| In recent years, with rapid and stable development of China’s economy, increasing demand for mineral resources lead to a large number of mineral resources exploitation, resulting in a wide range of mined-out area. At the same time, a large number of construction and the increasing of network density of high-speed railway make it inevitable that highway goes through the mined-out area. The multi-arch tunnel is widely used for its unique advantages, which is often at shallow bias. Due to its poor stability of surrounding rock, the engineering mechanics properties of the complex, the tunnel construction waterproof and drainage management is difficult, spatial variation of mined-out area will make the multi-arch tunnel construction mechanical behavior more complex. With the engineering background of Mount Wofo shallow bias multi-arch tunnel through mined-out area, based on the initial geological exploration engineering data, field-monitoring measurement, geological radar detection results and finite element analysis as the main means, this paper explores the stability of shallow bias multi-arch tunnel in mined-out area. The main results are as follows:Monitoring measurement is carried in Mount Wofo shallow bias multi-arch tunnel. The monitoring results find that: crack development, surrounding rock broken, several empty of mined-out area exposed. Tunnel deformation greatly influenced by shallow the fracture zone and empty of mined-out area.Ground penetrating radar is used to prove distribution law of mined-out area under mid-partition of Mount Wofo tunnel, such as the number, size, buried depth, spatial location of mined-out area. Detection results show that: mined-out area are mainly distributed in the tunnel below 0~16m and length is 4~12m。According to the initial geological exploration data and mined-out area ground penetrating radar detection results, with the finite element method, Mount Wofo multi-arch tunnel the three dimensional numerical model is built which pass through complex mined-out area. At the same time, this paper analyses the influence of spatial distribution on initial ground stress field and displacement field, which reveals the influence of deformation in mined-out area.Based on 3d model of the shallow buried bias multi-arch tunnel, whole construction process is simulated. From surrounding rock, mid-partition and primary support, the influence of mined-out area on shallow and unsymmetrical loaded double-arch tunnel is analyzed. Research shows that: within the scope of 6m for mined-out area at the bottom of the tunnel, it is strong impact area, which requires corresponding governance, besides the 10 m, it is no affected zone, which is no need to manage; between 6 ~ 10 metres, it is weakly affected zone, which is need to strengthen monitoring.A simplified 2d model is established to research influence of different mined-out area spatial location and size on stability of shallow and unsymmetrical loaded double-arch tunnel. Research shows that when the mined-out area is under shallow buried tunnel, it will have less effect on the stability of tunnel. When Mined-out area is on the side or below of deep buried tunnel, it has greater influence on the stability of tunnel, and it will increase the bias effect. With the increase of mined-out area size and the decrease of distance between tunnel, the influence of Mined-out area on stability of tunnel will gradually increase.Mined-out area treatment solutions are summarized. Preliminary evaluation on the governance solution and management effect to shallow and unsymmetrical loaded double-arch tunnel in Mount Wofo are carried. |
