Study On Influence Of The Karst Caverns To Displacement And Stress Of DaBa Tunnel

Karst is one of the most frequently encountered geological environment in tunnel construction in mountain area,but the presence of such unfavorable geological phenomenon can pose a serious threat to the safety of the construction and operation of the tunnel.Once the excavation method in construction is unreasonable,the construction quality is substandard,the disposal of karst is improper,which all may cause hidden dangers such as local bias,collapse and so on.The occurrence of these disasters is not conducive to the on-site machinery and the safety of construction workers,and may affect the long-term operational safety of the tunnel as well.Therefore,structural analysis and studies on the stress characteristics and safety of the structures of Karst tunnels under complex geological conditions are of great importance on engineering value.This paper is based on DaBa tunnel and conducts statistics and analysis of karst appearing in DaBa tunnel and on-site data monitoring.In the following,taken Midas as numerical simulation software,the paper is focused on the influence of dry karst with different sizes,different spacing and different orientations on the tunnel displacement and stress of the surrounding rock.According to the influence of karst section of DaBa tunnel to rock displacement and stress by numerical simulation,the conclusions are shown as followings:(1)Affected by the karst at the top,the spandrel karst on the left,the horizontal krast on the left,the arch cave on the left,the karst cave at the bottom: the horizontal displacements of the arch on the left and right sides have increased when cokPared with no karst curves,and they will increase with the gradual increase of hole diameter ratio ?R and will decrease with the increase of radius ratio KD.(2)Affected by the karst cave at the top and the spandrel cave on the left: the displacements of settlement of crown and inverted arch relatively have increased when cokPared with no karst caves,and they will decrease with the gradual increase of hole diameter ratio ?R and will also decrease with the increase of radius ratio KD.(3)Affected by the arch cave on the left and the cave at the bottom: the displacements ofsettlement of crown and inverted arch will increase with the gradual increase of hole diameter ratio ?R and will decrease with the increase of radius ratio KD.(4)Affected by the top,left spandrel and left horizontal curves: maximum principal stress of the arch cave are presented as compression stress and the minimum principal stress of the karst curves at the bottom are all appeared as compression stress.(5)No matter how KD changes,the size relations between maximum principal stress of arch cave and the curves of all positions are as follows: the sequence from high to low is the arch curves at the left,the horizontal curve at the left,the spandrel curve at the left,the curve at the bottom and the curve at the top.The size relations between the curves of all positions and minimum principal stress of cave at the bottom are as follows: the curve at the bottom,the curve at the top,arch curves at the left,the spandrel curve at the left and the horizontal curve at the left.