The Behaviour Of Long-short-pile Compsite Foundation With The Upper High Building Unedr Horizontal Loads——the Impact Of Cushion Modulus, Long-pile Modulus And Short-pile Modulus On The Bearing Behavior Of Long-short-pile Composite Foundation

In this paper, a3-D whole elastic-plastic model of high-rise building long-short-pile composite foundation was established to research the behavior of composite foundation under horizontal load. By analysing the impact of cushion modulus, long-pile modulus and short-pile modulus on the stress and settlement of foundation, comparing the vertical stress and horizontal stress, some significant conclusions are obtained as follow:(1) Stress distribution:the stress on both sides is bigger than in the middle, the stress distribution looks like U-shaped or saddle-shaped. Because of the horizontal load, the stress at the right side is bigger than the left. The whole distribution is uneven. Considering the impact of horizontal load, bearing capacity of composite foundation withn7m near the leeward side of the edge should be strengthen. design right side of the role of the horizontal load, should strengthen. The stress of long-pile at both ends is smaller than in the middle. The stress on the top of the short-pile is greater than at the end of short pile obviously. Soil-stress at the both ends is greater than in the middle.The distribution of soil-stress is opposite of the stress of long-pile.(2) By comparing of the horizontal stress distribution and the vertical stress distribution, vertical stress is much greater than horizontal stress. Pile plays a more important role in bearing vertical load than bearing horizontal load. The rest were the same.(3) Settlement rules:the settlement of raft at the right side is much bigger than the left side. The settlement of both pile and soil increases from the left to right linearly on section A-A. The maximum value in the X=15m is much bigger than the minimum value. The settlement on both sides is bigger than in the middle on section B-B. Pile settlement distribution is linear and soil settlement distribution is dentate.(4) Pile displacement distribution rules:the average displacement on the top of pile is positive and greater than at the end of short-pile. The average displacement on the end of long-pile is negative.Back row pile top displacement is maximum and positive, the pile-end displacement is minimum and negative, the distribution looks as arc;middle row pile top displacement is positive, the pile-end displacement is maximum, the middle is small, the distribution is linear; front row pile displacement is positive, the pile-end displacement is maximum. the middle is small.(5) The impact of cushion modulus:it only impacts the stress of pile and soil on the top of pile. With the increasing of cushion modulus, the stress of long-pile on the top increases, by the converse, soil stress decreases.(6) The impact of long-pile modulus:it affects long-pile stress and the pile-soil distribution ratio of load greatly. With the increasing of long-pile modulus, the uneven stress distribution is apparent due to horizontal load, the long-pile stress increases, the stress of short-pile and soil reduces, the settlement of raft reduces, the settlement of pile and soil decreases greatly, differential settlement between different planes increases. Long-pile modulus impacts front row pile and back row pile greatly.(7) The impact of short-pile modulus:it only impacts the stress on the top of pile and at the end of short-pile. With the increasing of short-pile modulus, the short-pile stress increases greatly and the stress of long-pile and soil decreases.