富水地层盾构掘进下近接桩-土力学响应分析

基于富水地层透水性强、土层强度低等特性,运用盾构技术进行隧道施工造成的土层变形、临近桩体扰动等负面现象尤为突显。为探明渗流影响下由盾构掘进引起的孔压变化、桩-土响应规律,以某盾构隧道工程为依托,采用有限元数值分析方法,阐明盾构隧道在流-固耦合作用下的孔压分布、桩-土内力及位移发展形式。研究结果表明:(1)与未考虑地下水作用相比,渗流场影响下的桩体与地表土层沉降明显加剧,其沉降最大增幅分别达32.18%、31.95%;(2)盾构隧道下穿建筑桩基施工,对桩体内力值影响较大,桩体下部轴力沿埋深增长并产生负摩阻力,较大程度地抑制桩体性能发挥;(3)隧道防水失效下,周边围岩内部孔隙水压力于1倍隧道直径范围内呈现剧烈衰减,并沿水平向出现明显孔压降压带。

Analysis of Mechanics Response of Adjacent Piles-Soil under Shield Excavation in Water-rich Stratum

Due to such characteristics as strong water permeability and low soil strength of the water-rich stratum,the negative phenomena such as soil deformation and adjacent pile disturbance caused by tunnel construction with shield technology are particularly prominent.In order to ascertain the change of pore water pressure and the pile-soil response caused by shield excavation under the influence of seepage,the finite element numerical analysis method is used according to some shield tunnel project in Nanchang to illustrate the pore water pressure distribution,pile-soil internal forces and displacement development forms of shield tunnels under the fluid-solid coupling effect.The results show that:1) Compared with the one with no consideration of groundwater effect,the sedimentation of pile foundation and surface soil layer is significantly intensified under the influence of seepage field,and the maximum increase of sedimentation can be 32.18% and 31.95% respectively;2) The shield tunnel constructed underneath pile foundation in the building has a great impact on the internal force of the pile.The axial force of the lower part of the pile gradually increases along the buried depth and generates negative frictional resistance,which greatly inhibits the performance of the pile body;3) In case of inefficient tunnel waterproofing,the internal pore water pressure of the surrounding rock shows a sharp attenuation in the range of one-time tunnel diameter,and an obvious pore water pressure drop zone appears along the horizontal direction.