Sub - Section (A4) - 100 marks In a geotechnical project, Engineers are to drive two sheet piles 8 m away from each other and 4 m into a permeable sand layer as shown in Figure (A4-1). The sand layer is located on top of an impermeable rock and had a saturated unit weight of 19.3 kN/m2 and permeability value of 0.0007 m/sec. You are required to: Water level Water level 5 m Water level 5 m 2 m 8 m 14 m - 1 m C 4 m 1 1.5 m 3 m 1 8 m 4 m 4 m B 5 m 9 m Permeable Sand -2 m Impermeable Rock 24 m Figure (A4-1): Arrangement of sheet piles on sand layer (NOT to scale) 1) Draw the flow net around the sheet pile and determine the safety factor of the sheet pile (only left one for the safety factor determination) against boiling. 2) What will be the filter thickness to increase the safety factor (left sheet pile) against boiling to 4.5 (filter saturated unit weight is 24.4 kN/m)? 3) Plot the pore water pressure diagrams along lines AB and DC as per below information and Figure (A4-1): 6 a. Pint (A) is located 3 m below the soil surface and 1.5 m from the left sheet pile in horizontal direction b. Point (C) is located 1 m below the soil surface and 4 m from the left sheet pile in horizontal direction, and c. Lines (AB) and (CD) are horizontal and vertical lines, respectively. 4) Assuming that Engineers will use one pump in every 15 m along the sheet piles, determine the capacity of pump in m?/s to keep the downstream dry