A sand sample is subjected to direct shear testing at its normal (in situ) water content. Two tests are performed. For one of the tests, the sample shears at a stress of 3,000 psf when the normal...

A sand sample is subjected to direct shear testing at its normal (in situ) water content. Two tests are performed. For one of the tests, the sample shears at a stress of 3,000 psf when the normal stress is 4,000 psf. In the second test, the sample shears at a stress of 4,000 psf when the normal stress is 6,000 psf. From these data, determine the value of apparent cohesion and the corresponding angle of internal friction.