Research On Dynamic Stress Field Distribution Of Explosion Stress Wave Around Rock Cavity

Affected by crustal movement and man-made engineering,natural rock mass will form rock mass cavities of different shapes and sizes.In blasting engineering,explosives instantly release huge energy to form a dynamic stress field around the rock mass cavity.It is easy to form a dynamic stress concentration area,which affects the stability of the rock cavity.The properties of the rock cavity and the explosive have different influences on the shape of the stress concentration zone and the peak value of dynamic stress.Research on explosion stress wave propagation and dynamic stress distribution around cavity under different conditions from analytical and numerical methods:First,based on the wave function expansion method,taking the propagation of longitudinal waves around the limestone rock cavity as an example,the stress field formed by the coupling of the incident wave and the reflected wave is theoretically analyzed.And the dynamic stress of the rock cavity surface in the stress wave field can be solved.The results show that:As the radius of the rock cavity increases,the distance between the blast source and the center of the rock cavity decreases,the peak value of the normal stress gradually increases;With the increase of the circular frequency of the longitudinal wave,the peak value of the normal stress increases and gradually mo ves away from the direction of the explosion source.Secondly,ANSYS/LS-DYNA is used to analyze the stress wave propagation and dynamic stress field changes around the cavity caused by factors such as the distance between the explosion source and the cavity center,cavity size,explosive charge,cavity shape factor and the incident angle of stress wave.The calculation results show that:the reflected wave formed by the incident wave on the boundary surface of the cavity spreads radially to the surrounding,forming the reflected wave stress circle;As the distance between the blast source and the center of the rock cavity increases,the equivalent stress of these monitoring points decreases as a whole;With the increase of the radius of the rock cavity,the peak value of the equivalent stress at these monitoring points on the blast side keeps increasing,while the peak value of the equivalent stress at the monitoring point on the back blast side gradually decreases;As the explosive charge increased,the peaks of these monitoring points increased overall;As the shape factor gradually increases,the peak value on the blast side increases as a whole,and the peak value on the back blast side decreases as a whole;With the increase of the incident angle of the stress wave,the equivalent stress of the monitoring points on the blast side and the back blast side both increased to different degrees.Finally,a multi-factor comprehensive analysis is carried out on the equivalent stress peak value of the rock cavity surface.Under the condition of spherical cavity,as the radius of the cavity increases,the distance between the explosion source and the center of the cavity decreases,and the explosive charge increases,the maximum equivalent stress peak factor on the surface of the cavity increases continuously.And its direction is gradually approaching the direction of the explosion source.Under the condition of non-spherical cavity,the equivalent stress peak value and direction change are more complicated.When the shape factor is 0.5 and the incident angle is 20.5°,the equivalent stress factor takes the minimum value of 0.56,which is located in the direction of 91.57° of the cavity boundary surface.When the shape factor is 1 and the incident angle is 90°,the equivalent stress factor takes the maximum value of 1.21,which is located in the direction of 127.98° of the cavity boundary surface.