Model Test Study On The Tunnel Within Cracked Surrounding Rocks

On the study of tunnel excavation, physical simulation can effectively simulate the nonlinear characteristics during failure of surrounding rocks. In accordance with the choice of model material in general principle, the dissertation obtains a set of model materials by 10 series of different mixture material mechanics test that simulate reliably the surrounding rock I, II, III in order to build physical model in cracked surrounding rocks.For the construction of single-arch tunnel within cracked surrounding rocks, 8 tunnel models are set up to study the effect of the earth pressure distribution of the various surrounding rocks due to excavation. The relationships between the loosen zone of tunnel radial earth pressure and the tunnel diameter, the characteristics of surrounding rocks and the exposed time are revealed. It is showed that the pressure loosen radius is 1.2~2.0 tunnel diameters and the strongly loosen radius drops to 0.5~ 1.0 one for double lane tunnel. The earth pressure curve and bending moment curve on lining versus the prop time are presented. The anchor reinforce effect in various rocks is analyzed and the reasonable support time for cracked surrounding rocks is put forward. And then the features of the tunnel deformation failure in various rocks are discussed by the breakdown test on single-arch model.The construction of the multiple-arch tunnel is deeply related to the form of center partition, the tunnel's section and excavation method etc. The change regularities of stress field caused by excavation are studied by 4 multiple-arch unlined tunnel model tests. The difference in lining for various multiple-arch sections is analyzed and the mechanics characteristics of center partition is discussed. Then, a reasonable construction method for multiple-arch tunnel and a better section are put forward. The zone between vault and center partition of multiple-arch tunnel being seriously loosen is revealed and the loosen range comes to 2 diameters. The failure feature of multiple-arch tunnel within cracked surrounding rocks is get and a conclusion that the weak location is the crown and the center partition is drawn.The change regularities of lining pressure and the failure process of surroundingrocks in permeation which a special sand is used as model materials are successfully simulated. The basic theory is established for the study of same type and the scientific basis for the tunnel prop design in saturation rock is provided.On the basis of model test, a better construction method under pre-prop for the surrounding rock I , II , III, named whole section excavation with heading in moderate degree and that with center heading and center partition first, then with two sides heading, is put forward. The characteristics of stress and displacement in tunnel surrounding rocks are studied. The change feature of the stress in surrounding rocks and the variations of stress and the displacement of prop structure in different excavation step are analyzed with 3 dimensional FEM. Finally, the construction method is proved to be reasonable and scientific.