玄真观隧道高地应力整治段坍塌原因分析及处理措施

玄真观隧道贯通后，由于高地应力的原因导致隧道局部衬砌开裂变形，变形段衬砌需拆换整治。拆换过程中，对围岩的二次扰动，使隧道周边围岩产生较大的松动圈，地应力反复重新分布，局部应力高度集中，应力积聚值大于围岩极限强度时发生隧道坍塌。坍塌治理中，对坍塌影响段采取了方木垛、工字钢架临时支撑及预初支背后预注浆加固，防止坍塌的继续扩大；对坍塌段采取了机械手喷射混凝土封闭岩面、工字钢架护拱、预留孔道回填混凝土、加强初支及衬砌等技术措施，取得了坍塌处理的预期效果。

Cause Analysis of Collapse in High Geostress Regulation Section of Xuanzhenguan Tunnel and the Countermeasures

Xuanzhenguan Tunnel had local lining cracking and deformation caused by high geostress after opening. The lining in the deformed section was required to be replaced and regulated. During this process, the second disturbance to the surrounding rock made large broken zone therein and geostress be repeatedly distributed, thus local stress was concentrated highly, and when the stress accumulation is larger than the surrounding rock’s ultimate strength, there happened tunnel collapse. In the collapse treatment, the section affected by the collapse was supported temporarily by cubic crib and steel I-frame, and reinforced by pre-grouting at the back of primary support so as to avoid collapse from continuously expanding; and in the section attached by the collapsed, the technical measures, such as sealing rock surface by concrete spraying from mechanical arm, arch protecting by steel I-frame, reserving duct for concrete backfill, strengthening primary support, were used.The collapse treatment gets desired effect.