An Analysis Of Mechanical Characteristics And Stability On Swelling Loess Tunnel Surrounding Rocks Under Rainfall Infiltration

Swelling loess is a complicated geological mass, which is harmfulness to constructional engineering. Swelling loess is widely distributed in China, especially in the Midwest of our country. In recent years, with the development of the construction of roads and railways in the Midwest, more and more tunnels were inevitably constructed through swelling loess strata. Swelling loess has lot of adverse engineering characteristics, such as the swell-shrink, crack, and over-consolidated, which could cause the large deformation, collapse, and et al of tunnel. In the light of an under construction swelling loess tunnel in Shanxi province whose primary support had badly deformed and cracked and finally evolved into collapse, due to the swelling stress and the declined strength of the surrounding rocks induce by rainfall infiltration, this paper aimed at analyzing the adverse impact of the swelling loess tunnel surrounding rocks under the circumstance of rainfall infiltration, and uncovered the failure law of the surrounding rocks of swelling loess tunnel and the mechanical characteristics of the primary support liner. The main contents are as follows:(1) Obtained the basic mechanical properties, mineral component and swelling characteristics of the swelling loess sample from laboratory test. The soil’s matric suction was measured by filter paper method, and SWCC curve was fitted with these test data. With the Direct Shear Test of reformed swelling loess of different water contents, strength change laws were acquired, which provide the basis for numerical simulation.(2) In order to simulate the process of unsaturated seepage during rainfall infiltration, a program was wrote with FISH language and embed into the software of FLAC3D. This program can simulate the swelling of the soil when water content increased, and can also deal with the problem that strength of surrounding rock change with soil water content.(3) Use the method above to simulate an under construction swell loess tunnel which was collapse during rainfall infiltration, then analysis the mechanical characteristics of swelling loess surrounding rocks and support structure.(4) Monitoring test in tunnel construction site. On one hand, in order to uncover the Stress Characteristics of some sections, a group of pressure cells and strain gauges were installed to monitor the surrounding rocks pressure and Steel arch stress respectively. On the other hand a series of deformation monitoring was carried out in the Vault, Sidewall, and ground surface. After a comprehensive analysis of monitoring data and the failure characteristics of tunnel, then compare with the results of numerical test, a further summary was made about the mechanical characteristics and stability of swelling of the loess tunnel surrounding rocks under the circumstance of rainfall infiltration...