Study On The Breaking Law Of Frozen Soil Layer In Open Pit Blasting Of Yulong Copper Mine

The frozen soil layer of open-pit mines in alpine regions is the main factor affecting the blasting effect.In order to reveal the breaking law of the frozen soil layer of open-pit mines in alpine regions under the impact of blasting load,indoor mechanical tests were carried out to analyze the dynamic relationship between the mechanical strength of frozen soil and temperature.Combined with the mechanical theory of cantilever beam,a simplified cantilever beam model of frozen soil layer breaking under explosive load was established to obtain the calculation formula of the breaking length of frozen soil layer,the combined blasting method of deep and shallow holes in frozen soil layer is improved,and the following conclusions are obtained:(1)According to the temperature measurement data of frozen soil,the temperature variation law of frozen soil at different burial depths is studied;It is found that the main factors affecting the formation of frozen soil are temperature and the burial depth of frozen soil.The temperature of the shallowly buried frozen soil layer is significantly affected by the environment,while the deeply buried frozen soil is less affected by environmental changes.After a certain burial depth,the annual ground temperature starts to rise.The annual variation range of the temperature of the frozen soil layer of Yulong Copper Mine is-12～9℃.(2)The relationship between basic mechanical parameters of frozen soil and freezing temperature is summarized by carrying out freezing mechanical property tests under different freezing temperatures and freezing times,including uniaxial compression,brazilian splitting and shear tests.The test results show that the compressive strength,elastic modulus and tensile strength of frozen soil decrease linearly with the increase of freezing temperature,and the relationship between the mechanical parameters of frozen soil layer and temperature is obtained,in which the compressive strengthσ_c=224.55-175.22T,tensile strengthσ_t=0.86-0.088T,elastic modulus E=3.43-6.06T;The shear strength,cohesion and internal friction angle increase with the decrease of freezing temperature.At the lowest temperature of the frozen soil layer,the internal friction angle of the frozen soil layer is 34°,cohesion is 8.1 KPa,and the shear strength is 5.8 KPa.(3)Based on the cantilever beam theory,the fracture mechanics model of the frozen soil layer overlying the ore rock under the action of explosion load is established,and the fracture rule of the breaking length of the frozen soil layer under the impact of the breaking is deduced.It is found that during the blasting process,the frozen soil layer is separated from the underlying rock layer,and the frozen soil layer breaks at the maximum bending moment of the cantilever beam structure.With the continuous decrease of the soil temperature,the thickness and tensile strength of the frozen soil layer are increasing,and the breaking length of the frozen soil layer is gradually increasing.(4)In order to solve the problem of blasting frozen soil mass in the open air,combined with the actual working conditions of Yulong Copper Mine,the deep and shallow hole combined blasting scheme was improved according to the breaking law of frozen soil,and was successfully applied in Yulong Copper Mine in Changdu,Tibet.The maximum fracture length of frozen soil under the impact of blasting in Yulong Copper Mine was 6 m,and the rate of frozen soil mass was controlled within 4%,effectively reducing the generation of frozen soil mass.