| The drill-and-blast method(mining method)has always been a common method for tunnel construction,and the proportion of construction projects using the drill-and-blast method in existing and under-construction traffic tunnels has reached about 70%.Smooth blasting technology has been widely used due to the advantages of small disturbance of surrounding rock and smooth and smooth excavation contour.However,in the actual construction process,due to the influence of multiple factors such as construction accuracy and environmental factors,tunnel excavation and blasting have the phenomenon of uneven excavation profile,and even the problem of over-under-excavation.Combined with the actual situation,each time the double-lane highway tunnel excavation and blasting produces an average of 10 cm of over-excavation,the direct cost of the initial support shotcrete construction will increase by 3 million to 4 million yuan per kilometer.According to the 1,400-kilometer road tunnels built by the drill-and-blast method in my country every year(the increment of highway tunnels in my country is about 2,000 kilometers per year),the related direct economic losses are as high as 4 billion to 6 billion yuan.Therefore,it is a key problem that tunnel engineering and blasting engineering field urgently need to solve to analyze the causes and influencing factors of over-under-excavation in tunnel excavation and blasting,and to propose feasible over-under-excavation control technology for excavation and blasting.Based on the Tunnel Qinjialing Project of the A3 Bid Section of Zhenba-Guang’an Expressway,this paper adopts the methods of on-site investigation,excavation and blasting test and numerical simulation to clarify the causes of over-under-excavation in tunnel excavation and blasting,and analyze the factors affecting over-under-excavation.,propose a smooth blasting scheme and control measures for over and under excavation suitable for Qinjialing tunnel.By collecting the data on the problems of over and under excavation in actual projects and on-site inspection,the reasons for over and under excavation are classified and summarized.The influencing factors of over and under excavation are divided into three categories: environmental factors,construction technology and construction management.The environmental factors mainly include the stability of the surrounding rock and the construction space of the tunnel face.When the surrounding rock has a certain stability,a certain distance can be created between the primary support and the tunnel face to ensure the drilling angle of the surrounding holes;construction technology The main technology is the rational design of the smooth blasting parameters of the surrounding holes,that is,the smooth blasting parameters should be optimized and adjusted in a timely and reasonable manner according to the changes of the surrounding rock,and at the same time to ensure that the charge structure,especially the distance between the charges of the axial uncoupled charge structure,must be The strength of the surrounding rock is reasonably determined;construction management means that the process of smooth blasting technology is carefully implemented through management means during the construction process,and the training of on-site operators is strengthened.According to the surrounding rock conditions at the entrance of Tunnel Qinjialing,the shape and size of the upper step section and the smooth blasting parameters of the surrounding holes,the ANSYS/LSDYNA software is used to establish a three-dimensional dynamic finite element calculation model that only includes the smooth blasting of the surrounding holes of the tunnel.Based on the observed over-under-digging data,the simulation calculation accuracy verification analysis was carried out.According to the calculation results,the error between the area of the over-excavation crack affected area of the original blasting scheme and the scanning results of the on-site section is 7.1%;the error of the area of the overexcavation crack affected area of the smooth blasting scheme and the scanning results of the on-site section is 15.25%,all within 20%.According to the background of Tunnel Qinjialing project,the blasting parameters such as the surrounding hole spacing,the thickness of the light explosion layer,the concentration of the charge,and the detonation velocity of the explosive are optimized through numerical simulation experiments.According to the numerical simulation test,the distance between the surrounding holes should be 50～55cm.Considering the drilling workload of the surrounding holes,the distance between the surrounding holes is 55 cm,the density factor of the blasting hole should be 1.1～1.2,the thickness of the light explosion layer should be 60～65cm,and the concentration of charge of the surrounding holes should be 0.07kg/m～0.11 kg /m,and the explosive around the hole should be a low-explosive explosive with a detonation velocity of about 2500 m/s.For the application of smooth blasting technology in Tunnel Qinjialing,the results of the on-site cross-section scanning test are compared with the cross-section scanning data of the original blasting plan.The maximum value is 0.323 m and it is reduced to about 0.125m;the economic benefit and cost analysis shows that the smooth blasting technology can save3.46147 million yuan. |
