围护桩墙施工对隧道影响规律及净距控制分析

Analysis on the influence law and net distance control of retaining pile wall construction on adjacent shield tunnel

围护桩(墙)施工主要包括成孔(槽)、泥浆护壁、混凝土浇筑及硬化等环节,周边土体经历复杂的加(卸)载过程,产生的附加应力(位移)场会对邻近盾构隧道产生不利影响。本文对软土地区桩墙施工对紧邻盾构隧道的影响机理进行了初步研究,对实际工程案例进行了统计分析。采用有限元法对钻孔灌注桩和地下连续墙进行模拟,提出了不同的桩长、桩径(墙厚)及土层弹性模量下既有隧道变形控制指标为1~5mm时桩墙施工净距控制值。研究结果表明:首先,桩(墙)施工会造成周边土体位移,从而使得隧道结构发生约0~2mm的变形;其次,随着桩(墙)长、桩径(墙厚)的减小或土层弹性模量的增加,桩墙施工对隧道结构的变形影响逐渐减弱,其中土层弹性模量对隧道变形的影响最为明显;最后,施工净距控制值与桩径(墙厚)呈正相关关系,与土层弹性模量呈负相关关系。隧道变形控制指标为1~5mm时的钻孔灌注桩净距控制值在5~15.5m之间,地下连续墙净距控制值在5~30m之间。

The construction of the retaining pile(wall)mainly includes the links of hole forming(groove),mud retaining wall,concrete pouring and hardening,etc.The additional stress(displacement)field generated by the surrounding soil undergoing complex loading(unloading)process will have adverse effects on the adjacent shield tunnel.The influence mechanism of pile wall construction on adjacent shield tunnel in soft soil area is preliminarily studied,and the practical engineering cases are statistically analyzed.The finite element method is used to simulate the bored pile and underground continuous wall,and the control value of pile wall construction clearance under different pile length,pile diameter(wall thickness)and soil elastic modulus is proposed for the control index 1~5mm of the exist tunnel deformation.The study results show that the pile(wall)construction will cause the displacement of the surrounding soil,so that the tunnel structure occurs about O~2mm deformation;with the decrease of pile(wall)length and pile diameter(wall thickness)or the increase of soil elastic modulus,the influence of pile wall construction on the deformation of tunnel structure is gradually weakened,and the influence of soil elastic modulus on the deformation is the most obvious;the construction net distance control value is positively correlated with the pile diameter(wall thickness)and negatively correlated with soil elastic modulus.The control value of the net distance of the bored pile is between 5~15.5m when the deformation control indexes of tunnel are 1~5mm,and the control value of the net distance of the underground continuous wall is between 5~30m.