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GEOTECHNICAL ENGINEERING CE-161P-2_1Q
CONSOLIDATED-UNDRAINED
TRI-AXIAL TEST (CU โ Test)
Problem 1: The result of undrained tri-axial test (with pore pressure measurement) on compacted soil at failure are as follows. Lateral pressure (kPa) 70 350 Total vertical pressure (kPa) 304 895 Pore Pressure (kPa) - 30 +
- Determine the angle of shearing resistance referred to the total stress.
- Determine the apparent cohesion referred to the total stress.
- Determine the angle of shearing resistance referred to the effective stress. Problem 2: A series of consolidated drained test on a normally consolidated clay indicated a friction angle of 31ยฐ. A consolidated undrained triaxial shear test on the same sample yields the following results. Confining pressure (๐ 3 ) + 200 kPa Deviators stress (โ๐) = 180 kPa
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
- Compute the undrained friction angle of the clay.
- Compute the pore pressure at the time of failure in the consolidated undrained test.
- Compute the shearing stress for the consolidated drained test. Problem 3: The shear strength of a normally consolidated clay can be given by the equation ๐ = ๐โ tan 28ยฐ. A consolidated-undrained test was conducted on the clay. Following are the results of the test. Chamber confining pressure = 105 kN/m^2 Deviator stress at failure = 97 kN/m^2
- Compute the pore water pressure developed in the clay water pressure developed in the clay specimen at failure.
- Compute the consolidated-undrained friction angle โ
.
- What would have been the deviator stress at failure if a drained test had been conducted with the same chamber confining pressure that is ๐ 3 = 105 kN/m^2. Problem 4: A sample of normally consolidated clay was subjected to a consolidated undrained tri-axial compression test that was carried out until the specimen failed at deviator stress of 50 kN/m^2. The pore water pressure at a failure was recorded to be 18 kN/m^2 and a confining pressure of 48 kN/m^2 was used in the test.
- Compute the friction angle for the total stress strength envelope.
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
- Compute the consolidated undrained friction angle for the total stress strength envelope.
- Compute the friction angle for the effective stress strength envelope.
- Compute the normal stress at the effective stress strength envelope. Problem 7: The table shows the result of consolidated undrained tri-axial tests with pore water measurements for two samples at failure. Sample Confining Total Vertical Pore Pressure (๐ 3 ) Pressure (๐ 1 ) Pressure 1 10 kPa 50 kPa - 4 kPa 2 40 kPa 100 kPa 10 kPa
- Compute the drained angle of friction.
- Compute the value of drained cohesion.
- Compute the undrained angle of friction.
- Compute the value of undrained cohesion. Problem 8: The failure stresses in a simple shear constant volume test are shown in the table below. Total normal stress on the horizontal plane = 300 kPa. Total normal stress on the vertical plane = 200 kPa. Total shear test on the horizontal and vertical planes = 100 kPa.
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
Pore water pressure = 50 kPa.
- Compute the magnitude of the max. principal effective stress.
- Compute the undrained shear strength.
- Compute the friction angle assuming the soil is nondilational. Problem 9: A consolidated undrained test (CU) was conducted on a saturated clay soil by isotropically consolidating the soil using a cell pressure of 150 kPa and then incrementally applying loads on the plunger while keeping the cell pressure constant. Failure was observed when the stress exerted by the plunger was 160 kPa and the pore water pressure recorded was 54 kPa.
- Compute the undrained shear strength of the soil.
- Compute the total stress at failure after the pore pressure was applied.
- Compute the drained angle of shearing resistance. Problem 10: Consolidated undrained tests were carried out on two samples of a clay. Each sample was isotropically consolidated before the axial stress was increased. The following results were obtained. Sample Confining Deviators Pore Pressure Stress Pressure A 420 kPa 320 kPa 205 kPa B 690 kPa 365 kPa 350 kPa
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
- Compute the pore pressure developed in the clay specimen at failure.
- If the drained test was conducted instead of an undrained test with the same chamber confining pressure of 120 kPa, what would be the major principal stress of failure. Problem 13: The results given below were obtained from a consolidated undrained tri- axial compression test on a clay soil. Cell pressure (kPa) 100 200 400 Deviator stress at failure (kPa) 248 296 388 Pore pressure at failure (kPa) 13 96 254
- Compute the drained value of shearing resistance.
