| In order to satisfy people’s demand for traveling,it is becoming more and more common to build tunnels in karst development areas.The influence of hidden karst caves on tunnels has also become an important factor affecting the safety of tunnel construction.Taking the separated tunnel constructed in karst area as the research object,this paper analyses the influence of the relative position of karst cave and tunnel on the stress and deformation of separated tunnel when the ratio of horizontal stress to vertical stress is greater than 3,and reasonably sets the stress and location of karst cave in surrounding rock,and studies the influence of the sectional shape of separated tunnel on the stress and deformation of surrounding rock in this case.After collecting the engineering information and establishing the physical and mechanical parameters needed to establish the model,the physical and mechanical parameters of the model are set up reasonably,and a numerical model is set up on this basis.The numerical model is simulated to analyze the stress,displacement and plastic deformation area,and finally the influence of cave location on the separated tunnel is obtained.After completing the above analysis,the location of the karst cave is reasonably set up,and a model group is set up to study the influence of tunnel shape on the stability of surrounding rock.The model is calculated,and the stress,displacement and plastic deformation areas are analyzed.Finally,the stability difference of the tunnel in different shapes is obtained.The conclusions are as follows:1.The distribution of maximum shear stress is related to the location of the cave.For the maximum principal stress,the location of the cave has a greater influence on the maximum tensile stress,and has little effect on the maximum compressive stress.When the karst cave is located in the middle of the tunnel,the maximum tensile stress of surrounding rock is larger.When the karst cave is located in the middle of the tunnel and at the top of the outside of the tunnel,the maximum tensile stress of surrounding rock is smaller.For the maximum shear stress,when the karst cave is located at the top or bottom of the tunnel,the maximum shear stress of surrounding rock is larger.2.The location of karst cave will affect the stress distribution and maximum value of surrounding rock of separated tunnel.When the karst cave is located in the middle part of the separated tunnel,the maximum displacement,the distribution range and the plastic deformation area of the separated tunnel are larger.When the cave is located in the same horizontal direction of the separated tunnel,the maximum displacement,the distributionrange and the plastic deformation range of the separation are smaller.3.When the karst cave is located in the upper middle of the separated tunnel,the sectional shape of the separated tunnel has some influence on the stress state of surrounding rock.For the maximum principal stress,the maximum tensile stress of surrounding rock is larger when the tunnel cross-section has a right angle,while the maximum tensile stress is smaller when the cross-section is an ellipse in the horizontal direction than the vertical direction;for the maximum tensile stress and the maximum shear stress,the influence of the tunnel cross-section shape is smaller.4.The section shape of the tunnel will have some influence on the displacement and plastic deformation zone of the separated tunnel.For displacement,when the section is circular or under the upper circle,the total displacement of tunnel surrounding rock increases,while when the section is rectangular or under the upper circle,the maximum displacement of tunnel surrounding rock is larger.For the distribution of plastic deformation zone,when the section is circular or rectangular,the plastic deformation zone of surrounding rock is larger,while when the section is elliptical or rectangular,the plastic deformation zone of surrounding rock is smaller. |
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