Study On Mechanical Behavior And Construction Technology Of Shallow Buried And Large-span Tunnel With Soft Base Undercrossing Expressway

Urban tunnel construction is continuously faced with difficulties from complex environment, such as shallow buried depth, large span, soft surrounding rock, watery strata, undercrossing buildings or structures, which easily cause engineering disasters including collapse, intrusion into clearance gage of support, excessive ground settlement, inclination and mechanical failure of buildings or structures. Combining with the project of Hongmianlu tunnel undercrossing Jihe expressway, by methods of literature investigation, numerical calculation, theoretical analysis, laboratory test and field monitoring measurement, this dissertation systematically studies key problems as construction methods and technical measures of shallow buried tunnel undercrossing expressway with super-long distance. The main research contents and conclusions are as follows:(1) The optimized double side drift method and traditional method are compared by numerical calculation. It is pointed out that large advance displacement and large extrusion displacement are important reasons of serious deformation in tunnel construction. The deformation control effect of tunnel face reinforcement is analyzed according to both results of numerical calculation and measurement. Based on the analysis of aspects from the construction cycle length with corresoponding requirements of traffic organization and displacement control, it is found after analysis that the optimized double side drift method is of great superiority in the construction of Hongmianlu tunnel undercrossing Jihe expressway.(2) Based on the elastic theory of Winkler, mechanical models and corresponding calculation method of vertical-load-bearing role of pipe-shed advance support and foot-locking bolt are put forward respectively.And on this basis, a calculation model and corresponding calculation method of foundation load at the foot of tunnel with partial excavation method are put forward,and are applied in the project relied on later. The calculation results show that there exist the problem of insufficient foundation bearing capacity and that it may lead to great entire sinking of tunnel.The reasons and its control measures of arch-foot sinking are systematicly summarized.(3) According to the actual geological conditions of the project relied on, the strength characteristics of soft soil with different water content in rich water strata is studied by laboratory test.And based on results of the laboratory test, the influence of saturation degree on the bearing capacity of soft soil is discussed.Calculation and analysis of the effects of ground water content on tunnel deformation and construction security is conducted. And on this basis, specific measures are proposed to deal with the groundwater.(4) By using the method of field monitoring measurement, the surface settlement and the tunnel stress are traced and feedbacked during constrution with the optimized double side drift method. And thus security and reliability of the tunnel method and measures is known timely. Measurement results show that the optimized double side drift method with series of proposed technical measures can ensure the safety of Hongmianlu tunnel to undercross Jihe expressway.