| Most rock masses in nature contain a large number of naturally formed joints,bedding and other structural planes.The existence of these joints has a great influence on the propagation and attenuation of explosive stress wave and the extension of explosive cracks,which makes it difficult to form a better smooth blasting contour surface and affect the blasting forming effect.Therefore,the study on the mechanism of blasting rock breaking of layered jointed rock mass has theoretical guidance and practical significance for improving the blasting effect of jointed rock mass.Based on the research results of scholars at home and abroad,the propagation law of explosive stress wave and the effect of blasting on layered jointed rock mass are further discussed and studied by combining theoretical analysis with numerical simulation.According to the field test of tunnel blasting engineering,the blasting design parameters are optimized,and the overbreak and underbreak are effectively reduced.It has a good market prospect and social benefits.The main contents and conclusions of this paper are as follows:(1)The blasting process of layered jointed rock mass and intact rock mass is analyzed by LS-DYNA software.The results show that the existence of joints can reflect and absorb the stress wave to a certain extent,which makes the stress wave attenuate sharply,restrains the development of cracks perpendicular to the joint direction,reduces the number of cracks in the vertical direction of the structural plane compared with the horizontal direction,and lays a foundation for the design of smooth blasting parameters of layered rock.(2)The attenuation law of explosive stress wave propagating through different joint strength is studied from three aspects:the distance between joint and borehole,joint width and joint strength.Three groups of joints with different strengths-joint I,joint II and joint III are selected,and three kinds of joints with different widths-5 cm,10 cm and 15 cm are combined in each group of joint strength.A total of nine groups of models are used for numerical simulation.(3)The influence of the angle between adjacent boreholes and joint sandwich on the formation of photoblasting surface is analyzed.The effect of the angle between the layer structure plane and the borehole core line on the blasting effect was studied under six working conditions:0 30 45 65 and 90 respectively.The results show that the concave-convexity of fracture surface increases with the increase of angle between 0?45.When the angle is 45 the concave-convexity of fracture surface reaches its maximum,and there is no smooth blasting surface between boreholes.When the angle between 45~90,the concave-convexity of fracture surface is inversely proportional to the angle between joints.(4)In view of the problems and reasons in engineering,the influence of "empty holes" on the blasting effect of jointed rock mass is studied.Through comparison,it can be seen that when"empty holes" are set at the joints between adjacent holes,the cracks produced by the two holes can better meet and form through cracks.Combining with the field test of tunnel blasting engineering,the blasting shaping of different parts of layered rock tunnel is poor.In addition,the optimum design method of blasting parameters for layered rock tunnel is put forward. |
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