Analysis Control Norm Of The Deformation And Stability For Large Section Tunnel In Loess

In recent years, in order to narrow the gap between the central and western development, western transportation system are constructing rapidly. Tunnel as a building that can make the line more smooth and straight is frequently used in western region traffic system. Because loess stratum are widely distributed in west of China, and the train speed becomes faster which lead to tunnel excavation sectional area increase. These factors make the topic of a large section tunnel through loess stratum.Taking Wang Jiagou tunnel of Bao Lan passenger dedicated as the project background, summarize the engineering properties of high water content loess and advances in the field of large section loess tunnel excavation by studying literature; Make tests for undisturbed soil samples of Wang Jiagou tunnel in laboratory to get the main physical and mechanical parameters and comparatively analyze the engineering properties for loess with different water content. The deformation control reference of Wang Jiagou tunnel whose depth is 50 meres is analyzed based on the Catastrophe theory by finite element software, the stability of tunnel is analyzed after tunnel bench excavation at the same time. In order to clearly study the force conditions of the supporting system after tunnel excavation, monitoring equipments were installed in Wang Jiagou tunnel DK983+892 section to collect the data of force condition of tunnel supporting system, the data is used to analyze the regularity of the tunnel stress variation and the distribution of cross section. On the basis of analyszing tunnel deformation and stress comprehensively judge the tunnel stability; Using MIDAS finite element analysis simulation software study the characteristics of supporting system stress when tunnel is excavated and tunnel cross valleys and craters. The Laws and conclusions that are summarized by studying the deformation control reference and tunnel stability of large section loess tunnel are as follows:(1) The engineering properties of loess is very different when loess moisture content is changed after reviewing literatures and laboratory analysis, With the increase of moisture content of loess, friction angle and cohesion are sharply reduced.(2) Based on catastrophe theory, the deformation control reference of large section loess tunnel is established by finite element software, when tunnel depth is 50 meres. It is economic and efficient to use finite element software to establish deformation control reference for different tunnel section by various excavation methods.(3) Research force characteristics and section distribution form of tunnel support system by field tests and numerical simulation results, It found that supporting system bear great compressive stress on the upper part of maximum cross-tunnel and tensile stress near sidewall; It is a comprehensive and effective method to determine the stability of the tunnel from its deformation and stress.(4) The large section loess tunnel stability is researched by numerical simulation when it through valleys and craters, the study show that the impact of valley for tunnel excavation which can be ignored when the least tunnel depth greater than two diameters and craters is one diameter.