Study On Underground Cutting Technique With Shallow Overburden And Environmental Effect Of City Underpass

Construction of the underpass is an effective measure to ease city traffic congestion, enhance pedestrian safety and improve the efficiency of the city. The influence of the underpass construction to the surrounding environment is inevitable, even may affect the ground buildings and the normal use of the underground pipeline. Therefore, it is significant to select an appropriate construction method to reduce the environmental effects. This paper, on the basis of the results of previous studies, has done a systematic study on the actual situation of the city underpass construction technique and its environmental effects. It runs as follows.1. Based on two-parameter Pasternak model, a calculation model and differential governing equation which reflects the work of pipe roof mechanism has been set up and solved.2. Based on M. M. Protodyakonov Equilibrium Arch Theory and Terzaghi Loose medium Theory, a calculating method of digging length has been given when full-face tunnel excavation is adopted in shallow tunnel construction in homogenized soil. Then, the methods have been applied to usual excavation method (e.g. step method, CRD method) and the construction in layered soil. At last, the methods have been proved to be practical in design and construction according to application in an example.3. A detailed analysis of the numerical simulation of the underpass, 4m depth in silty sand soil and soft soil, construction technology has been conducted. Then, numerical analysis of digging length and division excavation length has been carried out according to different digging length (2～7m). On the premise of the safety of underpass and surrounding environments, reasonable proposals have been given to underpass construction technology when it is done at different depths of silty sand soil and soft soil (including excavation methods, digging length, division excavation length, steel grating spacing, the length of support etc.).4. Through numerical simulation, detailed study has been done to the pore pressure changes and changes in surface subsidence caused by single-well and multi-well precipitation in homogeneous soil. On the basis of the results, a precipitation model of the underpass construction in gouache-rich sand soil has been made. Pore pressure changes and changes in surface subsidence caused by different precipitation construction technology have been studied to point out that dynamical precipitation is an appropriate precipitation method.5. Numerical simulation and analysis on the impact of the different soil, construction technique and depth to surface subsidence have been done. On the basis of research results influencing factors and control measures have been summarized.6. Numerical simulation and analysis on the impact of the underpass construction to underground pipeline under different conditions (including different material, depth and space) has been done.7. Through the study of an actual subject and the comparison between the numerical simulation results and actual data, the construction methods proposed by this paper have been proved and can be applied to practical engineering.