竖向荷载作用下盾构开挖引起的桩身竖向响应分析

Analysis of Vertical Response of Pile Body Caused by Shield Excavation Under Vertical Load

为研究竖向荷载作用下盾构开挖引起的邻近桩身轴力及竖向位移变化规律,以郑州某地铁侧穿桥梁桩基为工程背景,采用现场实测和数值法研究了盾构施工对邻近桩基竖向响应的规律,分析了隧道埋深、桩基上竖向荷载对竖向响应的影响.结果表明:无竖向荷载时桩身竖向位移沿深度逐渐减小,拱顶上方桩轴力随着深度逐渐增大,隧道中心线处最大轴力约500kN,而在隧道下方轴力逐渐减小.桩顶竖向荷载小于1000kN时,桩身竖向变形较小;大于1000kN时,隧道中心线以上桩身竖向变形较大.桩顶竖向荷载2000kN时,隧道埋深从12m增大至24m,桩顶最大竖向位移从7.5mm减小为4.2mm.隧道埋深小于18m时,桩身轴力呈现先缓慢增大再急剧减小最后再缓慢减小的三段式规律,隧道埋深达24m时,桩身轴力大致呈现出线性减小的规律.

In order to study the variation of axial force and vertical displacement caused by shield excavation under vertical load,a pile foundation of a side through bridge of Zhengzhou Metro is chosen as the engineering background.The vertical response of shield construction on adjacent pile foundation is studied by field measurement and numerical method,and the influence of the tunnel depth and the vertical load on the pile foundation on the vertical response is analyzed.The results show that the vertical displacement of the pile body without vertical load decreases along depth,and the axial force of the pile above the vault increases along depth.The maximum axial force at the center line of the tunnel is about 500 kN,while the axial force under the tunnel decreases gradually.When the vertical load of pile top is less than 1000 kN,the vertical deformation of pile body is smaller,and when it is greater than 1000 kN,the vertical deformation of pile body above the tunnel centerline is larger.When the vertical load of pile top reaches 2000 kN,the buried depth of tunnel increases from 12 m to 24 m,and the maximum vertical displacement of pile top decreases from 7.5 mm to 4.2 mm.When the depth of the tunnel is less than 18m,the axial force of the pile body presents a three-stage rule,i.e.increasing slowly at first,then decreasing rapidly and decreasing slowly at last.When the depth of the tunnel reaches 24m,the axial force of the pile body approximately presents a linear decreasing rule.