格栅状搅拌桩复合地基静载试验研究

Static Load Tests on Composite Foundation of Grid-shaped CDM Piles

为科学、合理地在砂土地基中进行高置换率栅状搅拌桩复合地基的设计和施工,在湖北汉江流域兴隆水利枢纽工程中,开展了格栅状搅拌桩复合地基静载荷试验研究。试验结果表明:1可将P-ΔS/ΔP试验曲线归纳为3个阶段,即桩侧阻力发挥的直线段、桩端阻力逐步发挥的调整变化段与桩端阻力完全发挥的破坏段;2采用P-ΔS/ΔP曲线比P-S曲线更能反映桩基刚度变化及其工作形状与荷载传递规律;3高置换率的口型砂基搅拌桩外侧摩阻力可全长发挥,其极限承载力主要受桩底砂性土密实状态下剪松破坏后的残余强度控制,属于典型的摩擦端承桩。

In order to realize the scientific and reasonable design and construction of composite foundation of gridshaped CDM（ cement deep mixing） piles with high-replacement rate in sand foundation,we carried out the static load tests on the composite foundation of grid-shaped CDM piles,Xinglong hydro-junction in Hanjiang River basin in Hubei provinceis taken as example. Result shows that 1） the P-ΔS / ΔP（ pressure vs. variation rate of settlement with pressure） curve of CDM piles can be divided into three sections,that is,the line segment of pile shaft resistance,the adjustment and change section of pile tip resistance and the failure section of pile tip resistance. 2） The curve of P-ΔS / ΔPcould better reflect the rigid variation and working behavior of the composite foundation of CDM piles than the curve of P-S（ pressure vs. settlement）. Moreover,the pile shaft resistance can be fully developed,which has mouth-shaped layout with high-replacement rate in sand foundation. The piles in grid shape are typical frictional end bearing piles as the limit bearing capacity of pile is mainly affected by the residual strength of bottom sandy soil in compacted state after shear failure.