| To promote the coordinated development and complementary utilization of resources in China,as the strategy of large-scale development in the western region is being implemented vigorously,the construction of infrastructure in the western region has ushered in a boom,such as projects like "West-East Gas Transmission","Belt and Road Initiative",and the Sichuan-Tibet Railway.In the high-cold regions of the west,construction projects often encounter issues with frozen rock and soil blasting excavation.In order to ensure the safe and efficient production of open-pit mines in high-cold regions,it is necessary to explore the dynamic response of rock masses and the blasting characteristics under the high-altitude and cold environment,and reveal the blasting mechanism of rock mass in high altitude cold area environment,so as to solve the issues of existing rock breaking theories and blasting technologies that are not applicable to the safe and efficient mining in open-pit mines in high-cold regions.This paper first takes the typical rocks of the Yulong Copper Mine in Tibet as the research object,conducts static mechanical property tests under different freezing temperatures and saturation conditions,combines with numerical analysis using PFC3 D,and discusses the macro-micro mechanisms of freezing rock expansion effects.Then,dynamic mechanical property research is conducted using the SHPB system,analyzing the energy consumption characteristics of impact and fragmentation of frozen rocks,and establishing a dynamic constitutive model considering initial damage effects.Based on this,by conducting indoor blasting model experiments of frozen sandstone,the process of crack propagation during blasting,the characteristics of blasting fracture,the law of strain wave propagation,the establishment of stress wave attenuation equations,and the derivation of theoretical calculation formulas for crack zone radius are captured.Finally,combined with the research on the explosive mechanical properties and formulation improvement of high-altitude emulsion explosives and field step blasting tests,the blasting fragmentation characteristics of frozen rocks are investigated.The following conclusions are obtained.(1)The freezing action has a greater impact on the strength of saturated rocks than on the strength of dry specimens.The freezing action changes the failure mode of the specimens and is related to the rock properties.For example,frozen schist mainly exhibits shear failure,while frozen sandstone shows a mixed tensile-shear failure mode.In the frozen rock PFC3 D model,the maximum contact force and contact amount between particles are affected by the deformation of rock particles and water particles.The damage to the specimens is more influenced by the freezing expansion deformation of water particles,and the lower the temperature,the greater the impact.(2)Under negative temperature conditions,the phase change of water ice can result in dynamic strength enhancement or degradation of specimens.Freezing effects at-10°C and-20°C enhanced the strength of sandstone,while the freezing effect at-10°C improved the strength of granite specimens,but at-20°C it caused frost damage.The newly developed dynamic damage constitutive equation can better fit the dynamic stress-strain curves of both types of specimens.The fractal dimensions of saturated frozen sandstone and granite mainly range between 1.5～2.6 and 1.7～2.4 respectively.Saturated freezing action increased the integrity of the specimens,with the energy absorption of frozen sandstone specimens higher than that of normal temperature sandstone specimens,resulting in higher strength of the former and more obvious strain-rate effects.(3)In the propagation process of cylindrical stress waves,the strain wave’s decrease corresponds to a different form of work compared to the increase.The rate of energy accumulation in the decrease of the strain wave is greater than the rate of energy release in the increase.Under the action of cylindrical stress waves on rock media,the strain rate gradually decreases with increasing distance from the blast center,and the damping characteristics of water reduce the strain rate of the specimen.The explosive strain wave in the crack zone decays exponentially,with the peak strain decay rate of water-saturated frozen rock being higher than that of dry rock,and the lower the temperature,the faster the former decays.The average fragmentation degree of the thrown blocks at the funnel of the water-saturated frozen specimen is higher than that of the dry specimen at negative temperatures,with the former having a slightly smaller fractal dimension than the latter,and the water-saturated frozen rock has fewer explosive cracks than the dry rock.(4)The dynamic elastic modulus of the rock mass in the fissure zone gradually decreases with the increase of the distance from the explosion center.The stress wave attenuation is different from the strain wave attenuation process,the former follows a power function decay law.The radial peak stress of the frozen saturated rock in the blasting fissure zone is smaller than that of the same explosion center distance in the rock at normal temperature and dry conditions,with the former decay index generally greater than the latter.The fissure zone radius gradually decreases with the increase of dynamic tensile strength.The dynamic mechanical parameters of the rock are enhanced after freezing,the rock mass becomes less prone to blasting,and the quasi-static effect of explosive gas at low temperatures is weakened,ultimately leading to the radius of the crushing zone and the fissure zone being smaller than in the rock at normal temperature and dry conditions.(5)The particle size of on-site mixed emulsion explosives increases with altitude within a certain range,showing a trend of initial increase followed by decrease.The number of effective bubbles decreases with the increase of altitude.Within a certain range,the detonation velocity and peak pressure of shock wave of on-site mixed emulsion explosives are negatively correlated with the particle size and altitude,and the decrease in particle size with increasing altitude will reduce the attenuation of detonation velocity and peak pressure of shock wave.Compared with traditional emulsion explosives,the addition of PPG in high-altitude environments reduces bubble diameter,increases quantity,improves stability,and enhances explosive mechanical properties.Using the axial air gap loading method can improve the distribution of blasting energy in frozen layer rock masses,reduce oversize rate,adapt formula explosives to low temperature and low pressure environments,enhance blasting safety and stability,and reduce overbreak and rock base remaining phenomena.Figure [103] Table [34] Reference [166]... |
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