3. A square group of 9 piles is arranged in 3 rows and 3 columns spaced at 3 m centre- to-centre. The bored cast-in-situ

[answerhappygod]

3 A Square Group Of 9 Piles Is Arranged In 3 Rows And 3 Columns Spaced At 3 M Centre To Centre The Bored Cast In Situ 1 (201.94 KiB) Viewed 22 times

3. A square group of 9 piles is arranged in 3 rows and 3 columns spaced at 3 m centre- to-centre. The bored cast-in-situ concrete piles have a diameter of 600 mm and are embedded 6 m in a deep layer of stiff clay, which has a unit weight of y = 20 kN/m³. The pile group has a rigid cap. The elastic modulus of the pile material can be taken as Ep = 2000 MPa. Show full working out in the answer booklet and justify any assumptions that you made in answering both questions below. (a) Data from a pile load test conducted under undrained conditions indicated that the ultimate side resistance of a single pile was P, = 586.56 kN. Calculate the short-term allowable axial capacity of the pile group if the design requirement is a minimum factor of safety of 2. You may assume that the critical condition for the ultimate pile group capacity is the sum of the ultimate capacity of the individual piles with a group efficiency of 1.0, and hence, the analysis of the block capacity can be ignored. (7 marks) (b) Data from the same pile load test also indicated that 6.3 mm of settlement occurred for a single pile when a load of P = 400 kN was applied. Determine the settlement of the rigid pile cap, assuming that a total load of 3600 kN is applied to the pile cap. (Hint: An iterative approach may be required. Consider an initial guess for the elastic modulus of the soil as Es = 10 MPa.) (8 marks)