Problem 3) Two boring samples of the same sand were retrieved from two different layers of...

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Problem 3) Two boring samples of the same sand were retrieved from two different layers of soil (both were above the known ground water level). A lab technician performs a CD triaxial test on both specimens to gather results. (a) Explain why a CD test is appropriate in this scenario. (b) For the first sample, a confining pressure was set to be 20 psi during the consolidation phase. At failure, she records the total vertical stress to be 52 psi as shown in Figure 1. What is the angle of friction of the sand? What is the angle of failure, Ocr? (c) A second sample retrieved from a greater depth below the soil was tested and failed at a deviator stress of 62 psi. What are the shear stress and effective normal stress on the failure plane? 52 psi 20 psi Figure 1: Stresses on soil sample during failure for part (b). Problem 3) Two boring samples of the same sand were retrieved from two different layers of soil (both were above the known ground water level). A lab technician performs a CD triaxial test on both specimens to gather results. (a) Explain why a CD test is appropriate in this scenario. (b) For the first sample, a confining pressure was set to be 20 psi during the consolidation phase. At failure, she records the total vertical stress to be 52 psi as shown in Figure 1. What is the angle of friction of the sand? What is the angle of failure, Ocr? (c) A second sample retrieved from a greater depth below the soil was tested and failed at a deviator stress of 62 psi. What are the shear stress and effective normal stress on the failure plane? 52 psi 20 psi Figure 1: Stresses on soil sample during failure for part (b).

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