| In the construction of tunnel engineering in karst area,because of its complex engineering geology and hydrogeological conditions,the tunnel is prone to serious karst geological disasters during the construction period.In order to ensure the safety and order of tunnel construction,it is of great significance for tunnel construction to carry out risk assessment of water inrush and mud and the influence of surrounding rock stability.This article is based on the Jiu Zhou tunnel,in view of the risk of water inrush and the instability of surrounding rock in construction,the above problems are studied by means of field investigation,geological prediction,field monitoring,fuzzy comprehensive evaluation and numerical simulation,from the hydrogeological characteristics of karst tunnels,the risk of water inrush and collapse and the angle of the deformation characteristics of surrounding rock.The main contents and conclusions are as follows:1.Through theoretical study and analysis of the hydrogeological conditions of the karst development of the Jiu Zhou tunnel,the water inflow of the local section of mileage K5+660~K6+980 is predicted by the method of groundwater dynamics,and the maximum water gushing amount is 25275.6m~3/d.Based on the engineering example of the geo radar,the radar image features of the complete surrounding rock,the fractured fractured zone and the filled karst are studied and summarized from the analysis of the"six bit features"of the radar image.2.By selecting the main controlling factors affecting the water inrush,the fuzzy comprehensive evaluation model for water inrush from the tunnel is built,the judgment matrix is constructed by the“1~9”scale method,and the membership function matrix is established based on the expert scoring method to construct the tunnel.Water inrush mud risk,landslide risk probability and hazard degree membership model.Finally,based on the maximum membership degree principle,the risk grade of water inrush mud in mileage ZK6+075 is a moderate risk.The yellow warning signal should be issued.The risk grade of karst collapse at the ZK5+992 section belongs to high risk,and the orange warning signal should be issued.3.First,the analysis and calculation of the safe thickness of the rock plate between concealed karst cave and tunnel are carried out.Secondly,the influence law of the stability of surrounding rock under various forms,such as karst cave position,surrounding rock grade,equivalent water pressure,side pressure coefficient,rock plate thickness and combined karst cave,is carried out by FLAC3D numerical calculation software.The results show that,when the grade of the surrounding rock is grade V,the equivalent water pressure is more than 1MPa,the side pressure coefficient is more than 2,the thickness of the rock plate is less than 2m,and the filling hidden cave in the tunnel side exists,the rock disc between the tunnel and the hidden cave will appear the shear active plastic zone,and the stability of the surrounding rock is poor.By comparison,the difference between field monitoring value and simulation result is less than 6%,and the simulation results are more accurate.4.The influence of groundwater seepage on the stress and deformation characteristics of surrounding rock is discussed.In view of the potential hidden karst cave in the middle rock column and the arch foot,the influence of the size of the karst cave and the water pressure on the surrounding rock is studied.The results show that when the groundwater level is higher than 60m and the grade of surrounding rock is gradeⅤ,when the diameter of the cave is greater than that of 4m and the karst water pressure is less than 0.25MPa,the rock disc between the tunnel and the karst cave will appear through the tensile shear active plastic zone,and the stability of the surrounding rock is very poor.By comparison,the difference between field monitoring value and simulation result is less than 8%,and the simulation results are more accurate. |
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