1) A sample of clay has been taken from 7 m below the bed of a...

  

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1) A sample of clay has been taken from 7 m below the bed of a river. It is known that the unit weight of the clay Y = 20.5 kN/m³ and that the over consolidation ratio is 2.5. Determine how much soil has been removed by erosion (NB. Assume the weight of the soil removed was also 20.5 kN/m³). 2) A layer of clay 8 m thick is to be surcharged during the construction of an embankment. The clay overlays a highly permeable sand. Laboratory tests have provided the following properties for the clay: cv 10 mm²/minute and Uz = 1.13T05 Estimate the time required for the clay to reach 60 % consolidation. 3) A uniform layer of sand 8m thick overlies a homogeneous saturated clay layer 4 m thick. The clay has a very low permeability. The water table is 4 m below the top of the sand layer. It can be assumed that the soil layers and the water table are horizontal. The sand and the clay have the following properties: SAND: Saturated unit weight Unit weight above water table = 21.64 kN/m3 = 20.71 kN/m3 CLAY: Saturated unit weight = 20 kN/m3 i) Determine the total and effective vertical stress at the centre of the clay layer. ii) If, in the above strata, the water table was permanently at the upper surface of the sand layer, what would be the total and effective vertical stresses at the centre of the clay? iii) Also taking the water table to be at the upper surface of the sand, determine the total and effective vertical stresses at the centre of the clay layer immediately after an extensive 4 m thick overlay of fill (of unit weight 20kN/m³) is placed rapidly on top of the sand. What will the effective stress at the centre of the clay be after several years application of the extensive fill layer? Explain your reasoning. 4) Provide an explanation of the main types of triaxial test that can be performed. Comment on how these tests may relate to differing field conditions. 5) 6) A sample of dry, cohesionless soil was subject to a triaxial compression test that was carried out until the specimen failed at a deviator stress of 105.4 kN/m². A confining pressure (a,) of 48 kN/m² was used for the test. Estimate the angle of internal friction of the soil. a) A specimen of dry sand was subject to a direct shear test (shear box) that was carried out until the specimen sheared. A normal stress of 96 kN/m² was imposed for the test and the shear stress at failure was found to be 65 kN/m². Estimate the angle of friction of the sand. b) A series of direct shear tests were performed on a soil sample. Each test was carried out until the soil specimen experienced shear failure. The test data are given in Table 1. Determine the cohesion and angle of internal friction (with respect to total stress). Specimen No. Normal Stress (kN/m²) Shear Stress at Failure (kN/m²) 1 29 73 2 44 77 3 60 83 7) In the analysis of 1D consolidation the following equality is often used: ΔΗ AV Ae H V 1+e 8) Explain the basis of this statement and show how volumetric strain can be stated in terms of void ratio in this manner (Hint: use a unit volume of solid phase model to assist with your answer). It is known that soil properties may vary with depth. Explain how you would estimate primary settlement of a layered soil profile where M is known to vary with each layer of soil. 1) A sample of clay has been taken from 7 m below the bed of a river. It is known that the unit weight of the clay Y = 20.5 kN/m³ and that the over consolidation ratio is 2.5. Determine how much soil has been removed by erosion (NB. Assume the weight of the soil removed was also 20.5 kN/m³). 2) A layer of clay 8 m thick is to be surcharged during the construction of an embankment. The clay overlays a highly permeable sand. Laboratory tests have provided the following properties for the clay: cv 10 mm²/minute and Uz = 1.13T05 Estimate the time required for the clay to reach 60 % consolidation. 3) A uniform layer of sand 8m thick overlies a homogeneous saturated clay layer 4 m thick. The clay has a very low permeability. The water table is 4 m below the top of the sand layer. It can be assumed that the soil layers and the water table are horizontal. The sand and the clay have the following properties: SAND: Saturated unit weight Unit weight above water table = 21.64 kN/m3 = 20.71 kN/m3 CLAY: Saturated unit weight = 20 kN/m3 i) Determine the total and effective vertical stress at the centre of the clay layer. ii) If, in the above strata, the water table was permanently at the upper surface of the sand layer, what would be the total and effective vertical stresses at the centre of the clay? iii) Also taking the water table to be at the upper surface of the sand, determine the total and effective vertical stresses at the centre of the clay layer immediately after an extensive 4 m thick overlay of fill (of unit weight 20kN/m³) is placed rapidly on top of the sand. What will the effective stress at the centre of the clay be after several years application of the extensive fill layer? Explain your reasoning. 4) Provide an explanation of the main types of triaxial test that can be performed. Comment on how these tests may relate to differing field conditions. 5) 6) A sample of dry, cohesionless soil was subject to a triaxial compression test that was carried out until the specimen failed at a deviator stress of 105.4 kN/m². A confining pressure (a,) of 48 kN/m² was used for the test. Estimate the angle of internal friction of the soil. a) A specimen of dry sand was subject to a direct shear test (shear box) that was carried out until the specimen sheared. A normal stress of 96 kN/m² was imposed for the test and the shear stress at failure was found to be 65 kN/m². Estimate the angle of friction of the sand. b) A series of direct shear tests were performed on a soil sample. Each test was carried out until the soil specimen experienced shear failure. The test data are given in Table 1. Determine the cohesion and angle of internal friction (with respect to total stress). Specimen No. Normal Stress (kN/m²) Shear Stress at Failure (kN/m²) 1 29 73 2 44 77 3 60 83 7) In the analysis of 1D consolidation the following equality is often used: ΔΗ AV Ae H V 1+e 8) Explain the basis of this statement and show how volumetric strain can be stated in terms of void ratio in this manner (Hint: use a unit volume of solid phase model to assist with your answer). It is known that soil properties may vary with depth. Explain how you would estimate primary settlement of a layered soil profile where M is known to vary with each layer of soil.

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