Research Into Effect Of Moisture Content On Stability Of Surrounding Rock With Gravelly Soil In Large-span Tunnel

With rapid development of transportation in China, highway tunnel constructionhas already entered a new developing age. More and more mountain tunnels are built.Environment and geological conditions on JinPenwan large-span mountain tunnelwhich is located in JiHu highway project are complexity, and surrounding rock mainlyis consisted of gravelly soil. Gravelly soil has properties of loose and soft under water,which brings on huge risks to construction of tunnel. Therefore, it is necessary toanalyze stability of surrounding rock and reasonable selection of secondary supporingtime in different moisture contents. In this paper, based on field monitoring, experimentand numerical simulation, the main researches are followed as:(1) Comparing and analyzing the field monitoring of vault settlement, surroundingrock pressure and internal stress of initial steel support with water and without water, itis observed that water brings great influence on stability of surrounding rock.(2) Based on gravelly soil from JinPenwan tunnel, effects of moisture contents andcoarse-grain contents on mechanical properties are investigated by the large-scale directshear test.(3) Excavation and support of tunnel with different moisture content arenumerically simulated by ANSYS finite element software. Effects of different moisturecontent on surrounding rock stability are researched by analyzing peripheraldisplacement of surround rock, pressure of surrounding rock and stress of initial steelsupport.(4) In different moisture contents, equivalent node forces of surrounding rock after excavation of tunnel are concluded by ANSYS finite element software. Rationality ofsupporting time for tunnel is simulated by controlling the proportion of equivalent nodeforces. Surrounding rock pressure, deformation and mechanical properties of supportingstructure with different moisture content are investigated, and the optimum supportingtime of secondary lining is presented.(5) Based on content of water of real surrounding rock, supporing time ofsecondary lining is optimized according to the three dimensional numerical results byANSYS finite element software. Comparing simulation with monitoring results,rationality of model is verified. This conclusion will provide a certain reference forconstruction of similar tunnel with gravelly soil.