Feasibility Study On Full Section Construction Of Soft Surrounding Rock Tunnel Based On Smooth Blasting

With the rapid development of infrastructure construction in China,the mileage of highway and railway tunnels is increasing,and the weak surrounding rock with poor geological conditions is becoming more and more common in the process of tunnel construction.Because of its low strength and easy deformation,the traditional construction methods all adopt partial excavation to ensure the stability of surrounding rock,which greatly reduces the construction efficiency.With the continuous improvement of the mechanization level of tunnel construction,the time of drilling,blasting and support is greatly shortened,which provides favorable conditions for the high-efficiency full section excavation to be applied in the soft surrounding rock.At the same time,targeted and reasonable blasting and excavation methods are also needed to ensure the safety and stability of surrounding rock.Based on the V-level soft surrounding rock section of Liyue road tunnel,this paper determines the reasonable blasting and excavation process parameters,applies the optimization scheme to the site and evaluates the blasting effect qualitatively and quantitatively,analyzes the influence and weight of excavation process parameters on surrounding rock deformation,and finally puts forward the effective full section construction method applicable to soft surrounding rock.The main research contents and conclusions are as follows:(1)According to the engineering characteristics of soft surrounding rock,a multi-level blasting parameter simulation test is designed.The results show that the blasting effect is the best when the millisecond of blasting parameter value is set to10 ms,the diameter of peripheral hole is set to 40 mm,the spacing of peripheral hole is set to 34 cm,and the total charge per cycle is 42.55kg;The appropriate evaluation index and scoring method of blasting effect are determined.The weight of each index in the evaluation of blasting effect is obtained by AHP.The quantitative description of blasting effect is made and the evaluation set of blasting effect is established.Through the orthogonal experiment,the optimal value of the whole section excavation process parameters of soft surrounding rock is studied,and the influence rules of different parameters on the surrounding rock deformation are obtained.The results show that the reinforcement coefficient of advance support is negatively related to the size of the surrounding rock deformation,the follow-up distance of invert is positively related to the size of the surrounding rock deformation,and the influence of the short distance of the second lining on the size of the surrounding rock deformation is relatively small.(2)Through the orthogonal experimental design,the optimal value of the full face excavation process parameters of the soft surrounding rock is obtained,and the influence rules of different parameters on the surrounding rock deformation are obtained.The results show that the reinforcement coefficient of the advance support is negatively related to the surrounding rock deformation,the follow-up distance of the inverted arch is positively related to the surrounding rock deformation,and the influence of the second lining and the short distance on the surrounding rock deformation is relatively small;Through range analysis,the influence weight of each parameter on surrounding rock deformation is ranked from large to small as follows:advance support strengthening coefficient,second lining following distance and inverted arch following distance;the value of advance support strengthening coefficient is determined to be 1.6,inverted arch following distance is 20 m and secondary lining following distance is 70 m,which is the best combination of process parameters.(3)Based on the principle of the least square method,the combination of the best process parameters is confirmed by the intelligent optimization design,and the results of the two optimization methods are consistent;The accumulated horizontal convergence and the accumulated settlement of the arch crown shall not exceed the limit relative displacement calculated according to the design code.(4)This paper puts forward the construction process of full face excavation for the soft surrounding rock tunnel,and puts forward the key points of operation for the quality control of the construction process such as advance support,smooth blasting,initial support and inverted arch construction,forming the full face construction method for the soft surrounding rock tunnel.