浅埋盾构隧道开挖面失稳发展过程模型试验

Model test of evolution of face instability in shallow shield tunnel

为了研究开挖面支护力、地层变形规律和开挖面失稳发展过程,利用对称性,采用半隧道模型,进行不同支护板后退速率下的4组试验.结果表明,支护板后退速率影响支护力和地层变形数值,而不影响其发展规律.随着支护板位移增大,支护力快速下降到最小值,接着上升到稳定值.相应地,开挖面失稳发展依次经历局部剪切带、闭合剪切带、贯穿剪切带3个阶段.与理论模型的对比发现,机动场模型处于闭合剪切带阶段,得到的支护力更接近于最小支护力;楔形体模型处于贯穿剪切带阶段,得到的支护力更接近于稳定支护力.

Symmetry and semi-tunnel model were introduced to conduct four tests for various back rate ofthe support panel in order to analyze support pressure on the excavation face, ground deformation and theevolution of the face instability. The back rate of the support panel affects the value of support pressureand ground deformation without affecting their development law. With the increase in the facedisplacement, the support pressure dropped steeply to the minimum value, then increased to a steadystate. Correspondingly, the instability development undergoes localization shear band, closed shear bandand throughout shear band. Compared with theoretical models, the kinetic field mode is located in theclosed shear band stage, when the support pressure is similar to the minimum value in tests. The wedgemode is located in throughout shear band stage, when the support pressure is similar to the stable value intests.