摘要：
The long-short-piles composite foundation technology can improve the bearing capacity of the foundation and reduce the settlement.This technology has good economiy and security,which has good prospects for development.According to the characteristics and the research situation of the technology,this paper discusses the main factors (the thickness of cushion,the length and replacement ratio of long piles,the length and replacement ratio of short piles,the upper structure stiffness) affecting the settlement and the load sharing ratio,and draws some useful conclusions.Cushion does not affect the differential settlement of raft,and the average settlement increase,slightly with the thickness of cushion.But there is certain limit.When the thickness of cushion is in a certain range,the load sharing ratio of long pile decreases significantly with the increase of the thickness of cushion layer,the soil mass increases significantly,and the load sharing ratio of short pile increases.If the thickness of the cushion continues to increase,the load sharing ratio tends to be stable.The influence of the length of long piles which are on the differential settlement of raft bottom is limited.But the increase is slow and the average settlement decreases.The load sharing ratio of long piles increases with the length of the long piles.But the soil mass and the short piles decrease in a certain limit.When the replacement ratio of long piles exceeds a certain range,the influence on the settlement of raft bottom and the load sharing ratio of pile-soil is not obvious.The length of short piles and replacement ratio of short piles have little influence on the settlement of raft bottom and the load sharing ratio of pile-soil.The structure stiffness has little influence on the differential settlement of the raft bottom and the load sharing ratio of pile-soil.The average settlement of the raft bottom increases with the structure stiffness,but then it increases slowly.This conclusions can provide a reference for the design and application of the long-short-piles composite foundation.%高层建筑长短桩复合地基技术既可以提高地基承载力,又可以减少沉降,经济性好、安全性高,有良好的发展前景.针对该技术的特点,作者参照近年来国内外的工程应用和研究情况以及自己的研究成果,确定了该技术的主要影响因素,主要为褥垫层厚度、长桩的长度及置换率、短桩的长度及置换率、上部结构刚度,并对这些因素在沉降和荷载分担比上进行探讨,得出有益结论.结论如下:褥垫层厚度对筏板底的差异沉降基本不影响,平均沉降则随之增大略有增加,但有一定的极限;当褥垫层厚度在一定范围内时,长桩荷载分担比随褥垫层厚度的增大而显著减小,土体显著增大,短桩荷载分担比有所增大,继续增加褥垫层厚度后,各部分荷载分担比趋于稳定;长桩长度对筏板底的差异沉降影响有限,其增幅缓慢,平均沉降则随之减小;长桩荷载分担比随长桩长度的增加而增大,土体和短桩则随之减小,但有一定极限;长桩置换率超过一定范围后,对筏板底沉降和桩土荷载分担比影响不明显;短桩长度和短桩置换率对筏板底沉降和桩土荷载分担比影响较小;上部结构刚度对筏板底差异沉降和桩土荷载分担比影响较小,筏板底的平均沉降随上部结构刚度增大而增大,随后增幅变缓.这些结论可为该类型复合地基的设计和应用提供参考.
