The Effect Of Ground Fissure On The Stability Of Cavern Adjacent Rock In Xi'an

The ground fissure is one of the ground disaster in the geological disaster, it worsens the environment, reduces the environment quality, harms human and the biosphere development. The ground fissure has been found in many countries of the world, it happened more frequency and the disaster bigger year by year. The ground fissure not only creates each kind of project construction, such as city construction, lifeline project, transportation, farmland and water conservancy facilities, but also has caused a series of environment question. In recent years, the subway project has been mark out in Xi'an city. The excavation of underground hole is not a new topic, many Chinese and foreign scholars has studied it in many ways, but Xi'an's geological condition is special, such as ground fissure. So analyzing the degree of hazard on the ground fissure to underground hole, mastery its activity and development tendency, then forecasting the disasters to society. It is significance to the humanity life and property security, the city and countryside construction plan, and the development of consummation.The ground fissure is a kind of unceasing power supply for the geologic body, as a result of the ground fissure's activity, it produces deformation band and stress field, that cause the ground foundation occurring differential settlement, pull crack and staggered. It also creates the underground cavern, the roadbed and the pipeline distorted or sheared.This article takes the Xi'an subway basic geological situation as the projectbackground, analyzing relations between the ground fissure and the stability of cavern adjacent rock.Firstly, I use the software of ANSYS to analogue the excavation of cavern which passed through the ground fissure. Then contrasting the change situation of adjacent rock-support system between the ground fissure and non-ground fissure. When the cavern excavates to the ground fissure, the settlement and stress of adjacent rock have a larger scale increase. Because of the excavates of cavern, the settlement of adjacent rock is 30mm in non-ground fissure, and the settlement of adjacent rock is 38mm in ground fissure, it increases 8mm. In non-ground fissure the horizontal distortion is about 3mm on the side cavern, and in ground fissure the horizontal distortion is about 6~8mm, it increases 3~5mm. So the ground fissure has the decisive effect to the stability of adjacent rock.In the non-ground fissure, the tensile stress on the top of cavern is 0.139MPa, and in the ground fissure the tensile stress on the top of cavern is 0.765MPa. In the ground fissure the maximum principal stress is lower, but the stress gradually tends to stably far away the ground fissure. The shear stress is centralized in ground fissure.In view of the above fact that the destruction of the ground fissure to cavern is tensile failure on the top cavern and the shear failure on the side cavern, then it causes caving on the top of cavern and creeping on the side cavern. The ground fissure has the decisive effect to the stability of adjacent rock. Therefore, when excavates to the ground fissure we should complete the optimization construction steps, and adopts the reinforcement adjacent rock to guarantee construction security.Secondly, the ground fissure is regard as a plane of weakness, then analyzing the relations between ground fissure and the stability of adjacent rock throughtheory. On the basis of the elastic and plastic theory, we can gain the most adverse angle and position of the cutting and splitting area. Sample as the ground fissure of Xi'an city, the most adverse angle is about 51°. Thereout, we can ensure the position of the cutting and splitting area when the ground crack exists in different obliquity.