Analysis Of Dynamic Response And Stability Characteristic Mechanism Of Subway Tunneling In Saturated Loess

With the development of our country infrastructural facilities in western area includes conservation, transportation, city construction and so on, there are more and more shallow tunnel projects in the loess area. For example, the Xi'an subway tunnel in the freshly piled up weak loess, tuunel of the Yellow River Cross Midline Engineering of South-to-North Water Diversion Project, highway tunnels in the Northwest China Area and so on. When receives the vibration load function, these saturated weak loess is sensitive to vibrate, its soil structure encounter the perturbation to soften, causes the loess to the hydraulic pore pressure rise, the effective stress to reduce, and urges the soil to the distortion rise, the intensity to reduce, even has the liquefied destruction. Underground structure in the saturated liquefied soil layer uplift as a result of excess static pore-water, causes the serious destruction to the underground structure. But recently, study on the destruction to the underground structure by liquefaction domestic and foreign is few.This paper is related to the problem of dynamic response and stability characteristic of subway tunneling in saturated loess, based on the numerical simulation of the process excavated, under different rock stress conditions, the equivalent viscoelasticity dynamic response and dynamic pore pressure solution, and the elasto-plastic solution under uplift function solve step by step calculation, Under the different stress release rate, the different earthquake acceleration, the different burying depth, the different hole diameter change condition, this paper research on the tunnel hole differential pressure, pore pressure field distribution, liquefaction area as well as uplift displacement change. For a different supporting time hole into the tunnel excavation, with the initial stress in the surrounding rock in the tunnel and initial stress reverse impose the same release the equivalent of the simulation node, consider themselves lining load conditions in a hole under the formation of linear elastic numerical solution of the excavation process of the release of displacement and stress of the relationship between static and dynamic stress on the development and distribution of pore pressure of the impact and displacement under the proposed rate changes in the stress analysis of surrounding rock stability Methods. Accordingly to saturated loess rock cavern may lead to the existence of floating liquefied displacement development issues, raised rock static stress field identification, the equivalent viscoelastic dynamic response analysis based on dynamic pore pressure field calculation, dynamic pore pressure from the tunnel under floating Elasto-plastic deformation of the surrounding rock in the tunnel under the dynamic role of floating displacement method.The analysis indicated that with the increasing of the stress release rate, the hole arch displacement gradually decrease. When the stress release rate is bigger than a value, the hole arch displacement is increase rapidly, this is a marginal value (the biggest permission release rate); Under the identical hole diameter condition, the burying depth is bigger, the biggest permission release rate is bigger; Under the identical burying depth condition, the hole diameter is bigger, the biggest permission release rate is smaller. Under the identical stress release rate condition, with the increases of burying depth, the differential of dynamic pore-water pressure is bigger; With the increasing of hole diameter, the differential of dynamic pore-water pressure is increase. Under the identical burying depth and hole diameter condition, the biggest permission release rate is bigger, the differential of dynamic pore-water pressure between hole bottom and hole arch is bigger; The vibration acceleration is bigger, the differential of dynamic pore-water pressure between hole bottom and hole arch is bigger. These rules obtained the quantitative analysis in view of the saturated loess tunnel that has the actual guiding sense.Finally, based on the earth dynamics earthquake equivalent load, the dynamic pore-water pressure theory, the tunnel construction stress release rate estimation as well as the hole arches plastic deformation in the process of excavation. This article bring forward the uplift displacement numerical simulation analysis thought, and further promote the uplift displacement computational method of simplifications, convenience, the practicality.