very loose state) to 46° (well graded sand with angular grains in
dense state).
5.
Soil Type Angle of Shearing Resistance
(Ø)
Cohesion (C)
Badarpur Sand 42.82° 4.42 kPa
Yamuna Sand 31.70° 18.9 kPa
6. Direct shear test is simple and faster to operate. As thinner specimens are used in shear box, they
facilitate drainage of pore water from a saturated sample in less time. This test is also useful to
study friction between two materials – one material in lower half of box and another material in
the upper half of box.
7. In general, loose sands expand and dense sands contract in volume on shearing. There is a void
ratio at which either expansion contraction in volume takes place. This void ratio is called critical
void ratio. Expansion or contraction can be inferred from the movement of vertical dial gauge
during shearing.
References:
1. IS: 2720 (Part 13):1986 Methods of test for soils: Direct shear test. Reaffirmed- 2016.
2. IS: 11229-1985.
3. IS: 2720 (Part 15)-1986
4. ASTM D 3080 - 04