Study On The Tunnel Deformation And Mechanical Properties In Formations Combined With Karst And Water-rich Sandy Soil

The construction of underground rail transit in formations combined with karst and water-rich sandy soil may cause geological hazard, such as the collapse of cave roof, mud bursting and water inflowing, these phenomenon has become one of the most serious geological disasters.With the rapid development of rail transit, researches concerned with the safety of operating tunnel have been conducted by many scholars at home and abroad, but the karst caves that are too close to the tunnel and some are yet undiscovered(known as covered karst cave) haven’t been paying enough attention or systematically studied. Hence it is crucial to establish a model which could consider all kinds of possibilities and to predict the safe distance between the tunnel and karst caves.This paper is based on Line 9, Guangzhou Metro. The main contents of this article are as follows:(1)Analysis the geological and stratigraphic law of karst caves in thick sand layer area.The formation condition and failure mechanism of the collapsing caves along the metro line 9were summarized.(2)Base on the karst cave limit equilibrium theory, establish a karst cave equilibrium lost mechanical condition and its theoretical model, the stability of karst cave and its ultimate bearing capacity of the upper plate were analyzed.(3)Combining the theory with subway construction project, analyze the tunnel deformation, internal force changing and distribution law of formations combined with karst and water-rich sandy soil. Illustrated by the example of karst cave under the tunnel, analyze the safe distance and tunnel deformation pattern between the tunnel and karst cave.Meanwhile, establish a finite element model and analyze its reliability.(4) Consider the multi-factor effect, simulate the operating tunnel by using the final finite element model. Study the deformation properties and mechanical behavior of metro tunnel in formations combined with karst and water-rich sandy soil, analysis the safe distance betweenkarst caves and tunnel structure.(5) According to the calculation results, study the possible difficulties may occurred in the full operating period of tunnel in formations combined with karst and water-rich sandy soil and put forward the corresponding preventive measures, management measures and emergency measures.