Analysis on Negative Friction Segment of Pile-raft Composite Foundation and Calculation of Its Pile-soil Stress Ratio

The calculating method of the additional stresses in the inter-pile soil in the pile-top negative-friction segment of pile-raft composite foundation is obtained by analyzing the interaction of pile soil in the negative friction segment at the top of the pile.On this basis,the pile-soil-cushion interaction of the composite pile-raft foundation is simulated with the spring-set model,the calculating method of the vertical effective stresses of the pile and inter-pile soil on the pile-top plane and the penetration distance from the pile-top is created.The influence of cushion on stress regulation and settlement control is analyzed.The research results show as follows: Under the action of the friction between the pile and inter-pile soil,the vertical effective stress of inter-pile soil decays with depth and to a low level at a certain depth below which the influence of pile-soil interaction on the pile-soil stress ratio at the pile top can be neglected;the modulus of the cushion plays an important role in pile-soil stress adjustment at the pile top and exerts obvious influence on the penetration amount at the pile top;the smaller the modulus of cushion,the more the penetration amount,and the penetration amount growth accelerates along with decreasing of the modulus of cushion.