考虑管片环间接头弱化的新建隧道上穿引起既有盾构隧道纵向变形分析

Analysis of longitudinal displacement of existing shield tunnel due to construction of above-crossing new tunnel considering the weakening of circumferential joint

探究新建隧道上穿引起既有盾构隧道的纵向变形规律,对进一步评估并减少新建隧道施工对既有盾构隧道的不利影响具有重要的现实意义。现有解析方法多是将既有盾构隧道简化为搁置于线弹性地基上的等效连续梁,不能考虑隧道管片环间接头的弱化和土体非线性变形特征。首先,引入接头非连续盾构隧道模型和非线性Pasternak地基模型来考虑隧道管片环间接头的弱化及隧道–地基的非线性作用,推导得到新建隧道上穿开挖下既有盾构隧道纵向变形控制微分方程;其次通过有限差分法和牛顿迭代法求解得到既有盾构隧道纵向变形的数值解答;最后,对2个工程案例及常用等效连续梁模型对比验证。研究结果表明:等效连续梁模型计算得到的隧道纵向变形表现为连续特征,而所提方法考虑了隧道接头弱化作用,得到的隧道纵向变形表现为非连续特征,隧道纵向位移和弯矩在接头处会发生突变。通过参数分析可知,增加新旧隧道间净距可有效减少既有盾构隧道的隆起变形、弯矩和环间接头张开量;随着管片长度增加,既有盾构隧道的隆起位移略有减少,但是管片间环间张开量及弯矩随之增大;增加环间接头的刚度可有效减少既有盾构隧道的竖向位移和张开量,但是会导致隧道弯矩增加。

Exploring the longitudinal deformation mechanism of the existing shield due to construction of new tunnel above is significant to assess the adverse impacts of above-crossing tunnelling on the existing shield tunnel.Current analytical methods commonly simplify the existing shield tunnel as an equivalent continuous beam resting on a linear elastic foundation,of which will overlook the weakening of circumferential joint and the nonlinear deformation characteristics of the ground.Firstly,the joint discontinuous shield tunnel model and the nonlinear Pasternak foundation model are adopted to consider the weakening of circumferential joint and the tunnel-soil nonlinear interaction.The differential equation for shield tunnel longitudinal deformation owing to above-crossing tunnelling is derived.Secondly,the numerical solution for shield tunnel longitudinal deformation is solved using the finite difference method and the Newton’s iteration method.Finally,the predictions from the proposed method are compared with two field cases and the results predicted by the current equivalent continuous beam model.It shows that the longitudinal deformation and the bending moment based on the equivalent continuous beam model express continuous characteristics.While the longitudinal deformation and the bending moment predicted by the proposed method can reflect the discontinuous characteristics,because the weakening of circumferential joint is considered by the proposed method.The results obtained by the proposed method is much closer to the real shield tunnel deformation characteristics.Through the parametric analyses,it is found that increasing the clearance distance between the new and old tunnels will effectively reduce the tunnel heave,bending moment and joint opening.By increasing the length of segment ring,the tunnel heave will decrease slightly,but the joint opening and bending moment will increase.To increasing the stiffness of the circumferential joint will effectively lead to the decrease of tunnel vertical displacement and opening of joint,but it will increase the bending moment of tunnel.