Study On Crack Propagation Law And Control In Fractured Media Under Explosive Loading

Now blasting technology has been widely used in mining,transportation,water conservancy,hydropower and municipal and other fields.How to make rational use of explosive energy has always been a breakthrough problem in the blasting industry.The shock wave generated by explosive explosion in the borehole acts randomly on the borehole wall,which will inevitably form various explosive cracks around the borehole wall and cause certain damage to the surrounding rock.Therefore,in order to better master the controlled blasting technology and improve the blasting effect of rock mass,in-depth study of crack propagation characteristics under explosion load can be carried out.In this paper,PMMA is used as an experimental model.By combining theoretical analysis and experimental research,a single detonator load is carried out on the model of PMMA with a typical artificial crack.The influence of stress wave incident Angle and uncoupling coefficient on the propagation law of explosive crack was studied.Then,the range of stress wave incident Angle was reduced,and the wall casing with different materials was made.Through the blasting experiment of eccentric uncoupling wall protection,the propagation of the side explosive crack in the model surrounding rock was controlled.In the experiment,the strain characteristics of the media on both sides of the wall casing during controlled blasting were compared by using the super dynamic strain testing system to select the wall casing with better blasting effect.The main conclusions are as follows:(1)With the increase of incident Angle α,more stress waves will be reflected from the artificial cracks in the surrounding rock of the model,which will promote the growth of the main cracks around the hole,leading to the gradual increase of the total and average length of the main cracks.The failure of the surrounding rock side of the model is more and more serious than that of the photoblast side.With the increase of the decoupling coefficient K,the blast wave attenuates through the air in the hole,the pressure acting on the hole wall decreases,and the total and average length of the main crack decrease gradually.(2)The end of the artificial crack is subjected to the combined action of the reflected stress wave and the diffracted stress wave,and the wing crack is generated by the tensile stress superimposed by the two.The propagation direction of the wing crack is basically parallel to the incident direction of the stress wave in the explosion compression.When the incident Angle α is 0°,the wing cracks propagate parallel,which is beneficial to form a flat profile in the predetermined direction.When the incident Angle α is between 45° and 75°,the damage of surrounding rock side of the model is the least.When the incident Angle α is 90°,the compressive stress wave enters the artificial fracture vertically,and the explosion cavity begins to appear in the model.When the incident Angle α is 135°,there will be cambium cracks between the artificial crack and the hole,which is not conducive to the stability of the surrounding rock side.(3)When K=1.67,the incident Angle α is less than 90°,the cavity expansion coefficient of the model is 1.1,the diameter of the explosion cavity is slightly larger than the diameter of the bore,and the bore wall remains intact.After K>1.67,the blast wave attenuates rapidly in the air inside the hole,the energy acting on the model decreases,and the total and average length of the main crack decrease rapidly.In order to have more explosive energy acting on the medium and avoid explosion cavities as far as possible,the decoupling coefficient K is 1.67.(4)The total length of the main crack of the polyurea semicircle pipe was reduced by 54%compared with that of the casing model without wall protection.At the same time,the ratio of blast cavity area between the surrounding rock side and the photoblast layer side of the model is the smallest,and the hole wall of surrounding rock side remains intact.The length of the longest main crack on the side of surrounding rock is reduced by 74% compared with that of the photoexplosive layer.The peak value of lateral compressive strain of surrounding rock is24% lower than that of photoexplosive layer.The polyurea semicircle can effectively reduce the damage caused by the explosion stress wave to the surrounding rock side of the model.(5)In the blasting process of fractured rock mass,polyurea semicircular pipe can be used to carry out eccentric wall protection blasting on the surrounding holes.The incidence Angle of stress wave α is between 45° and 75°,and the decoupling coefficient is 1.67.It has good wall protection effect on the side of surrounding rock and strong crushing effect on the side of light blasting layer.