Abstract Based on the structure feature and behavior subject to disturbance,a structural model was established for complicated surrounding rock in tunnel engineering. The model specified the structure stability and calculation method of load effect,and realized the coupling of the load-structure model with the stratum-structure model. After excavation,the initial stress is released and the pressure is transferred,usually in a form of pressure arch. The failure of surrounding rock shows a progressive character. The concept of deep buried and shallow buried surrounding rock was put forward according to the stability. The different structure features among rock groups resulted in the discontinuous and phase-dependent character of the failure of deep buried surrounding rock. Surrounding rock in the same group move synchronously and its simultaneous failure gives rise to the outside rock formation to sustain the stability of the exterior rock,that is,a composite arch structure varied with time and space. Each deep buried rock group consists of structure layer and load layer. For rocks in the structure layer,they usually own larger thickness,strength and stiffness,so as to maintain the stability of the rocks in this group. In contrast,rocks with small thickness,strength and stiffness are classified as load layer,exerting on the structure layer. The instability mechanism of structure layer was revealed and the corresponding criterion was presented. The load effect of complicated surrounding rock in tunnel engineering is composed of the given pressure of shallow buried surrounding rock and deformation pressure of the deep buried surrounding rock. The former depends on the scope and character of the shallow buried surrounding rock and the latter depends on the controlled state and stiffness of theforce transfer layer.
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