Research On Construction Control And Disturbance Of Surrounding Rocks During Large-span & Shallow Tunneling In Rugged Terrains Area

Tunnel engineering often face disadvantage geological and topographic conditions because of its environment of construction is complicated. Although the control of surrounding rock large deformation has accumulated massive experience, there are still many collapse accident in the tunnel construction. It indicates that tunnel construction exist some expects unsafe yet. So, it is still very important to research the construction control and disturbance of surrounding rocks during large-span and shallow tunneling in some special area.The paper rely on the CongKeng tunnel project of NanLong railway. It combined the strata displacement related with the data of field test, mainly research the strata displacement and characteristics related when the tunnel is constructing underneath shallow and downslope area. At the same time, through the numerical simulation calculation for CongKeng tunnel, it intend to verify the correctness of the law when the tunnel is constructing underneath shallow and rugged terrains area and the deformation mechanism. The details of this paper narrate verbose as follows:1. Based on theoretical formula of Peck and Attewell, the paper analysis the data of field test. It indicates that the disturbance of surrounding rock particularly related to the construction procedure of tunnel. And it presents the regulation that sharp deformation to slow deformation to tend to be stable for the deformation of the surrounding rock on the whole.2. The paper also compare the data of field test with numerical simulation calculation.The deformation of the surrounding rock will be increased abnormally when the excavation of tunnel underneath shallow and downslope area. And it show that “bulge” on the vertical distribution of the cumulative settlement. Meanwhile, numerical simulation calculation for CongKeng tunnel show the same conclusion as the field test. Therefore, the above analysis indicate that the overlying strata of tunnel affected by the shallow and downslope area.3. Large-span tunnel will occur the larger vertical displacement and horizontal displacement easily when it excavate on v class surrounding rock by analysis the surrounding rock deformation and construction control of large-span tunnel. In the meantime, excavation of tunnel will occur concentration of stress on the vault, the bottom and springing of the tunnel. So the paper suggest that we should take some safety measures to control the deformation of the tunnel after the tunnel excavation in time.4. Tunnel excavation lead plastic range of the tunnel overlying strata fasten on the middle downslope area. So it influenced by the extrusion of the latter soil, and middle downslope area also create concentration of stress because of the unloading effect of tunnel excavation at the same time. Therefore, the middle downslope area will be in unsteady state to cause collapse accident. And due to a shallow depth, tunnel excavation can expand the disturbance area of surrounding rock. The soil will be damaged eventually when the shear strength played out is greater than actual shear strength.