QUESTION 1 (25 marks) Part A A lake is being reclaimed by lowering the water table below the bottom of the lake. The lakebed consists of 10 meters of homogeneous clay, having a saturated volumetric weight of 18 kN/m². Below the clay, the soil is sand having a saturated volumetric weight of 20 kN/m². Initially, the water level is 2 m above the soil surface, after the reclamation the groundwater level is 2 m below the soil surface, and it is assumed that the soil remains saturated. Construct graphs of total stresses, effective stresses and pore pressures before and after the reclamation to a depth up to 15m from the surface. The density of water is 10 kN/m³ (10 marks) Part B A sand sample of 25 cm in length was subjected to a constant head permeability in a permeameter having an area of 30 cm². A volume of 180 cm³ was obtained in 1 minute under a head of 39 cm. The mass of dry sand in the sample was 1,350 g. The specific gravity of the sand particles was 2.67. Darcy's equation can be written as q = Ak where A is sample area, h/L is hydraulic gradient, k is coefficient of permeability and q is the discharge. Determine, Part C 1. The coefficient of permeability 2. The discharge velocity, and (2 marks) (3 marks) 3. The seepage velocity (Hint: seepage velocity is discharging velocity multiplied by porosity. Porosity is the ratio of the volume of voids to the total volume of soil) (3 marks) In a falling head permeability test, the time taken for the head to fall from hi to h2 is t. If the test is repeated with the same initial head, what would be the final head in a time interval of t/2? The permeability equation in the falling head method can be written as follows where A, and L are soil sample dimensions, a is the standpipe cross-sectional area and At is the time for the standpipe head to decrease from h₁ to h₂. (7 marks) k = 2.303- al -10910 h₂ ΑΔΙ h₁ not 112 QUESTION 2 (25 marks) Part A Explain the difference between permeability and seepage by defining, comparing and contrasting each other. Separately list out at least three parameters (for each) which can affect permeability of a material and seepage through a medium. Part B (8 marks) Draw the typical flow net diagrams to following scenarios given in Figure 1 and Figure 2. (10 marks) Impervious Figure 1 - Concrete Gravity Dam with Down-Stream Seepage Barrier Sheet piles REV:00/0 Impervious Figure 2 - Double Sheet Pile Cut-off Dewatered Construction Well

QUESTION 1 (25 marks) Part A A lake is being reclaimed by lowering the water table below the bottom of the lake. The lakebed consists of 10 meters of homogeneous clay, having a saturated volumetric weight of 18 kN/m². Below the clay, the soil is sand having a saturated volumetric weight of 20 kN/m². Initially, the water level is 2 m above the soil surface, after the reclamation the groundwater level is 2 m below the soil surface, and it is assumed that the soil remains saturated. Construct graphs of total stresses, effective stresses and pore pressures before and after the reclamation to a depth up to 15m from the surface. The density of water is 10 kN/m³ (10 marks) Part B A sand sample of 25 cm in length was subjected to a constant head permeability in a permeameter having an area of 30 cm². A volume of 180 cm³ was obtained in 1 minute under a head of 39 cm. The mass of dry sand in the sample was 1,350 g. The specific gravity of the sand particles was 2.67. Darcy's equation can be written as q = Ak where A is sample area, h/L is hydraulic gradient, k is coefficient of permeability and q is the discharge. Determine, Part C 1. The coefficient of permeability 2. The discharge velocity, and (2 marks) (3 marks) 3. The seepage velocity (Hint: seepage velocity is discharging velocity multiplied by porosity. Porosity is the ratio of the volume of voids to the total volume of soil) (3 marks) In a falling head permeability test, the time taken for the head to fall from hi to h2 is t. If the test is repeated with the same initial head, what would be the final head in a time interval of t/2? The permeability equation in the falling head method can be written as follows where A, and L are soil sample dimensions, a is the standpipe cross-sectional area and At is the time for the standpipe head to decrease from h₁ to h₂. (7 marks) k = 2.303- al -10910 h₂ ΑΔΙ h₁ not 112 QUESTION 2 (25 marks) Part A Explain the difference between permeability and seepage by defining, comparing and contrasting each other. Separately list out at least three parameters (for each) which can affect permeability of a material and seepage through a medium. Part B (8 marks) Draw the typical flow net diagrams to following scenarios given in Figure 1 and Figure 2. (10 marks) Impervious Figure 1 - Concrete Gravity Dam with Down-Stream Seepage Barrier Sheet piles REV:00/0 Impervious Figure 2 - Double Sheet Pile Cut-off Dewatered Construction Well

Principles of Foundation Engineering (MindTap Course List)

8th Edition

ISBN:9781305081550

Author:Braja M. Das

Publisher:Braja M. Das

Chapter16: Soil Improvement And Ground Modification

Section: Chapter Questions

Problem 16.12P

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