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Evaluating closely spaced twin-tunnelling-induced shear stiffness change by subsurface settlement in clayey ground
Environmental Earth Sciences ( IF 2.8 ) Pub Date : 2020-06-27 , DOI: 10.1007/s12665-020-09087-z
Fan-yan Meng , Ren-peng Chen , Huai-na Wu , Hong-zhan Cheng

Cases of closely spaced twin tunnels demonstrate that ground settlement above the 2nd tunnel, referred to as T2 constructed after the first tunnel (T1), exhibits pronounced differences from that above T1. The differences can be attributed to the disturbance induced by T1 construction. Based upon closed-form plasticity solutions for an unloading cylindrical cavity, this study employs subsurface settlement troughs to determine the shear modulus change during twin-tunnelling. Observations of 1 g model tests for twin-tunnelling in overconsolidated kaolin clay are interpreted from literature. After T1 construction, for positions with different radial distances but a constant angle with respect to the vertical line above the tunnel center, the graph of radial displacement/tunnel radius versus tunnel radius/radial distance exhibits good linearity. Further analyses demonstrate that the shear stiffness decreases as the angle increases. In comparison, during T2 construction, the shear modulus of soils close to T1 degrades, while the other side increases. In light of the observations of combined axial–torsional tests, the tendency of shear modulus change can be attributed to the rotation of principal stress axes. The findings can explain the differential settlements over closely spaced twin tunnels in clayey ground.

中文翻译:

通过黏土中地下沉降评估紧密间隔的双隧道引起的剪切刚度变化

密集双胞胎隧道的情况表明,第二条隧道上方的地面沉降(在第一条隧道(T1)之后构造为T2)与T1上方的地面沉降存在明显差异。差异可以归因于T1构造引起的干扰。基于卸载圆柱腔的闭合形式塑性解决方案,本研究采用地下沉降槽来确定双隧道期间的剪切模量变化。从文献中解释了1 g模型试验对超固结高岭土中双隧道的观察。在T1施工之后,对于径向距离不同但相对于隧道中心上方的垂直线的角度恒定的位置,径向位移/隧道半径与隧道半径/径向距离的关系图具有良好的线性。进一步的分析表明,剪切刚度随角度的增加而减小。相比之下,在T2施工期间,接近T1的土壤的剪切模量会降低,而另一侧会增加。根据轴向-扭转组合试验的观察结果,剪切模量变化的趋势可以归因于主应力轴的旋转。这些发现可以解释粘土质地基中近距离孪生隧道的差异沉降。
更新日期:2020-06-27
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