Study On Over-excavation And Under-excavation Problems Of Smooth Blasting In Heterogeneous Rock Tunnels

When building a tunnel,it is inevitable that you will pass through areas with heterogeneous rock formations.Due to the complex and changeable conditions of the heterogeneous rock formations,tunnel blasting and excavation often have many conditions such as over-excavation and under-excavation,resulting in poor blasting quality.This article uses the Chongqing Shuangbei Tunnel For the engineering background,the Midas GTS NX software modeling and analysis method was used to study the blasting over-under-excavation problems under different structural surface inclination angles and lithological differences on both sides of the structural surface,and the blasting over-under-excavation under different blasting parameters was obtained.The increase or decrease law of the inclination angle of the structural plane and the ratio of the elastic modulus of the rock mass on both sides of the structural plane.The main research contents and results are as follows:Firstly,based on the heterogeneous rock section of the tunnel,use Midas GTS NX software to establish a three-dimensional numerical model of different structural surface inclination angles,and analyze the blasting over-under-excavation volume and structural surface of different charge structure,charge amount and surrounding hole spacing.The changing relationship of the inclination angle provides a basis for the optimal design of the smooth blasting scheme.Based on the heterogeneous rock strata where the project is located,this paper uses finite element software to establish three-dimensional numerical models of different combinations of rock masses on both sides of the structural plane.Through numerical simulation analysis,it is obtained that the existing tunnels are equipped with different charge structures and equipment.The increase and decrease law and relationship of the charge and the surrounding hole spacing during blasting with the ratio of the elastic modulus of the rock mass on both sides of the structural plane.Finally,it is proposed that the charge structure under the different lithological conditions on both sides of the structural plane,Optimized design scheme of charge and peripheral eye hole distance.Secondly,based on this article,relying on the engineering heterogeneous rock section,use Midas GTS NX software to establish a three-dimensional numerical model of different rock masses on both sides of the structural plane,and analyze the different charge structure,charge amount and peripheral hole spacing.The relationship between the blasting over-under-excavation volume and the elastic modulus ratio of the rock mass on both sides of the structural plane provides a basis for the optimal design of the smooth blasting scheme for heterogeneous rock formations.Thirdly,for the case where the lithology difference of the rock mass on both sides of the structural plane is too large,a design method of asymmetric charge and mixed asymmetric hole spacing is proposed.Numerical simulation results show that both asymmetric charge and mixed asymmetric hole spacing can better control over-under-excavation and improve blasting quality.