A consolidated undrained test was conducted on a specimen of an OC clay, During

Question

A consolidated undrained test was conducted on a specimen of an OC clay, During the consolidation stage, the specimen was backpressurized to ensure saturation. In order to do that, backpressures of 10 kPa, 20 kPa, and 30 kPa and were applied and the corresponding the increases in total stresses during the consolidation were 8 kPa, 18 kPa, and 29 5 kPa. After the consolidation stage, loading was started and the pore water pressure up to 225 kPa and the cell pressure was 725 kPa, The specimen was loaded with an induced of 600 kPa during shear. The friction angle of the sand is 38 degree. Was the specimen completely saturated before shear? Why? Determine the minor and major principal effective stresses at failure. Will the volume, water content and void ratio of the specimen change as a result of shearing? Will the specimen swell or compress during shear? Explain briefly,

Explanation / Answer

skempton pore pressure parameter

B= change change in otal stress/change in back pressure = 29.5/30=0.9833

although for fully saturation B should be 1 bet B is very close to one (0.9833) hence we can say sample is fully saturated.

b)

given 1 - 3 = 600

3 = 725 kpa

1 = 1325 kpa

'1 = 1 - u = 1325-225= 1100 KPa

'3 = 3 - u = 725 -225= 500 KPa

c)

no none of these parameter will change because its undrained test and there is no expelsion of pore water pressure.

thanks

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