Abstract:

Zaosheng No.3 Tunnel on YinchuanXi′an Highspeed Railway, the first tunnel crossing paleosol stratum in China, is located in Ningxian County, Gansu Province. In order to study the pressure distribution of surrounding rock and the stress and deformation characteristics of supporting structure when tunnel crossing paleosol stratum, the pressure box, surface strain gauge and steel bar stress gauge are installed at a same mileage of tunnel to monitor the pressure of surrounding rock and the stress and deformation of primary support for a long time. And then the frequency obtained is converted to force or strain, and finally the data are analyzed. The results show that: (1) For the threebench sevenstep excavation method, the pressure of the surrounding rock has experienced three stages, i.e. rapid change, slow change and steady change; by using the threebench sevenstep excavation method, the pressure of the surrounding rock excavated firstly is obviously larger than that at the side excavated lately at a same mileage. (2) The steel arch presents a threedimensional stress state, the axis force of the two adjacent arches is mainly subjected to pressure, and the degree of integration of the supporting structure and the cooperation with the concrete directly affect the axial force. (3) The maximum strain of the arch feet is mainly concentrated on the bottom of the top heading and the bottom of the inverted arch.

Key words: large crosssection tunnel, palesol stratum, threebench sevenstep excavation method, surrounding rock pressure, supporting structure, threedimensional stress mode of arch frame