Research On The Structural Safety Of Tunnels With Broken Surrounding Rock Under The Combined Action Of High Water Pressure And Earthquake

During the"14th Five-Year Plan"period,the construction of highways in west and Tibetan area will be vigorously promoted.Under such an extremely complex geological environment,the construction and operation of tunnels will face severe tests.There are many water systems and active fault zones in western Tibetan area,with abundant precipitation every year.Under such conditions,high water pressure and high seismic intensity are the outstanding problems that Tibetan tunnel projects will face.Therefore,it is of great significance to study the structural safety of highway tunnels under the combined action of high water pressure and strong earthquakes.In this paper,the typical high water pressure tunnels of Wenchuan-Maerkang Highway are used as the supporting project.And the methods of field investigation,literature investigation,field monitoring,numerical simulation,mathematical model,etc.are used to study the structural mechanics characteristics and safety of tunnel engineering in Tibetan areas under the combined action of high water pressure and strong earthquakes.The research carried out and the results obtained are as follows:（1）The water disasters of Feixianguan Tunnel of Yakang Highway and Miyaluo No.3Tunnel of Wenma Highway was investigated.On this basis,long-term structural health monitoring was carried out on the typical high water pressure tunnels of Wenma Highway--Miyaluo No.3 Tunnel and Shiziping Tunnel.Through the analysis of monitoring data,the evolution law of the structural mechanics characteristics of Miyaluo No.3 Tunnel during the construction period and early completion was studied.Then,with the Miyaluo No.3 Tunnel as the engineering background,the fluid-solid coupling numerical simulation was carried out to study the change law of the seepage field and the long-term mechanical properties and safety of the tunnel structure.（2）On the basis of studying the structural mechanical properties of the tunnel under high water pressure,the influence of strong earthquake superposition is further considered.Based on the time-history method and the finite difference software FLAC^3D,the superposition calculation of high water pressure and earthquake was developped.The dynamic response and mechanical characteristics of the tunnel structure under different water head heights,different tunnel depths and different seismic acceleration peaks were studied.The results showed that when the height of the water head reached 50m and the peak seismic acceleration reached 0.3g,the safety factor of the lining structure will not meet the requirements of the code.（3）Based on the cloud model theory,a structural safety assessment model for highway tunnels in Tibet under the combined action of high water pressure and strong earthquakes was established.Starting from the regional characteristics,geological and climatic characteristics of Tibetan areas,the factors affecting structural safety under the combined action of high water pressure and strong earthquakes were analyzed.Then,a hierarchical index system was established,and the index weights were calculated.The safety level of the structure was divided into Ⅰ～Ⅳ levels,and each index was quantified to standard level interval.Through the inverse cloud generator,the cloud digital characteristics of each index were calculated.And the weighted calculation was used to obtain the final comprehensive evaluation cloud digital characteristics.Through the forward cloud generator,the comprehensive evaluation cloud shape was generated.A total of 4 sections（3 high water pressure sections and 1 general section）of Miyaluo No.3 Tunnel and Shiziping Tunnel were evaluated,then the evaluation results were compared with the numerical calculation results.The two results were in good agreement,and the assessment results based on cloud model were more conservative.