Response Characteristics And Safety Criteria Of Surrounding Rock Of Adjacent Tunnels Under Blasting Vibration

The construction of underground tunnels plays a key role in supporting the steady implementation of China’s "transportation power" strategy and the grand initiative of the "One Belt and One Road".As a common method of tunnel excavation,the drilling and blasting method can improve the construction efficiency,at the same time,the negative effect of blasting vibration generated by it makes the surrounding rock burst,block loosening and sliding and other dynamic disasters of adjacent tunnels frequently.How to control the negative effects of blasting vibration is one of the key scientific issues for the safe and efficient construction and operation of underground tunnels.This paper takes the blasting vibration hazard in the adjacent tunnel surrounding rock as the research background,and comprehensive use the methods of field test,theoretical analysis and numerical simulation,etc.,carried out a series of research works on several issues such as "the propagation and prediction of blasting vibration in the adjacent tunnel surrounding rock,the instability and slip mechanism of the adjacent tunnel surrounding rock blocks under the action of blasting vibration,the relationships between blasting vibration response of the adjacent tunnel surrounding rock and RMR(Rock Mass Rating),and the safety criteria of blasting vibration in the adjacent tunnel surrounding rock”.The specific research contents and achievements are as follows:(1)Based on field tests and LS-DYNA-3DEC simulation,the propagation and attenuation characteristics of blasting vibration in adjacent tunnel surrounding rock is studied,the feasibility of using empirical equation to predict blasting vibration in adjacent tunnel surrounding rock is discussed,and the PPV(Peak Particle Velocity)prediction equation of blasting vibration in adjacent tunnel surrounding rock considering tunnel cavity effect is established.The study shows that the PPV of blasting vibration in surrounding rock of adjacent tunnel can be predicted,while the dominant frequency of blasting vibration is less effective.The PPV prediction equations for blasting vibration in adjacent tunnel surrounding rock constructed by considering the tunnel cavity effect(diffraction and reflection characteristics of blasting vibration wave in tunnel surrounding rock)are more accurate than the traditional empirical equations.(2)Based on the theory of stress wave propagation,the analytical models of dynamic instability and sliding of rectangular key blocks of tunnel roof surrounding rock are established,and the mechanism of dynamic instability and sliding of rectangular key blocks of tunnel roof surrounding rock and the main controlling factors of instability and sliding are discussed.Based on discrete element UDEC numerical model,the dynamic instability and sliding mechanism of non-rectangular key blocks of tunnel roof surrounding rock and the influence of block shape on block sliding characteristics are studied.The sliding displacement of the key block at the roof of the tunnel is mainly related to the initial normal stress of the joints,joint stiffness,friction angle,wave amplitude,frequency,incidence angle,and the size and shape of the block.For the rectangular key block of the tunnel roof,the smaller the initial normal stress of the joints the greater the joint stiffness,the larger the amplitude,the lower the frequency,the smaller the incidence angle,and the larger the size of the block,the larger the sliding displacement of the block will be;for the key parallelogram block,the sliding displacement of the block decreases with the decrease of joint angle(the angle between the bevel and the horizontal plane);for trapezoidal key blocks and wedge-shaped key blocks,the sliding displacement of the blocks increases gradually with the decrease of joint angle.(3)The RMR quantitative characterization method and process of discrete element 3DEC numerical rock tunnel model are given.Through a series of LS-DYNA-3DEC numerical models,the relationships between blasting vibration response PPV,dominant frequency,sliding displacement,damage plastic zone of surrounding rock and RMR of surrounding rock is systematically explored.The change of surrounding rock RMR mainly considers the mechanical properties of the surrounding rock block,the distribution characteristics,density and weathering degree of joints.On the whole,with the decrease of RMR of the surrounding rock,the PPV and dominant frequency of blasting vibration of adjacent tunnel surrounding rock decrease,and the maximum sliding displacement of surrounding rock block increases.At the same time,when the reduction of RMR of surrounding rock is mainly controlled by the rock block properties,the damage of the adjacent tunnel surrounding rock not only includes the block slip,but also includes the tensile or shear failure of the surrounding rock block.The lower the RMR,the more easily the surrounding rock block of the adjacent is damaged.(4)Based on the sliding displacement and damage plastic zone of adjacent tunnel surrounding rock under single blasting vibration,three damage degrees of adjacent tunnel surrounding rock is determined.Based on the statistical analysis of data,the relationship between the block sliding displacement,damage plastic zone of adjacent tunnel surrounding rock with different RMR and the PPV and dominant frequency of blasting vibration is discussed,and a "double factor" safety criterion for the PPV and dominant frequency of blasting vibration of adjacent tunnel surrounding rock considering RMR of surrounding rock is established.By comparing with the existing national blasting vibration safety standards,scholars’ research,on-site observation and simulation,the usability of the proposed criteria is verified.The criteria in this paper starts from the sliding displacement and damage plastic zone of adjacent tunnel surrounding rock blocks,and comprehensively considers the influence of RMR of surrounding rock,blasting vibration PPV and dominant frequency,which has certain engineering practicability and reference significance.