| A great threat is imposed on the tunnel construction and operation security by geological disasters such as Karst tunnel cave collapse and water burst,which has drew more attention of researchers from domestic and abroad.It is of great significance to study the characteristics and laws of karst development in karst area,develop appropriate cave prediction scheme,analyze the influence of cave on the deformation characteristics of tunnel surrounding rock,and make reasonable cave treatment solution.Karst is well developed in Qiyueshan tunnel area.Some high-risky projects such as Yiwan railway and Shanghai-chengdu tunnel have been carried out.During the construction,more than 100 water burst accidents happened and more than 10 caves were discovered.Many water disasters occurred during the construction of Liwan high-speed tunnel which is connected with Qiyueshan tunnel.More than 10 caves with the diameter larger than 10 meters were found within 100 meters in the tunnel.GK3+210～GK3+272 has a length of more than 100 meters,which imposes a great difficulty to the tunnel construction.Therefore,this paper aims to study the develop mechanism of cave based on the statistic data of four Qiyueshan tunnels,predict the potential cave using displacement measurement method,analyze the influence of single cave and multi cave on the deformation of the tunnel surrounding rock,and develop technical treatment system for the cave under different distribution conditions.The research results can provide important theoretical basis and technical guidance for the construction of tunnels with similar karst caves.The main contents of this paper are as follows:(1)Typical engineering cases of caves were collected and the control factors as well as the occurrence rules of cave development were summarized.The advanced geological forecasting technology of tunnel bad geological body recognition was studied.Explore the control factors,characteristics and classification characteristics of karst development in Qiyueshan tunnel area based on the data of Qiyueshan tunnel and Yiwan railway tunnel.The methods used include field geological survey,construction site investigation and karst water tracing test.(2)Based on numerical simulation,the displacement characteristics of the surrounding rock under different construction steps were studied for single caves with different shapes,different sizes and different distances.The effects of single concealed caves on the displacement characteristics of the surrounding rock were studied.The mechanism of cave instability is explored,which provides theoretical basis for the concealment cave prediction method based on displacement monitoring and the treatment of cave.(3)Based on numerical simulation,the influences of the vertical cave combination,the horizontal cave combination and the longitudinal cave combination on the displacement characteristics of the tunnel were discussed,which can provide theoretical basis for cave prediction and management.(4)Based on field investigation and the study of the influence of the hidden cave on the displacement of the tunnel surrounding rock,a new method of concealed cave prediction was proposed,which is based on the monitoring method 6f concealed cave.Numerical simulation is used to validate the feasibility of the proposed method for predicting concealed caves.The operation steps of the method are described in detail,which provides a new idea for the prediction of tunnel hidden cave.(5)The treatment technology for different cavern cave in different parts of the tunnel construction process was summarized.The deformation characteristics and failure mechanism of the surrounding rock were analyzed based on the example of the cave project in the construction process of Qiyueshan tunnel,which provides important basis for cave treatment and tunnel support. |
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