(a) A dry sand sample is tested in direct shear. The test procedure includes having a normal (compressive) stress of 200 kPa imposed while the sample undergoes shearing. The sample fails when the...

(a) A dry sand sample is tested in direct shear. The test procedure includes having a normal (compressive) stress of 200 kPa imposed while the sample undergoes shearing. The sample fails when the shear stress reaches 135 kPa. From this data, determine the angle of internal friction f for the soil.

(b) A second sample of the same sand is also to be tested in direct shear, but the applied normal (compressive) stress will be 145 kPa. What shear stress is expected to cause the sample to fail?