| The joint fractures generated in surrounding rock after drilling and blasting construction provide good channels for groundwater seepage and karst development,which change the engineering geological conditions of surrounding rock and development situation of karst.The tunnel lining structure will bear new risks under the comprehensive influences of groundwater and pressure of surrounding rocks with the whole lifecycle.However,the previous study on surrounding rocks stability and safety evaluation of tunnel lining structure rarely considered the changes of engineering geological conditions of surrounding rocks and karst development of surrounding rocks joint fractures.Therefore,it is of great significance for the safety evaluation of tunnel lining structure to study the joint fractures expansion law,engineering geological reconstruction method and the karst development trend of surrounding rock under the influence of drilling and blasting construction.Through theoretical analysis,site experiment,laboratory experiment and numerical analysis,this paper studied the joint fracture scope and expansion law of surrounding rocks under the blasting loading.Taking the Liaoshan tunnel of Ehan expressway as the researching subject,the karst development law and control elements were analyzed,the engineering geological conditions of surrounding rocks after drilling and blasting construction was re-built.On this basis,the karst development speed and trend of surrounding rocks were analyzed based on the carbonate rock dissolution experiment.Moreover,two modes of rupture failure（I-II tension-shear propagation failure and type II compression-shear propagation failure）and shear-slip failure of tunnel surrounding rock in karst process were established,and the safety of tunnel lining structure in the whole life cycle was evaluated.The main researching contents and conclusions are as below:（1）The three-dimensional model of the stress unit body of the surrounding rocks under blasting loading was established,and the crushing zone and fracture zone of the surrounding rocks were calculated respectively according to the unified strength theory and Mohr Coulomb strength criterion.The theoretical calculation results were moreconsistent with experiment results in site blasting.This calculation method is suitable for the calculation of joint fracture scope of tunnel surrounding rocks under blasting load acting.（2）According to the geological research of joint fracture of tunnel surrounding rocks and the numerical analysis on joint fracture of surrounding rocks under blasting load,the expansion law of joint fracture of surrounding rocks under blasting load acting were systematically researched.The results show that the joint fracture of surrounding rocks under blasting load was expanded along layers,and small fractures were generated between layers.The stress waves generated by blasting would be prevented by layers to a certain extent.The more broken the surrounding rocks were,the more fractures would be generated.But the fracture scope was small when the distance between layers was enlarged,the fracture of surrounding rocks would be reduced but the expansion scope of fracture was enlarged.（3）A method of engineering geological conditions reconstruction of tunnel surrounding rock considering the impact of drilling and blasting construction was established based on the calculation method of fracture zone range of tunnel surrounding rock and site fracture zone range detection proposed in this paper.This method provides a geological basis for the prediction of karst development trend of surrounding rock during tunnel operation.（4）Through the carbonate rock dissolution experiment,the corrosion rate and law of limestone and marl were studied.The results show that the static corrosion rate of limestone was about 0～0.158cm/year,and that of marl was about 0～0.267cm/year.When taking mechanical corrosion into consideration,the corrosion rate range of limestone was about 140～0.252cm/year,and that of marl was about 0.173～0.501cm/year.The calculation formula of mechanical corrosion rate of limestone was propoesd as vm=0.037Fr0.2（Lwh）0.5/year.The theoretical calculation result was more consistent with experimental result.（5）Taking Liaoshan tunnel of Emei-Hanyuan expressway as the research object,the karst development characteristics and control factors of tunnel surrounding rock were studied,and the karst development law of Liaoshan Tunnel was revealed.Based on the reconstruction of geological conditions,the karst development trend of Liaoshan tunnel was predicted.The results show that the development intensity and scale of karst in different positions of surrounding rocks could be ranked from strong to weak as:side wall>arch waist>inverted arch>arch crown.The karst development intensity and scale of surrounding rocks in left and right arch waist and left and right sides walls were asymmetrically distributed.The joint fracture nets with advantages control the local trends of karst development of surrounding rocks.During the dissolution and corrosion process of surrounding joint fractures,the expansion value of track length of surrounding joint fractures is 26.07～50.10cm when the tunnels are operated for 100 years.（6）Based on the statistical fracture mechanics of rock and the contact relationship between karst development position and joint fractures zone of surrounding rock,the instability failure mode of tunnel surrounding rock was is studied.Two modes of rupture failure（I-II tension-shear propagation failure and type II compression-shear propagation failure）and shear-slip failure of tunnel surrounding rock were proposed.Based on the reconstruction method of engineering geological conditions and numerical simulation analysis of surrounding rock stability proposed in this paper,along with the dissolution and corrosion expansion of joint fracture of surrounding rock,the stress of lining structure,displacement and equivalent plastic strain would have an obvious increment when the tunnel was operated for 50 years and 100 years,and the safety factor would be greatly reduced. |
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