| With the rapid development of China’s water conservancy industry and the deepening of the Western Development Strategy,there are more and more newly constructed and planned water diversion tunnels and water conveyance tunnels that need to pass through layered rock mass.The drilling and blasting method,as one of the widely used methods for excavation of such hydraulic tunnels,may be affected by various factors such as existing structural planes in layered rock mass,leading to a complex distribution of rock blasting damage.This study establishes a blasting model for layered rock mass in order to investigate the characteristics of blasting damage distribution in the surrounding rocks of water diversion tunnels through layered rock mass.It explores the effects of single-point and multi-point blasting sources,earth stress,structural plane thickness,structural plane position,number of structural planes,and explosive charge coupling coefficient on the blasting response and damage distribution in layered rock mass.Based on the 30 th water diversion tunnel of the West Main Canal of the Yellow River Irrigation Project,the study investigates the blasting excavation effect of conventional blasting design schemes in water diversion tunnels through layered rock mass and proposes optimization schemes for blasting in such tunnels.The main research contents and results are as follows:(1)Theoretical analysis shows that the propagation of blasting stress waves in rocks is related to the density and Poisson’s ratio of rock materials.If the impedance of the explosive wave matches the impedance of the rock wave(close to consistency),better blasting effects can be achieved.Due to the existence of structural planes and filling materials in layered rock mass,the blasting stress waves will reflect and transmit at the structural planes,changing the curvature of the stress wave surface and causing tensile stress to lead to rock damage.(2)The closer the distance is to the blasting source,the greater the attenuation of the blasting vibration velocity;the farther the distance is from the blasting source,the smaller the attenuation of the blasting vibration velocity.When there are multiple blasting sources in the rock,the attenuation rate of the blasting vibration velocity will be reduced.For the RHT model of purple sandstone,the radius of the blasting crushing zone is approximately three times the radius of the explosive charge,and the maximum self-stabilizing range of the rock mass after blasting damage is approximately 3.5 times the radius of the explosive charge.Horizontal earth stress has a greater effect on the development of blasting fractures that are perpendicular to the direction of higher earth stress in rocks,but has less impact on the blasting crushing zone.(3)The rock blasting vibration velocity at the structural plane is higher than that at the same position in homogeneous rock.Therefore,the rock damage zone tends to develop towards the inside of the structural plane.The thicker the structural plane,the greater the obstacle to the blasting stress wave,and the larger the non-coupling coefficient of the explosive charge per penetration of the structural plane,the smaller the proportion of the rock blasting crushing zone.Therefore,in the blasting design of layered rock mass,the layout of boreholes should avoid positions where structural planes develop or increase the non-coupling coefficient of the explosive charge at positions where structural planes occur.(4)When conventional blasting design methods are applied in homogeneous rock water diversion tunnels,good blasting excavation results can be achieved.In homogeneous rock water diversion tunnels,the blasting profile line is basically consistent with the tunnel design profile line,and the over-excavation area is mainly distributed in the side walls and arch shoulders,with a maximum over-excavation amount of 13.3cm,which appears in the tunnel arch shoulder.If conventional blasting design methods are used in layered rock water diversion tunnels,the blasting excavation effect is poor,and the over-excavation area mainly grows strip-shaped along the structural plane,with an average over-excavation length of about170 cm and a width of about 4cm.The distribution position of the farthest end of the rock blasting damage area is about 60 times the charge radius away from the tunnel design profile line.When the structural plane angle coincides with the direction of most of the drilled holes,there will be a nearly two-fold damage to the tunnel radius.(5)In light of the research results,optimal blasting designs were made for representative horizontal layered rock water diversion tunnels.The over-excavation in the surrounding rocks of the layered rock tunnels are significantly reduced,and the maximum over-excavation is located at the arch shoulder where the over-excavation is reduced by approximately 10 times,making the over-excavation magnitude comply with the standard limit. |
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