Study On Load And Secondary Lining Internal Force Characteristics Of Highway Tunnel In Small-Scal Thin Coal Ceam Mined-Out Area

Coal mined-out area is generated after the coal mining activity in coal-bearing region. It is a typical unstable layer and usually has the property of high porosity, big dispersion and poor stability. In the past, avoidance routing measures is always taken to deal with the coal mined-out area during the traffic tunnel route selection. However, with the traffic network planning becoming more and more dense, the cost of avoidance routing on coal mined-out area will be higher and higher. As a result, more and more tunnels will be constructed in coal mined-out area. Tunnel construction will affect the original balance of coal mined-out area and lead to stress redistribution, which can increase the risk of excavation and change the mechanical characteristics of support system. To clarify this problem, bearing capacity and structure shape of thin coal mined-out area are simulated using numerical analysis software of PFC and indoor scaled model test was carried out based on Tianpingzhai highway tunnel. The main research results are as below:1. Adaptability of the software PFC in coal mined-out area was analyzed according to the formation mechanism of coal mined-out area and characteristics of PFC.2. In this research, given that the three-dimensional relationship between the highway tunnel and coal mined-out area is equivalent to two-dimensional relationship, the numerical analysis model was built using PFC. Influence law of tunnel lining loads affected by the primary support stiffness, the microscopic failure characteristics of surrounding rocks and distribution law of tunnel lining load under overlying or underlying coal mined-out area were acquired. Suitable analysis of load-structure design method in coal mined-out area was conducted on the basis of numerical results.3. According to the principle of plane strain and scaled model test, the geometric scale CL=20 and gravity scale Cγ=1 are selected as the foundational similarity ratio to determine the rest similarity ratios of parameters. Then the thin coal seam mined-out area and highway tunnel lining were simulated by particular model materials. Characteristics of deformation, internal force and failure of secondary lining were monitored in the test. And the test results can provide reference to lining safety and health during tunnel operation in coal mined-out area.