Similar Model Test Study On Tunnel Surrounding Rock Stability In Xigeda Strata

Xigeda is a special half-diagenetic strata, its engineering properties generally between extremely soft rock and soil. Given its poor engineering properties, there are little railway and highway tunnels had been built in the Xigeda strata formerly. Therefore,the construction of the highway tunnel in Xigeda strata is a new subject, which is worthy to study and explore.Based on Huaping tunnel, one of li-Pan Highway tunnels, this papar used the laboratory similar model test as the primary method to research the tunnel surrounding rock stability in Xigeda strata.In this study, firstly by collecting relevant literature of Huaping tunnel and combined with geological survey, we had mastered the engineering geological background. Next, to acquire some physical and mechanical parameters of surrounding rock by laboratorying soil test. In the completion of the above preparation, we began the similar model test and got a series of research results.First, by simulating the Huaping tunnel excavation and while monitoring the strain situation of surrounding rock in all directions,it was concluded that the deformation law of tunnel surrounding rock after excavation.(1) After the tunnel excavation, there is the largest strain in vault of the tunnel, followed by arch feet, and arch waist is smaller compared to the first two.(2) With the increase of distance between surrounding rock and excavating surface,the strain amount of tunnel surrounding rock is logarithmic decrement.Tunnel surrounding rock deformation mainly occurs in the range of 1 times hole diameter,the deformation will become very small when the distance is more than two times the hole diameter.(3) Bolting support can effectively reduce the strain of the surrounding rock, but can not alter the characteristics of the surrounding rock stress redistribution after tunnel excavation.Second,using the contrast test to compare the difference of surrounding rock deformation between unlined and bolting state. It was concluded that bolt support could reduce the deformation of surrounding rock about 25%, which demonstrated that the pre-designed scheme of bolt support bolting could play a better supporting effect in the actual construction program.Third, according to the deformation laws of surrounding rock which had been concluded in the similar model test, this paper analyzed the validity and rationality of the related measures in the tunnel construction and give some appropriate proposals.Fourth, the numerical simulation method was adopted to analyzed the stress state and displacement of surrounding rock after Huaping tunnel excavation in this paper,and compared the conclusions of numerical simulation with similar model test.Finally, this paper compared the displacement monitoring data of Huaping tunnel with relevant data of the similar model test,and then authenticated the reliability and accuracy of the similar model test.The conclusions of this paper have a good reference value on design and construction for Huaping tunnel, as well as other tunnel in Xigeda strata.