Study On Breaking Law Of Surface Frozen Layer In Cold Plateau Area Under Blasting Load

The surface frozen layer is the main factor affecting the blasting effect of open-pit mine in plateau cold region.When the conventional blasting scheme is adopted,it is easy to produce large chunks of frozen layer.In order to deeply explore the breaking law of surface frozen layer in cold plateau region under blasting load,this thesis studies the research methods of theoretical analysis,indoor test and numerical simulation,aiming at providing theoretical reference for open-pit mining and blasting operation in cold plateau region.The main research contents and achievements are as follows:Firstly,according to the actual blasting conditions of open-pit mine in cold plateau region,based on structural mechanics theory,dynamic characteristics and blasting theoretical equation,the structural mechanics model of surface frozen layer breaking in cold plateau region is established by using the related information of blasting stress wave and gravity of frozen layer between blasting holes,and the breaking law of frozen layer covered with artificial gravel on surface seasonal frozen soil is explored.The results show that the thickness of frozen layer,the friction coefficient of frozen layer between blasting blast holes and the packing section in blasting blast hole,the overall tensile strength of frozen layer with heavy frozen layer are positively correlated with the critical fracture length of frozen layer,and the impact pressure of stress wave generated by charge explosion into frozen layer between blasting blast holes is negatively correlated with the critical fracture length of frozen layer;The influence of physical and mechanical properties of the second layer of natural frozen soil on blasting effect is higher than that of the surface layer of artificial gravel frozen soilSecondly,frozen uniaxial compression and Brazilian splitting direct shear tests were carried out on the surface frozen soil samples taken from plateau open-pit mines.The results show that the freezing rate of frozen depth of frozen soil is approximately linear or multi-stage linear with time affected by temperature.The lower the freezing temperature,the greater the freezing rate in the early stage and then slows down.When the freezing temperature is below-5℃,the frozen soil specimen is completely frozen at 20 h.When the freezing temperature is below-5℃,the specimen is still not frozen after 24 h.The compressive strength,elastic modulus and tensile strength of frozen soil increased gradually with the decrease of freezing temperature,and the maximum are 5.34 MPa,243.77 MPa and 2.00 MPa at-12℃;The shear strength,the internal friction angle and the cohesive force are both lower in the ice-water mixture state,higher in the non-freezing and complete freezing stage,and the maximum at-12℃are 654.98 k Pa,57.19 ° and 34.62 k Pa,respectively.Finally,based on Chapman-Jouguet theory and discrete element particle contact principle,the breaking process of surface frozen layer of open-pit mine in plateau cold region under blasting load is numerically analyzed by using particle flow discrete element software.The results show that at the moment of explosive charge explosion,cracks occur between the upper flat plate and the bench slope,and then uplift occurs.The increase of the thickness of the surface frozen layer will reduce the uplift height and increase the fragmentation of the frozen layer.The arrangement scheme of double-row blasting holes can reduce the fragmentation of the frozen layer;In the process of open-air bench failure,the higher the impact pressure and transverse and longitudinal velocity of particles in the frozen layer near the blasting center of blasting hole at the same horizontal height,the higher the transverse velocity of particles near the free surface of upper flat plate in the same vertical direction,the higher the longitudinal velocity of debris near the right free surface in double-row blasting holes,the earlier the increase time of the longitudinal velocity of debris near the right free surface,the first peak of impact pressure near the right free surface,and the higher the peak value of impact pressure near the frozen layer near the right free surface The theoretical calculation value of critical fracture length of open-air bench with single and double frozen layers and single blasting hole is 0.25 m 0.44 m,and the simulated measurement value is 0.32 m 0.51 m,respectively.After blasting,the lump rate of open-air bench with double frozen layers is 16.5% and 10.9% higher than that of open-air bench with single frozen layer,respectively.