Numerical Experimental Study On Water Coupling Effect Of Open-pit Deep-hole Presplitting Blasting

As a directional fracture controlled blasting technology,presplitting blasting has been widely used in open-pit slope,hydraulic construction and railway traffic engineering to improve the stability of rock wall in reserved area.Water-bearing blast holes often occur in open-pit deep-hole presplitting blasting.Due to rainfall,groundwater and other factors,water medium appears in presplitting blast holes,and the original air decoupling charge structure is changed into water medium coupling charging structure.Water medium will seriously affect the effect of presplitting blasting and increase the damage to rock mass in reserve area.Therefore,the research on water-coupled presplitting blasting has important practical engineering significance.In this paper,the LS-DYNA dynamic analysis software is used to simulate the propagation process of explosive crack based on the damage function of RHT constitutive model,and the influence characteristics of water medium on presplitting blasting effect and the problem of water-coupled presplitting blasting under high ground stress are studied by comparing with the traditional air uncoupling charging condition.By establishing the cracking model of single hole blasting under different medium conditions,combined with theoretical calculation and numerical test results,it is found that the hole wall pressure,quasi-static pressure,peak stress and peak vibration velocity produced by water medium coupling charge blasting are significantly higher than those produced by air decoupling charge,and the time of explosion acting on rock mass is prolonged(21.3%).When the decoupling coefficient K_d=2,the radius of crushing zone and fracture zone caused by water coupling increases by 94%and 35%,respectively.By establishing the double-hole pre-splitting blasting model under different media conditions,the influence of two important parameters,decoupling coefficient and hole spacing,on the stress field,damage and crack growth of presplitting blasting was studied,and the related conclusions put forward the way to solve the problem of water hole presplitting blasting by optimizing the parameters.The results show that,compared with air decoupling,the blasting stress field produced by water coupling is stronger,which is beneficial to pre-splitting and joint formation,and also increases the damage to surrounding rock in reserve area.When the hole spacing(L=100cm)is constant,the pre-splitting effect is better when the decoupling coefficient K_d of air condition is between 2.5 and 3.3,and the decoupling coefficient K_d of water medium condition is between 4.0 and 5.0,which can effectively control the blasting damage to surrounding rock.The optimization results of blasting parameters are as follows:under air condition,the decoupling coefficient K_d is 3.3,and the hole distance L is100cm;Under the condition of water medium,the decoupling coefficient K_d is taken as 5.0,and the hole distance L is taken as 120cm.Therefore,the effect of water hole presplitting blasting can be improved by increasing uncoupling coefficient(1.9 times)and hole spacing(1.2 times),which can ensure the presplitting penetration and effectively reduce the blasting damage.By establishing the double-hole pre-splitting blasting model under different in-situ stress conditions,the in-situ stress initialization is solved by dynain file method,and the macro crack growth morphology of air-uncoupled and water-coupled pre-splitting blasting under different in-situ stress conditions is analyzed.The numerical test results show that the water medium plays an active role in the process of pre-splitting and fracture formation under high geostress conditions,that is,it can resist the inhibition and directional influence of in-situ stress on the pre-fracture propagation to a certain extent.