- Compute the undrained angle of shearing resistance.
- Compute the undrained value of cohesion. Problem 14: The following data was recorded during a consolidated-undrained tri-axial compression test on a clay soil. Cell pressure (kPa) 100 250 400 Deviator stress at failure (kPa) 320 425 530 Pore pressure at failure (kPa) - 33.5 53 140
- Compute the undrained value of angle of shearing resistance.
- Compute the undrained value of angle cohesion.
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
- Compute the drained value of angle of shearing resistance.
- Compute the drained value of cohesion. Problem 15: The following data was recorded during an undrained tri-axial compression test on a clay soil. Cell pressure (kPa) 100 250 400 Deviator stress at failure (kPa) 262 341 420
- Compute the angle of shearing resistance.
- Compute the apparent cohesion.
- Compute the porosity of the soil at a depth of 4 m. If the shear stress at that point is 98 kPa. Sp.gr. is 2.70. Problem 16: The result of undrained tri-axial test (with the pore pressure measurement) on compacted soil at failure are as follows: Lateral pressure (kPa) 70 350 Total vertical pressure (kPa) 304 895 Pore pressure (kPa) - 30 +
- Determine the angle of shearing resistance referred to the total stress.
- Determine the apparent cohesion referred to the total stress.
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
Sample Confining Total Vertical Pore Pressure Pressure Pressure (๐ 3 ) (๐ 1 ) (uf) 1 220 480 78 2 420 760 216
- Compute the friction angle.
- Compute the cohesion of clay sample.
- Is the clay normally consolidated or over consolidated? Problem 18: Pore pressure measurements were made during undrained tri-axial tests on samples of compacted fill material from an earth dam after saturating them in the laboratory. The results were as follows: Property measured (T/m 2 ) Test 1 Test 2 Lateral pressure (๐ 3 ) 15 45 Total vertical pressure (๐ 1 ) 40 100 Pore water pressure (u) 3 12.
- Compute the apparent angle of shearing resistance as referred to the total stress.
- Compute the apparent cohesion as referred to the total stress.
- Compute the apparent angle of shearing resistance as referred to the effective stress.
- Compute the apparent cohesion as referred to the effective stress.
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
Problem 19: A soil sample of saturated sand was consolidated under an all around pressure of 420 kPa. The axial stress was then increased and drainage was prevented. The soil sample failed when the axial deviator stress reached 350 kPa. Pore water pressure at failure was 290 kPa.
- Compute the consolidated-undrained angle of shearing resistance.
- Compute the drained angle of friction.
- Compute the major principal effective stress at failure. Problem 20: A consolidated-undrained test on a normally consolidated clay yield the following results. Confining pressure ๐ 3 = 150 kPa Deviator stress โ๐๐ = 130 kPa Pore pressure โ๐ข๐ = 80 kPa
- Calculate the consolidated undrained friction angle.
- Calculate the consolidated drained friction angle.
- Calculate the normal stress at the failure plane at drained condition. Problem 21:
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
consolidated-undrained conditions. At failure, the respective minor and major principal stress values are 20 kPa and 46 kPa for sample one and 40 kPa and 80 kPa for sample two.
- Compute the value of the angle of friction.
- Compute the cohesion of the soil sample.
- What shear strength is expected on a plane where the normal stress is 70 kPa. Problem 24: A normally consolidated clay sample is subject to tri axial test where pore eater pressure measurements are made. A consolidated-undrained type of test is performed. The sample fails (shear) when the total all-around confining pressure is 45 kPa and the total axial pressure is 97 kPa. At failure, the recorded pore water pressure is 20 kPa.
- Determine the undrained angle of friction for the total stress strength envelope.
- Determine the drained angle of friction for the effective stress strength envelope.
- Determine the normal stress at the point of the failure plane at drained condition. Problem 25: The following results were obtained from undrained tri-axial compression tests on three identical specimens of saturated soil. Lateral pressure (kN/m^2 ) 70 140 210 Total vertical stress (kN/m^2 ) 217 287 357
GEOTECHNICAL ENGINEERING CE-161P-2_1Q
Inclination of plane of rupture to cross section of specimen: 51 ยฐ 53 ยฐ 52 ยฐ
- Compute the undrained cohesion of soil.
- Compute the undrained shearing resistance.
- Compute the angle of internal friction.
