| In recent years,with the rapid development of the economic construction,the state has invested more and more money in the infrastructure construction,and infrastructure construction will play an impormentant role in the development of the national economy.Drilling and blasting construction techniques are widely used in the excavation process of underground engineering,and gradually penetrate into various fields such as water conservancy and hydropower,mining and tunnel engineering.Because the rock mass is a product of long-term geological action,the interior is often accompanied by defects such as joints,cracks,bedding and weak interlayers.These defects will be damaged in advance under the blasting load,which seriously affects the rock mass structure and leads to blasting construction.In the actual contour,the phenomenon of over-under-excavation is very serious,and the effect of rock mass blasting is not good,which directly affects the construction progress,construction quality and construction cost of the tunnel project.In order to study the internal crack propagation mode and interaction law of fractured rock mass,this paper combines the theoretical analysis of crack propagation in fractured rock mass with indoor test methods,and obtains the following results:(1)According to the theory of blasting impact,after the explosive is detonated,the blasting load breaking rock is mainly divided into the guiding action of the explosive stress wave and the crack propagation under the action of the explosive gas.The numerical analysis is used to calculate the deflection angle of the prefabricated crack tip.The results show that the attenuation of the explosion stress wave propagates to the tip of the prefabricated crack,and the load generated by the stress wave is insufficient to cause the crack propagation at the tip of the prefabricated crack,which only causes the damage and deformation of the material at the tip of the prefabricated crack,thereby guiding the expansion of the secondary cracks(2)Conducting laboratory tests on fractured media,the test found that:(1)The crack initiation direction is the result of the interaction between the explosion stress wave and the prefabricated fracture,and has a guiding effect on the crack propagation of the prefabricated fracture tip.(2)The existence of prefabricated cracks affects the propagation of stress waves,and also affects the interaction between the explosive gas and the crack.Different prefabricated crack arrangements will lead to a difference in crack propagation velocity and crack tip stress intensity factor.(3)Crack propagation during the process of rock fragmentation is divided into two processes: stable expansion and steering expansion.The steady propagation crack tip has a large moving speed,the moving path is a straight line,and when the crack direction changes,the crack tip moves at a slower speed and the tip stress intensity factor fluctuates.The cracks in the two extensions will affect each other within a certain distance,which leads to the simultaneous change of the crack tip velocity and the stress intensity factor.(3)For the single-fracture medium,the difference between the angle between the pre-formed crack and the connection direction of the blasthole will directly lead to the difference of the crack propagation pattern,thus affecting the final blasting line from the design contour,when the angle is 30°,the contour of the explosion has an obvious “Z” shape feature;when the angle is 45°,the contour of the explosion has obvious over-excavation phenomenon;For the multi-fracture medium,the pre-formed crack spacing has a great influence on the final failure mode of the crack.When the distance between the secondary crack derived from the external pre-formed crack tip and the internal crack penetration point is small,the explosive gas escapes less,the blasting effect is more. |
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