FRACTURING AND DEFORMATION MECHANISM OF SURROUNDING ROCK OF DEEP-BURIED AND HIGH IN-SITU STRESS HARD ROCK TBM TUNNEL

The deformation of surrounding rock in deep depth caused by high in-situ stress is a key factor that restricts the safe and efficient construction of TBM tunnel. As a result of deep depth,high in-situ stress,and hard rock,there are different kinds of failures in the surrounding rock after the excavation unloading. The failure pattern varies with time and the degree of stress concentration. It may cause vault settlement and arch bottom uplift,which greatly threaten the safety of construction personnel and equipment. The failure pattern and deformation of surrounding rock of Yin-Han-Ji-Wei water conveyance tunnel(K45+534.70-K45+701.92) are monitored and examined in this present paper. The process of surrounding rock failure is analyzed. The law of deformation of arch shoulder and vault is revealed,and the support measures for deformation of hard rock with high in-situ stress are put forward. As a result of tangential stress of surrounding rock,tensile-shear failure is mainly caused by splitting. The failures of surrounding rock include rock burst and static brittle failure(rib spalling,exfoliation,slabbing failure). The deformation of surrounding rock can be divided into three stages: rapid deformation stage,transitional stage and slow deformation stage. The deformation at initial two stages is about 60% ~80% of ultimate deformation. Accelerated deformation may occur two or three times in some conditions. The first acceleration is mainly caused by the opening cracks,the dilatation of rock slab and the partial flexion,which occurs quickly and lasts for a short time. However,the second acceleration deformation is mainly caused by the deflection of rock slab and the expansion of rock block. Its deformation speed is small but the duration is long. The surrounding rock support measures including NPR bolt,steel arch and steel fiber reinforced concrete are put forward,which provides engineering experience and theoretical basis for the safe and efficient construction of similar TBM tunnels.