盾构下穿既有地铁隧道环向围压及受力变化

Changes in circumferential pressure and stresses in existing tunnels caused by tunnel crossing

为研究盾构近距离下穿对既有隧道管片环向内力的影响,综合考虑盾构正面附加推力、侧摩阻力、盾尾附加注浆力及土体损失4个因素在水平及竖直方向上产生的附加应力,提出一种既有隧道在附加应力作用下的围压重分布模型,推导了既有隧道环向围压的计算公式,利用修正惯用法计算了相应围压作用下的衬砌内力。结合具体工程案例,研究了盾构下穿前后既有隧道的环向围压、弯矩、轴力及剪力的变化,分析了下穿盾构埋深、盾构掘进位置及研究断面变化对环向围压的影响规律。研究结果表明:盾构下穿会引起既有隧道环向围压、弯矩、剪力和轴力减小;随着盾构埋深增加,既有隧道受到的附加围压及弯矩的影响逐渐减弱,且减小速度逐渐放缓;在穿越过程中,既有隧道受到的影响先增大、后减小,且在隧道上下拱顶位置的附加围压及弯矩变化较大;当既有隧道上的断面逐渐远离穿越中心点时,环向附加围压的分布模式由"竖椭圆分布"逐渐变为"横椭圆分布"。

In order to study the influence of shield tunneling on the annular internal force of the existing tunnel segments,the influence of additional stress on the horizontal and vertical direction caused by four factors including frontal thrust,lateral friction resistance,shield tail grouting force and soil loss was comprehensively considered.A re-distribution model of confining pressure for existing tunnel under the action of additional stress was presented.The internal force of lining under the appropriate confining pressure was calculated by the modified conventional method.The changes of circumferential confining pressure,bending moment,axial force and shear force of the existing tunnel before and after shield tunneling were studied.The influence of the buried depth,the tunneling position and the study section on the circumferential confining pressure of the existing tunnel was analyzed.The results show that shield tunneling can reduce the annular confining pressure,bending moment,shear force and axial force of the existing tunnel.With the increase of the buried depth of shield,the effects of additional confining pressure and bending moment on the existing tunnel are gradually weakened,and the reduction speed gradually slows down.In the process of crossing,the influences on the existing tunnel increase firstly and then decrease,and the additional confining pressure and bending moment at the top and bottom of the tunnel change greatly.When the section on the existing tunnel is gradually away from the crossing center,the distribution mode of circumscribed additional confining pressure changes from vertical elliptical distribution to horizontal elliptical distribution.