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Abstract To investigate the progressive failure progress of rock mass with increase of buried depth in super section tunnel，a 3D geomechanical model test system with homogeneous gradient loading and similar material of weak broken surrounding rock and support system were developed. Then the 3D model test was carried out which showed the progressive failure progress of weak broken surrounding rock of entire section method and bench method. Firstly，the weak broken surrounding rock in a range of 200–1 020 m in depth was taken as an example. The strain softening behavior of weak broken surrounding rock and shotcrete can be simulated by different proportion mixtures of iron powder，quartz sand，barite powder and rosin alcohol solutions. Polytef sticks can be used to simulate the bolts. Besides，combining the micro-devices of excavation and construction supporting the construction progress of entire section method and bench method can be well simulated by the 3D model. In addition，the changing information of stresses，displacements and loads in the scope of entire times of the tunnel diameter(0–3 times) can be monitored by fiber grating sensors，resistance strain gauge，multipoint extensometer and micro pressure cells. Secondly，an overloading test was carried out after the end of excavation. The loading gradient was 50 m on the direction of the burial depth until the significant failure characteristics occurred in the no supporting sections. Then the loading gradient was changed to 20 m until the initial shotcrete damaged in large areas. The test results show：(1) The failure zones of rock masses expand with the increase of the burial depth. The no supporting sections fail earliest. Then the failure zones extend to the supporting sections. And the final areas of failure zones decrease gradually. (2) The failure zones of rock masses of no supporting sections and the liner failure zones of supporting sections mainly focus on the crown which is the load sources of the liner failure and the collapse of the surrounding rock. There also exist failure zones on the side walls. The degree of damage increases from the upper part of the side wall to the skewback. (3) The growth rate of displacements in supporting sections is smaller than that in no supporting sections with the increase of burial depth. However，the growth rate of stresses and loads are just opposite. The supporting structures burden the loads obviously. (4) The failure depth of surrounding rocks increase continually in the overloading test. The dynamic pressure arching phenomenon occurs in the scope of crown. Hence，the top reinforcement theory is feasible in theory. The research methods and results will instruct similar engineering.
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Received: 27 August 2011
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2012, Vol. 31 
