Study On Specific Charge And Fragments Size Distribution In High-Strength Boulder Blasting

With the development of economic and the urbanization,the metro are being built in most of the big cities in order to meet people’s demands for the transportation.However,there are many challenges for metro construction because of the different and complex geological conditions.Such as,weathering spherical boulder is one of the complex geological conditions which are mainly in the south-east of China.In order to solve this problem,the drilling and blasting from the ground is applied to precondition the high-strength boulders.In this method,the fragments size after blast must be suitable for the haulage system of the TBM(Tunnel Boring Machine)machine.However,the specific charge in the blast is determined by some empirical formulas and there are few researches about the fragments size distribution.Therefore,the specific charge and the fragments size distribution are the problems which should be solved in metro construction.(1)Similarity criterion and the model test are designed based on the theory of similarity.UCS of boulders with 80MPa and 100MPa are included in the model tests,and fragments after blast are collected and sieved.(2)Analyzed the model test data.When different strength test blocks were blasted,the influence regularity for different levels cumulative mass would be concluded in the influence of different unit consumption and buried depth conditions,the relationship between specific charge and explosives depth and the average blockiness after blasting of the test block was summarized.The results was compared with other scholars’.In addition,fractal theory was introduced to calculate the fractal dimension of different test conditions and established its relationship of specific charge and explosives depth.(3)A three-dimensional numerical calculation model of boulder blasting was established by means of finite element software ANSYS/DYNA.The blasting of 80MPa and 100MPa test blocks at 12g and 20g explosives and different buried depths was simulated.The stress values at different distances from the source was extracted.From the perspective of stress distribution,the influence of explosive charge and depth variation on blasting stress distribution was analyzed and compared with the test results.