Finite Element Analysis On The Bearing Behavior Of High-Rise Building Long-Short-Pile Composite Foundation Under Horizontal Load

Long-short-pile composite foundation is a foundation treatment method that combines rigid long piles with rigid, semi-rigid or flexible short piles to bear upper load along with soil. As a new foundation treatment manner, long-short-pile composite foundation has been widely used in design and construction of high-rise building foundation treatment. The theoretical research on long-short-pile composite foundation of high-rise building under horizontal load lags far behind the engineering practice. In this paper, a 3-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, in which the value of horizontal load, thickness of cushion and length of long piles were taken into accounted. Conclusions were as follow:(1) With the increment of horizontal load value:The average settlement differentials of edge close to horizontal load and edge away from horizontal load of raft upper surface increased. The vertical load bore by long and short piles of different base regions changed related with their location. In the side that away from horizontal load, long piles always followed a law that the value of axial force of corner piles were the largest, followed side piles and then center piles, short piles always followed a law that the value of axial force of side piles were the largest, followed corner piles and then center piles. The horizontal displacement of cushion top and piles top increased. Piles at side close to horizontal load and side away from horizontal load of base bore more horizontal load than that of center. The horizontal load and moment bore by long and short piles of different base regions changed related with their location.(2) With the thickness of cushion increasing:The average settlement differentials of edge close to horizontal load and edge away from horizontal load of raft upper surface decreased. The vertical load distribution ratio of long piles decreased, while that of short piles and soil increased. The differentials of vertical load distribution ratio of long and short piles among different base regions decreased. In the side that away from horizontal load,whether with or without cushion long piles always followed a law that the value of axial force of corner piles were the largest, followed side piles and then center piles. Without cushion, short piles also followed the same law with long piles. After having paved cushion, the value of axial force of short side piles and short corner piles were far greater than that of short center piles. The horizontal displacement differentials between cushion top and piles top increased. The horizontal load distribution ratio of long and short piles decreased, while that of cushion and soil increased. There was a best cushion thickness to reduce the differentials of horizontal load distribution ratio of long and short piles among different base regions and harmonize the value of piles moment of different base regions.(3) With the length of long piles increasing:The average settlement differentials of edge close to horizontal load and edge away from horizontal load of raft upper surface decreased. The vertical load distribution ratio of long piles increased, while that of short piles and soil decreased. The vertical load distribution ratio of long and short pile at side close to horizontal load and side away from horizontal load of base increased, while that of center region decreased. In the side that away from horizontal load, long piles always followed a law that the value of axial force of corner piles were the largest, followed side piles and then center piles, short piles always followed a law that the value of axial force of side piles were the largest, followed corner piles and then center piles. The horizontal displacement differentials between cushion top and piles top basically unchanged. The total horizontal load distribution basically unchanged. The horizontal load distribution ratio of long piles at side close to horizontal load and side away from horizontal load of base increased, while that of center region decreased. The horizontal load bore by short piles of different base regions changed related with their location. Adding the length of long piles in a certain extent harmonize the value of piles moment of different base regions.