| With the wide use of tunneling technique, infrastructure construction has been continuously improved. At the same time, the application of the method has some difficult problems of technology. Two serious ones of them are rock burst in rock tunnel and the instability of excavation face in soil shield tunnel. A great deal of research on mechanism of rock burst has been conducted by many scholars. But up to now no consensus is formed to exactly predict rock burst. No mature theories have been identified from many researches about face stability of shield tunnel, especially in researching effect of groundwater seepage on tunnel face stability. So it is necessary to study mechanism of rock burst and face stability of tunnel. The main work is as follows:(1) The stress and strain state of tunnel surrounding rock is an important basis for analysis of stability of surrounding rock. Elastoplastic analysis of surrounding rocks of deep tunnel is carried out by non-linear Hoek-Brown yield criterion. The analytical equation for calculating the stress around openings is proposed. The stress state of surrounding rocks is also given.(2) Then a model of crack situated close to the straight boundary is established. The stages of crack growth are researched by using the dipole asymptotic method. When the crack is close to the free boundary, analysis of crack near circular arc boundary under biaxial compression is conducted with considering the influence of the boundary shape. The critical stress condition corresponding to the onset of the unstable growth of crack nearby free boundary is obtained. This condition is the critical stress level of rockburst.(3) Three-dimensional numerical simulation on shield tunnel is carried out by FLAC3D. The influence of groundwater seepage and strain softening in soils on limit supporting pressure, displacement, plastic zone of excavation face and ground settlement is analyzed. Effect of seepage on face stability is also discussed. The results show that seepage can easily lead to instability of excavation face, and also cause the limit support pressure to build up.(4) The research results of face stability are applied to actual engineering, e.g. the line 9 of Tianjin metro. The deformation of soil in front of face during tunneling is studied by considering seepage force. The support pressure range used in construction of this engineering is predicted according surface subsidence. And the results of prediction agree well with the actual monitoring values. |
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