Section 4. Stability issues related to the embankment construction As the alluvial clay is soft, the...

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Section 4. Stability issues related to the embankment construction As the alluvial clay is soft, the placement of a 3-m sand embankment may cause some stability issues (Figure 5). To estimate the stability of the sand embankment, samples of sand (Sample 1) and the alluvial clay (Sample 2) were collected for testing. You are required to estimate the strength characteristics of these soils. Note that these strength parameters (cohesion and friction angle) are necessary for slope stability analysis. Alluvium Embankment Sample 1 Sample 2 Failure plane Sandstone Figure 5. Potential failure plane in the alluvial clay due to the placement of the fill Sample 1-Embankment sand Table 7: Data from a series of shear box tests on Sample 1. Material: Sand Sample area: 20 cm² Normal Force, IN 0.18 0.33 0.79 1.18 Test N. 1 3 Shear force at failure, kN 0.09 0.16 0.41 Embankment 0.58 Tasks to complete: 4a. Plot the shear box test results obtained for the sand samples (Table 7) and determine the shear strength parameters of this soil. Using the obtained shear strength parameters, estimate the factor of safety for the slope, which is schematically shown in Figure below. Use the following data: Failure plane Conditions: at the end of embankment construction (water seepage parallel to the slope) h-2m B-38° Data on density and water content of the embankment sand is given in the beginning of Section 3 4b. Use the shear strength parameters from Q4a. A and B parameters of this saturated sand are 0.85 and 0.97 respectively. A triaxial sample of this soil is consolidated under a cell pressure of 200 kN/m² and back pressure (pore water pressure) of 100 kN/m². Once the consolidation was completed, the sample was sheared under undrained conditions by applying a vertical load. What would be the principal stress difference and pore water pressure at failure? Provide your working out below; add more pages if necessary Sample 2-Alluvial silty clay A series of consolidated drained triaxial tests were performed on the alluvial clay specimens and the obtained results are summarized in Table 8.1 Table 8: Results of triaxial tests on Sample 2. Test N. Confining Pressure, kN/m² 50 100 200 2 3 Deviator stress at failure q, kN/m² 129 163 Tasks to complete: 4c. -Plot the Mohr circle for each test and determine the values of cohesion and friction angle from your drawing. -A saturated specimen of the same clay was consolidated in the triaxial cell under a cell pressure of 75 kN/m² (drained conditions). The drainage valve was then closed and a deviator stress was gradually increased from 0 to 80 kN/m² under undrained conditions when failure occurred. Estimate the value of pore water pressure at failure? 4d. Plot the obtained results using a stress path approach (p' and q') and determine the values of cohesion and effective friction angle. Provide your working out below; add more pages if necessary Section 4. Stability issues related to the embankment construction As the alluvial clay is soft, the placement of a 3-m sand embankment may cause some stability issues (Figure 5). To estimate the stability of the sand embankment, samples of sand (Sample 1) and the alluvial clay (Sample 2) were collected for testing. You are required to estimate the strength characteristics of these soils. Note that these strength parameters (cohesion and friction angle) are necessary for slope stability analysis. Alluvium Embankment Sample 1 Sample 2 Failure plane Sandstone Figure 5. Potential failure plane in the alluvial clay due to the placement of the fill Sample 1-Embankment sand Table 7: Data from a series of shear box tests on Sample 1. Material: Sand Sample area: 20 cm² Normal Force, IN 0.18 0.33 0.79 1.18 Test N. 1 3 Shear force at failure, kN 0.09 0.16 0.41 Embankment 0.58 Tasks to complete: 4a. Plot the shear box test results obtained for the sand samples (Table 7) and determine the shear strength parameters of this soil. Using the obtained shear strength parameters, estimate the factor of safety for the slope, which is schematically shown in Figure below. Use the following data: Failure plane Conditions: at the end of embankment construction (water seepage parallel to the slope) h-2m B-38° Data on density and water content of the embankment sand is given in the beginning of Section 3 4b. Use the shear strength parameters from Q4a. A and B parameters of this saturated sand are 0.85 and 0.97 respectively. A triaxial sample of this soil is consolidated under a cell pressure of 200 kN/m² and back pressure (pore water pressure) of 100 kN/m². Once the consolidation was completed, the sample was sheared under undrained conditions by applying a vertical load. What would be the principal stress difference and pore water pressure at failure? Provide your working out below; add more pages if necessary Sample 2-Alluvial silty clay A series of consolidated drained triaxial tests were performed on the alluvial clay specimens and the obtained results are summarized in Table 8.1 Table 8: Results of triaxial tests on Sample 2. Test N. Confining Pressure, kN/m² 50 100 200 2 3 Deviator stress at failure q, kN/m² 129 163 Tasks to complete: 4c. -Plot the Mohr circle for each test and determine the values of cohesion and friction angle from your drawing. -A saturated specimen of the same clay was consolidated in the triaxial cell under a cell pressure of 75 kN/m² (drained conditions). The drainage valve was then closed and a deviator stress was gradually increased from 0 to 80 kN/m² under undrained conditions when failure occurred. Estimate the value of pore water pressure at failure? 4d. Plot the obtained results using a stress path approach (p' and q') and determine the values of cohesion and effective friction angle. Provide your working out below; add more pages if necessary