新建隧道近距离上穿对既有地铁隧道纵向变形影响分析

Analysis of longitudinal displacement of existing metro tunnel due to construction of above-crossing new tunnel in close distance

新建隧道近距离上穿施工会改变地层既有平衡应力场,引起地层应力释放,导致既有下卧隧道产生纵向隆起变形。提出了在新建隧道卸荷作用下估算既有隧道纵向变形的解析解答,既有隧道简化为搁置于Pasternak地基上的Euler-Bernoulli梁,采用两阶段分析法分析求解。首先,通过Mindlin弹性力学经典解估算新建隧道开挖卸荷引起在既有隧道位置处的竖向附加分布荷载;其次,建立在竖向附加荷载作用下的隧道纵向变形平衡微分方程,并基于有限差分原理,获得隧道变形数值解答。经与已报道的两个工程实测结果对比发现,理论计算结果与实测数据较为吻合,基本可以反映在新建隧道近距离上穿施工过程中既有隧道的纵向变形规律,从而验证其解析解答正确性。

New tunnel crossing over existing tunnel will inevitably change the already balanced ground stress field and cause ground stress relief, which will result in longitudinal heave of existing underlying tunnel. An analytical method is proposed to assess the longitudinal displacement of the existing tunnel subjected to above-crossing tunneling. The existing tunnel is simplified to be Euler-Bernoulli beam resting on the Pasternak foundation model. Two-stage analysis method is adopted to analyze this problem. First, the vertical distributed unloading load induced by the construction of above-crossing tunnel is computed by Mindlin′s solution. Second, equilibrium differential equation is established under the corresponding vertical distributed load due to unloading and it is solved numerically based on the finite difference method. The applicability of the presented method is validated against two well-documented case histories. A consistent trend between the measurements and predictions is observed. It means the proposed method can be reasonably reflect the law of the longitudinal displacement of existing tunnel subjected to above-crossing new tunnelling in close distance.