Numerical Simulation Of Blasting Characteristics Of Artificially Frozen Clay

In order to meet the needs of national security and economics,more and more projects are being constructed in permafrost regions in the west of China.Along with the coal resources mining depth increases,the freezing temperature reduces to guarantee the freezing method tunnel excavation security.Drilling and blasting method is needed to solve the problem of high strength and low efficiency of traditional mechanical excavation of permafrost and artificial frozen soil.But the design and construction of drilling and blasting for frozen soil are based on the experience of rock blasting,which is very blind.In this paper,the blasting characteristics of artificially frozen clay are studied by means of theoretical analysis and numerical simulation,which provides theoretical basis and reference for blasting design of excavation engineering in frozen soil.The main findings and findings are as follows:（1）The parameter determination method of HJC constitutive model of artificially frozen clay is determined,and the artificially frozen clay is characterized differently under different negative temperatures.The parameter changes of the constitutive model related to utilization rate under different negative temperatures can accurately characterize the temperature effect and strain rate effect of frozen soil materials.（2）Based on the established HJC constitutive model parameters of frozen soil,the uniaxial instantaneous compressive strength test and SHPB of frozen soil were simulated.The dynamic and static mechanical properties of artificial frozen soil materials are basically reflected in the failure modes,strength characteristics and stress-strain curves.Under the action of impact load,artificially frozen clay shows obvious strain rate strengthening effect and temperature strengthening effect,with the decrease of temperature and the increase of loading strain rate,the peak stress and corresponding strain of frozen soil increase significantly.The stress-strain curves show obvious elastic-strain softening characteristics,and the reconstructed curves of numerical simulation results fit the peak stress and corresponding strain well,reflecting the stress-strain variation relationship before the frozen soil specimens are destroyed.（3）The dynamic mechanical properties of artificially frozen clay under dynamic and static-static load combination（low confining pressure）were studied by simulating the SHPB under active confining pressure.The effects of temperature,strain rate and confining pressure on the dynamic compressive strength of artificially frozen clay are analyzed and compared.It is concluded that temperature is the first factor affecting the dynamic compressive strength of frozen soil.（4）Taking 2#rock emulsion explosive as an example,a simple algorithm is adopted to calculate the unknown parameters of JWL equation.The accuracy of the calculated parameters was verified by two different experiments:numerical simulation of Power test and Hess test.The numerical simulation results of the two tests basically simulate the shape of the field test results.The sensitivity of detonation force and abruptness to the four parameters was analyzed,and the variation relationship and modification method of detonation force and abruptness about unknown parameters of JWL equation were determined.After modifying the calculated parameters,the error of detonation force and abruptness of simulation results was within 5%.The transformation of industrial explosives from engineering practice to numerical model is completed,which provides a feasible method for determining the parameters of JWL equation for common industrial explosives.（5）Theoretical calculations are made for different zone ranges under coupling and uncoupling single hole blasting structures of artificially frozen clay.The crushing zone of artificially frozen clay under different negative temperatures is several times that of rock drilling blasting,and the correctness of theoretical calculation is proved by numerical simulation.The size of fracture zone is calculated from two aspects of stress wave action and explosion gas action,and compared with the numerical simulation results,it is concluded that explosion gas action plays a leading role in the formation of artificial frozen clay fracture zone.（6）Numerical simulation of-5℃artificial frozen clay blasting crater is carried out,compared with artificial frozen clay,rock blasting crater and frozen soil materials from two aspects of crater shape and characteristic parameters of blasting crater.The shape of blasting crater of artificially frozen clay was summarized,and the critical burial depth of artificially frozen clay under 2#rock explosive was determined to be 1.356m·kg^-1/3,the optimal burial depth is 0.8598m·kg^-1/3,the standard throwing depth is 0.7221m·kg^-1/3and the loosening consumption is 0.39168kg/m³ the standard throwing is 0.4195kg/m³.According to the burial depth ratio,the types of blasting craters of artificially frozen clay under the action of 2#rock explosive are distinguished:when the burial depth ratio is less than 0.532,the strengthened throwing craters are used.When the buried depth ratio is greater than 0.532 and less than 0.634,the dropping crater is weakened.When the buried depth ratio is greater than 0.634,it is the loose blasting crater.