| The existence of karst caves will have varying degrees of influence on the tunneling,tunnel structure and future operation of tunnels under construction.The influence of karst caves on tunnel lining can be said to be determined by three aspects,namely,karst caves,tunnels and surrounding rocks.At the same time,the two of them influence each other.Each quantity of karst cave,tunnel and surrounding rock is calibrated by multiple physical quantities.In this paper,the surrounding rock conditions and the lining structure parameters of metro tunnel are set unchanged.Only from the development and distribution of karst caves,the filling degree,span,diameter of karst caves,and the location and distance from the tunnel are taken as variables.Through numerical simulation and theoretical analysis,the influence of karst caves on the internal force and deformation of circular metro tunnel lining structure under limestone geological conditions is studied.It provides theoretical and technical support for safe tunnel construction and operation.The main research contents and achievements are as follows:Research on the types of karst caves and their relationship with the location of tunnels: Based on the common karst spatial distribution patterns and characteristics encountered in the construction of Jinan Metro Line 4,the development degree of karst and its relationship with the location of tunnels are analyzed.According to the different influence degree of karst cave on tunnel lining,the treatment of karst cave is given.The close tunnel cave with large span,large diameter and low filling degree is a serious threat to the safety of tunnel lining structure and should be dealt with in time.The karst cave within 2 meters of the tunnel body has great influence on the force and deformation of the tunnel lining structure,which must be dealt with.The cave within 2-8 meters has a great impact on the lining structure of the tunnel,so it can be treated as appropriate.The karst cave 8 meters away has little influence on the lining structure of the tunnel,so it can not be treated under normal circumstances.Karst caves mainly affect the lining parts of adjacent tunnels.Different karst caves with different development and distribution patterns have different impacts on the lining structure of subway tunnels.The larger the volume of the cave and the closer the distance to the tunnel,the greater the influence on the tunnel lining.The increase of the span and diameter of the unfilled cave directly increases the volume of the cave,which has a great influence on the tunnel lining.The increase of the filling degree of karst cave not only reduces the volume of karst cave,but also restricts the development of karst gap to a certain extent,delays the failure of karst cave roof,restrains the loss of geotechnical mass between karst cave and tunnel lining,and maintains the relative stability of karst cave and tunnel.When the tunnel is completely filled,the deformation and force of the tunnel lining are close to the condition of no cave,which reflects the importance and necessity of complete filling and sufficient grouting when treating the cave disease. |
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