Two drained triaxial compression tests are carried out on "identical" specimens of clean sand. In each test, a fully saturated specimen is consolidated to a confining stress and then failed by increasing the vertical stress. The test results are summarized in the following table. Assume the specimens in these two tests are uniform and have the same density. Cell pressure Deviatoric stress q (kPa) σ3 (kPa) Test No. Test 1 (Drained) Test 2 (Drained) Test 2a (Undrained) 100 200 200 Peak stress state 270.0 540.0 150.0 Residual state (or critical state) 200.0 400.0 70.0 (a) Using the results of Tests 1 and 2, determine the effective friction angle of the sand at peak failure state. (b) What is most likely the orientation of the shear failure plane in Test 1? (c) When repeating Test 2, the technician did not open the drainage valve by mistake when shearing the specimen after consolidation. In other words, the consolidated specimen was sheared under the undrained condition. The maximum deviatoric stresses were measured as 150 kPa with the deviatoric stress of 70 kPa at the residual state. Explain why the test results in Test 2 and Test 2a are different.

Two drained triaxial compression tests are carried out on "identical" specimens of clean sand. In each test, a fully saturated specimen is consolidated to a confining stress and then failed by increasing the vertical stress. The test results are summarized in the following table. Assume the specimens in these two tests are uniform and have the same density. Cell pressure Deviatoric stress q (kPa) σ3 (kPa) Test No. Test 1 (Drained) Test 2 (Drained) Test 2a (Undrained) 100 200 200 Peak stress state 270.0 540.0 150.0 Residual state (or critical state) 200.0 400.0 70.0 (a) Using the results of Tests 1 and 2, determine the effective friction angle of the sand at peak failure state. (b) What is most likely the orientation of the shear failure plane in Test 1? (c) When repeating Test 2, the technician did not open the drainage valve by mistake when shearing the specimen after consolidation. In other words, the consolidated specimen was sheared under the undrained condition. The maximum deviatoric stresses were measured as 150 kPa with the deviatoric stress of 70 kPa at the residual state. Explain why the test results in Test 2 and Test 2a are different.

Structural Analysis

6th Edition

ISBN:9781337630931

Author:KASSIMALI, Aslam.

Publisher:KASSIMALI, Aslam.

Chapter2: Loads On Structures

Section: Chapter Questions

Problem 1P

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Concept explainers

Test for Determination of Shear Strength

The term shear strength is often associated with the soil. Shear strength is defined as the resistance to the deformation of soil particles due to the continuous action of shear stress. In short, shear strength is the maximum shear stress that a soil can sustain.

Question

Two drained triaxial compression tests are carried out on "identical" specimens of clean
sand. In each test, a fully saturated specimen is consolidated to a confining stress and then
failed by increasing the vertical stress. The test results are summarized in the following
table. Assume the specimens in these two tests are uniform and have the same density.
Cell pressure
Deviatoric stress q (kPa)
σ3 (kPa)
Test No.
Test 1 (Drained)
Test 2 (Drained)
Test 2a (Undrained)
100
200
200
Peak stress state
270.0
540.0
150.0
Residual state
(or critical state)
200.0
400.0
70.0
(a) Using the results of Tests 1 and 2, determine the effective friction angle of the sand at
peak failure state.
(b) What is most likely the orientation of the shear failure plane in Test 1?
(c) When repeating Test 2, the technician did not open the drainage valve by mistake when
shearing the specimen after consolidation. In other words, the consolidated specimen
was sheared under the undrained condition. The maximum deviatoric stresses were
measured as 150 kPa with the deviatoric stress of 70 kPa at the residual state. Explain
why the test results in Test 2 and Test 2a are different.

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A direct shear test is conducted on a 60 mm X 60 mm overconsolidatedclay specimen. The loading was very slow,ensuring that there is no pore water pressure developmentwithin the specimen (i.e., drained loading). The followingdata were recorded.
# 3) A sand soll sample is subjected to a direct shear test under a normal load of 185 kPa. The specimen failed when the shear stress reached 100 kPa. If the normal load is increased to 240 kPa, what will be the shear strength of the specimen?
A certain saturated sand (S = 100%) has a moisture content of 27.9% and a specific gravity of solids of 2.61. It also has a maximum index void ratio of 0.90 and a minimum index void ratio of 0.33. Compute its relative density and classify its consistency. (Table on the right) Solution: Given the values of mmoisture content, specific gravity and degree of saturation, the void ratio can be estiamted as: e = Thus the relative density is found to be Dr = • According to the table, the soil is classified as %; soil. TABLE 3.3 CONSISTENCY OF COARSE-GRAINED SOILS AT VARIOUS RELATIVE DENSITIES (data from Lambe and Whitman, 1969) Relative Density, D,(%) 0-15 15-35 35-65 65-85 85-100 Classification Very loose Loose Medium denseª Dense Very dense "Lambe and Whitman used the term "medium," but "medium dense" is better because "medium" usually refers to the particle size distribution.
a) A CU triaxial test was carried out on a silty sand soil sample. The cell pressure was equal to 200 kPa. At failure the deviator stress was equal to 410 kPa and the pore pressure was equal to 73 kPa. i) Assuming that the cohesion intercept is equal to 0, calculate the friction angle of the soil. ii) If the friction angle was equal to 35°, calculate the cohesion intercept of the soil. iii) Calculate the angle of the failure plane relative to the horizontal plane for the soil shear strength parameters in Question 4 a i and 4 a ii.
Note) For soil sample in Table 2, initial thickness of sample = 14.31 mm, sample area = 2827.433 mm^2, dry weight measured at the end of test = 52.53 g, specific gravity = 2.7 Also, Determine the compression index and expansion index Please show graph