为研究路堤荷载下刚柔长短桩复合地基的承载特性，结合某桥头过渡段带帽薄壁管桩（pre-stressed thin-wall concrete，PTC）联合水泥土搅拌桩（cement deep mixed，CDM）的软基处理工程，开展了PTC-CDM组合式长短桩复合地基承载特性现场试验，对路堤填筑过程中桩土应力比、荷载分担比以及桩土沉降差的变化规律进行了分析，并进一步采用有限元对刚柔长短桩复合地基的路堤荷载传递规律进行了数值模拟．试验与计算结果表明：CDM桩顶与桩间土应力增长缓慢，PTC桩帽上应力增长相对较快；填土达到一定高度土拱完全形成后，大量的路堤荷载转移至刚性长桩；刚性长桩和柔性短桩的桩土应力比分别达到7．5和2．1；短桩的存在减少了长桩桩顶荷载和上部桩身出现负摩阻力的深度，中性点位置上移；短桩达到一定桩长时再增加其长度，对路基总沉降影响不明显，因此，短桩桩长可根据承载力要求的临界桩长来设计．%In order to study the bearing characteristics of the composite foundation with rigid-flexible and long-short piles under embankment loading,a field test of a foundation improved by the capped pre-stressed thin-wall concrete (PTC ) piles and soil cement deep mixed (CDM ) columns was conducted in a bridgehead transition section. The variation laws of pile-soil stress ratio,load sharing ratio and pile-soil differential settlement were analyzed. Furthermore,the embankment load transfer characteristics of long-short-pile composite foundation were numerically simulated. The test and simulation results indicate that soil pressure between piles and stress on the top of CDM pile increase slowly with the increase of embankment load,while the pressure on the top of PTC pile cap increases faster. Due to the effect of soil arching caused by differential settlements between the piles and the soil,a large part of embankment load is shifted to the rigid-long piles. And the maximum values of stress ratio between rigid-long pile as well as flexible-short pile and soil are 7. 5 and 2. 1,respectively. The location of the neutral point of rigid-long pile shaft gradually ascends up during the embankment filling and soil consolidation due to the existence of short piles,and the pile-top pressure and pile shaft friction resistance of rigid-long pile decrease. The change of short pile length makes no difference to embankment settlement when it becomes larger than a certain value. Therefore,the length of short pile can be designed to be the critical value that satisfies the requirement of ground bearing capacity.
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