随钻跟管桩钻孔卸荷与后注浆效应的试验研究

Experimental study on unloading and grouting effects of DPC pipe piles

为了克服管桩施工的挤土效应,研发了钻进成孔、同步沉桩和后注浆的嵌岩非挤土大直径随钻跟管桩。通过足尺寸原位试验,测试了钻孔沉桩和桩侧注浆施工引起的桩周土体变形及压力变化情况,分析了钻孔卸荷和后注浆效应沿水平方向和深度方向的变化规律,揭示了随钻跟管桩施工对桩周土体的扰动。此外,基于圆孔收缩理论提出了随钻跟管桩钻孔卸荷变形预估方法。研究表明,随钻跟管桩的施工扰动主要表现为钻孔卸荷效应和桩侧后注浆效应,钻孔卸荷使孔壁收缩3.5~18.9mm,后续的桩侧注浆使收缩变形恢复了28%~50%,部分消除了钻孔卸荷效应的影响。修正后的圆孔收缩理论,可预估钻孔卸荷引起的桩周土体径向位移及压力变化。与锤击/静压管桩及中掘法管桩的挤土效应相比,随钻跟管桩的钻孔卸荷效应小,在城市建筑和管线密集区域应用更具优势。

To overcome the squeezing effect of pipe pile construction, a drilling with a prestressed concrete(DPC) pipe pile with drilling into hole, synchronous sinking pile and post-grouting was developed. It was a type of the rock-socketed and non-squeezed pipe pile. In this paper, the deformation and pressure change in the soil around the pile, caused by the drilling unloading and side post-grouting, were tested by in-situ tests. Based on test results, the change rules of unloading and grouting effects along the horizontal and vertical directions were analyzed, revealing the disturbances of soil around the pile. Moreover, a method for estimating the disturbances of DPC pipe pile construction was developed based on the circular hole shrinkage theory. The study shows that the disturbances mainly manifests unloading and grouting effects. Drilling unloading causes a shrinkage of the hole wall of 3.5-18.9 mm,and subsequent pile side post-grouting restore the shrinkage deformation by 28% to 50%, partially eliminating the impact of drilling unloading effect. In addition, the deformation and pressure change of soil around the pile caused by drilling unloading can be estimated by the modified circular hole shrinkage theory. Compared with the squeezing effect of displacement piles, the unloading effect of DPC pipe piles is significantly smaller, more advantages in application in urban areas with dense buildings and pipelines.