不同地层DX桩盘周土体附加应力分布研究

通过4组24根DX桩的破坏性模型试验，对承力盘分别位于砂土、粘土层中的DX桩进行静载试验对比，系统研究了DX桩盘周土体竖向附加应力分布规律及上下承力盘位于不同土层条件下DX桩盘周应力传递特性。结果表明：（1）加载过程中，DX桩盘周土层均承担了较大的荷载|（2）在砂土、粘土交互地层中对DX桩进行加载时，在上部砂层下部粘土层中上、下盘承担荷载近似相等|而在上部粘土层，下部砂性土层土层中上盘承担的荷载较小，下盘承担的荷载较大|（3）承力盘间距较小，会造成承力盘之间土体的整体剪切破坏，使DX桩桩身整体下移，大大降低其承载力。基于试验及理论分析，建议承力盘设计时竖向中心间距：当持力层为砂土时，不宜小于2倍盘径|当持力层为粉粘土时不宜小于1倍盘径。

Experimental study on the distribution of additional stress in soil around the bulbs

Destructive model tests of 4 groups of 24 DX piles were conducted and comparisive analysis were made about DX piles which set bulbs in sand and clay stratum in order to study the distribution of vertical additional stress in soil around the bulbs and evaluate the load transfer characteristics of DX pile when the bulbs were in different soil strata. The results showed that: (1) Significant amount of the applied load was carried by the soil strata around the bulbs of DX pile in the loading process| (2) After the DX pile in interbeded strata was loaded, the load carried by the upper and lower bulbs were almost identical in the condition that the upper stratum was sand and lower stratum was clay| however, when the clay stratum was underlain by sand stratum, the load carried by the lower bulb was much higher than the upper one| (3)Complete shear failure would occur when the distance between the two bulbs was excessive small, which led to the overall settlement of DX pile and reducement of bearing capacity. The proper vertical distance between two bulbs was suggested based on experimental and theoretical analysis: the value should be larger than two times of the bulb diameter when the bearing stratum was sand and a diameter when the bearing stratum was clay.