Study On Key Issues Of Design And Construction Of Underground Pedestrian Crossing

Underpass is an effective way to reduce city traffic congestion, to enhance pedestrian safety and to improve the running efficiency of city. The influence of the underpass construction on the surrounding environment is inevitable, which may affect the neighboring buildings and the normal use of the infrastructures. Therefore, it is significant to select an appropriate construction method to reduce the environmental influence. On the basis of data collection and case investigation, a systematic study has been carried out on the city underpass construction techniques and the environmental impact.Firstly, for the case of Mingyue Road 2# underpass in Guangzhou, China, according to the general calculation method recommended by the national code, the internal forces and deformation of the lining structure were calculated by the aid of the software of SAP2000. The calculation section and the applied forces were determined according to the code. Secondly, finite-difference element software FLAC^3D was applied to simulate different construction methods to see which one could guarantee the crossing's stability and strictly control the ground subsidence. The main contents are as follows.(1) By conventional method aided by SAP2000 calculation, internal forces of the shallow-buried underpass in aqueous soil were computed. By comparing the internal forces with the bearing capacities, it was concluded that it is the moment which controls the design of the lining section.(2) According to the case of Mingyue-Road Two underground pedestrian in Gangzhou, China, the comprehensive construction techniques of shallow-buried underground tunneling in silt stratum were introduced, such as pipe pre-support technique, grouting technique for tunnel face, short-distance excavation and strong supporting technique. The surface vertical dewatering and strata dewatering technique of combining long pipes with short pipes, were also talked about. The finite-difference software FLAC^3D was used to simulate the construction effects. The calculating results suggest that the tunnel keeps stable all along in construction process. The pipe pre-support technique is practical and feasible in underground tunneling with shallow overburden in aqueous silt stratum since the ground safety and subsidence were well controlled. The research herein could offer a reference to similar projects in future.(3) A detailed numerical simulation of a 4m-depth buried underpass in soft soil was conducted to study the influence of construction technology. Different digging lengths and the division lengths of the excavation had been simulated. On the premise of the safety of underpass and surrounding environment, reasonable proposals have been given to underpass construction technology when it is built at different depths of soft soil.