Study On Blast-induced Degradation Law Of Rock Static Properties

Drill and blast method,D&B is the most common construction method for rock mass excavation.However,the blasting impact will form an excavation damage zone in the surrounding rocks in underground engineering,thus reducing long term stability of the construction.Study on blast-induced degradation law of rock static properties can provide theoretical basis for accurate evaluation of rock dynamic damage caused by blasting impact.It is of great practical significance to the stability and safety evaluation of surrounding rock in underground engineering construction by drilling and blasting method.In this paper,blast-induced degradation law of rock static properties was studied by the rock mechanics test in the research object of sandstone specimen subjected to predamage of blast impact.On this basis,the static and dynamic excavation of deep tunnel was simulated by FLAC3 D software.And the influence of the buried depth and later-al pressure coefficient on the evolution characteristic of surrounding rock displacement,stress and plastic zone distribution were analyzed.The main research results are as follows:(1)Compressional Wave Velocity test and uniaxial compression test results show that with the increase of blast center distance,the macro physical and mechanical parameters of samples like longitudinal wave velocity,uniaxial compression strength,elasticity modulus and characteristic stress present a strengthening trend of positive exponent and power function,but the rate of change decreases gradually;the deformation characteristic evolves from ductility to brittleness and the failure mode changes from compression and shear failure to tensile failure.On the premise that the blast center distance is constant,the increase of explosive quality means the increase of impact energy,the rise of dynamic damage degree of samples is embodied as the decrease of macro physical and mechanical par-ameters and the increase of fracture degree.(2)Brazilian split test results show that with the increase of blast center distance,the tensile strength of sandstone presents index is power function strengthen the trend,but its rate of change gradually decreased;Sandstone macro tensile mechanical behaveior has significant effect of strain rate,embodied in tensile strength and loading rate of the nature of numerical linear correlation,broken degree increased significantly with the increase of loading rate.(3)Triaxial compression test results show that with the increase of blast center distance,the triaxial compressive strength,elasticity modulus,internal friction angle and cohesion of samples present a strengthening trend of power function,but poisson ratio presents a weakening trend of power function,and peak strain increases gradually but relatively scattered,the macro mechanical parameters of samples with the same blast center distance increases with the increase of confining pressure.AE activity of the samples becomes lag with the increase of blast center distance,and the more smal-ler blast center distance is,the more strongly AE activity of the samples is.With the increase of blast center distance,the brittle deformation characteristic of samples is continuously strengthened,and the failure mode changes from tensile failure to tens-ion and shear failure and further evolves shear failure.(4)Based on the results of laboratory tests,the finite element model of deep tunnel was established,and the damage of surrounding rock after static and dynamic excavation was studied.The displacement,stress and plastic zone distribution evolutionary characteristics of tunnel surrounding rock under different buried depth and lateral pressure coefficient were revealed.