Question

Q2. A pile group consists of 9 solid floating piles in cohesive soil. Each pile's diameter (d) is 0.50 m and the centre-to-centre spacing (s) is 2.5 m. The subsoil consists of a thick deposit of stiff cohesive clay with an unconfined cohesion of 80 kPa. The total unit weight of soil is 17 kN/m3. The pile group efficiency is 0.83. d 0.5m 1.5m (a) Find the allowable load capacity of the pile group if the required factor of safety is factor is 3. (No need to check the block failure capacity of the pile group.) Section Not to Scale 11m (b) Find the settlement of the pile group if the plies and soil moduli of elasticity are 25 GPA and 25 MPa, respectively.

Answer 1

(a) number of piles = 9 cohesion (C) = 80 kpa Unit Weight of Soil (r_sat) = 17 kN/m^3 pile group Efficiency = 0.83 Efficiency of pile group (_r) = group carrying capacity of pile/individual pile load carrying capacity times 100 0.83 = Q_g/n middot Q_i times 100 (N_c = 9) Q_i = A_b middot CN_C + A_s alpha C A_b = Base area = B_a times L = 5.5 times 5.5 = 30.25 m^2 A_s = Surface area = 2 (B_0 + L_0) middot L = 2 (5.5 + 5.5) 12.5 = 275 m^2 Q_i = 30.25 times 80 times 9 + 275 times 80 = 43780 = 43.78 MN 100 times 0.83 = Q_g/9 times 43.78 times 100 = > Q_g = 350.67 MN Q_s middot Q_g/F = 116.9 MN \r\n b) group pile Settlement = squareroot B_g/ S middot d times H_ei H_ei = individual pile settlement H_i = Q middot L/A_p middot E_p