Study on Share Rate of Support Structure for Super-Large Span Twin Tunnels with Small Interval

Abstract

Super-large span twin tunnels, which can relieve traffic burden and improve the efficiency of roads, have been rapidly popularized in urban construction. Hence, it is very important to master the share rate of support structure in this sort of tunnel correctly. In this paper, some field monitoring and numerical simulation work has been carried out in such a tunnel in Daling, China. The content of field monitoring consisted of the vault settlement, stress of the concrete, and the sum pressure. Firstly, the calculation formula of rock pressure in this kind of tunnel had been deduced, which was based on the theoretical sliding failure mode. Then, the calculated rock pressure was applied to the load structure model step by step with 10% intervals (10%, 20%, …). By comparing the monitoring and the simulation results on vault settlement, the share rate of the primary support was ensured to be 40%. Similarly, by comparing the result on safety factors, the share rate of the secondary lining was obtained (40%). The remained load was born mainly by the surrounding rock itself and the advanced support. Finally, the reliability of the results were verified by the sum pressure. This paper can provide reference for the effective design of support structure in super-large span twin tunnels.