Question

(22 marks) piles are to be constructed in a site with soil the ground surface) 2 m layer of new ilt, followed by 12 m layer of soft clay,f deep layer of dense the major sand. The Gwr is 0.5m below the ground surface geotechnical considerations for the piles (6 marks)

Answer 1

Basic considerations for end bearing pile in the given condition:

The soil profile of the given site condition is shown in the figure.

z 0.50 m 7 Fill Soil 2m Clay soil 12m Dense sand

1) It is specified as end bearing pile, the stress transfer takes place only at the base of the pile.

2) The pile usually transfer the load from the superstructure to the soil. The stress transfer happens along the sides and also at the tip of the pile. In our case, the pile transfers load only at the end.

3) Even though the sides of the piles also distributes the load as shown in the figure. But the fill material in the top layer of the soil profile settles. The settlement of the fill material imparts a downward force on the pile as shown in the figure.

Qu IBackfill settles End Bearing

4) The pile has to distribute the load from the superstructure and also the downward drag force created by the fill soil.   

Load acting on the pile = Load from the superstructure + drag force from the fill soil

Safe load-bearing capacity of pile = (Load from the superstructure + drag force from the fill soil)/Factor of safety

5) The end bearing of the pile lies in the sandy stratum. The stress transfer happens through the soil by friction. The friction depends on the surface nature of the soil and also effective stress.

Load carrying capacity of the pile = end bearing + skin friction

= End bearing ( skin friction not considered)

= (cross-sectional area) Bearing area * Effective stress * N_q