预压荷载作用下砂桩复合地基承载力模型试验研究

Model experimental study on bearing capacity of sand pile composite foundation under effect of preloading

针对淤泥质土地层沉井基础采用砂桩地基处理后其地基承载力实测值远大于设计值的工程问题,结合砂桩施工过程以及沉井施工工艺,为定量研究附加荷载转换为有效应力压密了地层从而促进地基承载力的提高,根据载荷板试验的要求、最大影响深度以及砂桩置换率,自主设计了可重复利用能施加预压荷载的载荷板模型试验装置,并开展了相关试验研究。结果表明:本套装置利用轨道将模型箱滑入反力架的方法实现了预压后地基承载力测试的反复开展;本套装置可以稳定地施加预压荷载,方便地开展载荷板试验;在置换率为36%的砂桩复合地基在180 kPa预压荷载作用下,埋深0.8 m的桩间土11 d后孔压消散68%;桩间淤泥质土预压固结后地基承载力提高了约58%。对于地基承载力要求较高但容许地基有较大变形的临时工程,砂桩设计可采用该试验装置估算淤泥质土固结后承载力,从而达到减少置换率、节省工程造价的目的。

Aiming at the engineering problem of that the measured value of the foundation bearing capacity is far larger that its design value after treating the open caisson foundation in muddy soil stratum with sand-pile foundation, a reusable and preloading load plate model test apparatus is self-designed according to the requirement and the maximum affecting depth of the load plate test as well as the replacement ratio of sand-pile in combination with the construction process of sand-pile and the construction technology of open caisson, so as to study that the additional load is transferred into effective stress to compact the stratum and then promotes the enhancement of the foundation bearing capacity, furthermore, the relevant experimental study is carried out. The result shows that the test apparatus realizes the repeat test of the foundation bearing capacity after the preloading by the method of sliding model box into the reaction frame with track, thus can steadily apply preloading and conveniently make the load plate test. For the composite foundation with the sand-pile replacement ratio of 36% under the preloading effect of 180 kPa, the pore water pressure of the soil mass between piles with the embedded depth of 0.8 m is dissipated by 68% after 11 d,while the foundation bearing capacity after the preloading consolidation of the muddy soil between piles is increased by about 58%. For temporary foundation treatment project with higher requirement of foundation bearing capacity and larger allowable deformation, the bearing capacity after the consolidation of muddy soil for the sand-pile design can be estimated with this test apparatus, so as to get the target of reducing the replacement ratio and lowering the construction cost.