Experimental investigation of the distribution of stresses in large bored situ-cast piles

Abstract

1. Diagrams were obtained of the distribution of specific skin friction of bored situ-cast piles with a diameter of about 1 m and length of 18 m and of their transformation as a result of flooding the soils and successive loading of the pile with gradual involvement of shearing resistance forces in a downward direction. 2. Before the long bored situ-cast piles broke loose, the specific skin friction in homogeneous soil is practically constant over the length of the pile, which confirms the correctness of the concept used in [3]. 3. On flooding soils at the base of the piles, when the external load is equal to zero and there is still no slumping of the soil layers under their own weight, substantial normal stresses occur in the cross sections of long bored situ-cast piles, as a result of which they are additionally loaded by the soil hanging on them. 4. The foot of long bored situ-cast piles penetrating loose layers of loam soils and supported on a layer of loam with e=0.662 carried no more than 10% of the total load applied to the pile prior to breaking loose. Thus it behaves as a friction pile before breaking loose. 5. After the pile breaks loose, the normal contact stresses on its foot increase in direct proportion to settlement. It follows from this that to increase the point resistance before breaking loose it is necessary to preliminarily compact the bottom of the hole of the bored situ-cast pile.