| With the vigorous rise of urban rail transit construction such as subways,various engineering problems have also emerged one after another.Under the complex geological conditions in my country,karst problems have become one of the most common geological disasters in the construction of subway projects.Karst areas are prone to form karst caves and crevices through the long-term action of underground or surface water,which seriously affects construction safety and construction process.In underground construction projects in karst areas,researchers have mainly carried out more research on the impact of karst caves,while research on karst and even deep fissures is rare,especially in coastal areas under water-rich conditions.Based on Dalian Metro Line 5,this paper uses finite element simulation method to explore the influence of water-filled fissures in karst areas on shield tunnel excavation.It has certain reference significance for later scholars on the impact of water-filled fissures.The main research is The content and results are as follows:(1)The characteristics of karst development are studied according to the geological conditions in coastal areas and along Line 5,and the karst development conditions,influencing factors,grade division and related theories of soil mechanics are summarized.Further,according to the main stages of excavation,shield tail grouting,shield tail disengagement and soil consolidation and settlement that affect the stability of the surrounding rock during the shield machine excavation process,it will be combined with the earth pressure balance shield method during the construction process.The actual construction procedures were compared,and a three-dimensional finite element simulation model of the tunneling process of the shield machine was established,which laid the foundation for the subsequent numerical analysis of the effects of water-filled fissures.(2)Analyze the geological conditions along Dalian Metro Line 5,reasonably select the excavation parameters,fracture shape and size,and establish a three-dimensional finite element simulation model for excavation.Under the conditions of different azimuths and different lengths of cracks,the influence of the tunnel stress field and displacement field at different excavation steps during the excavation process is studied.The results show that as the length of the crack increases,the average stress and displacement of each monitoring point will increase,and the maximum stress points are all transferred from the initial arch toe monitoring position to the arch waist at the final step;with the size of the crack Increased damage to the integrity of the surrounding rock will increase the lateral displacement of the monitoring point of the arch waist.(3)The finite element simulation analysis of the influence of the cavern on the stress and displacement field of the surrounding rock during the shield tunneling process under the water-filled condition was carried out,and the simulation results were compared with the simulation results under the water-filled crack condition.Generally speaking,compared with the case of caves,the maximum stress generated by the surrounding rock in the presence of fissures is greater;and the integrity of the surrounding rock is damaged by the water-filled caves,which is caused during shield excavation.The displacement is larger.Among them,the vertical displacement difference is small,while the lateral displacement difference is more obvious,showing the convergence of the original position to the direction of the tunnel center. |
