| In the western mining areas of China,the shaft passes through the cretaceous water-rich bedrock,which is relatively late diagenesis and has the characteristics of low strength,weak cementation,many pores and cementing..Therefore,the freezing method is often used to block groundwater and improve the stability of surrounding rock.In the process of blasting excavation,the frozen wall is often damaged and cracked by impact loading,lead to engineering accident and delay the construction period,which is mainly due to the insufficientcognition on the mechanical behavior of these strata.Rock tensile strength is far lower than the compressive strength,and tensile failure is the main failure mode under the impact loading.Therefore,in this paper,SHPB system is used to conduct dynamic Brazilian disc splitting tests on this strata rocks at different freezing temperatures.The research and analysis are carried out from three aspects:mechanical properties,constitutive relations and numerical simulation.The main research work and conclusions are as follows:(1)On-site sampling and processing of typical Cretaceous strata,and then the dynamic splitting test of frozen sandstone under different strain rate and different temperature were carried out by using the split Hopkinson pressure bar equipment and low temperature freezing test chamber.The strain rate effect and temperature effect of mechanical parameters such as stress-strain curve characteristic,peak strength and tensile modulus of frozen sandstone are analyzed and discussed.The results show that the dynamic peak strength and peak strain of frozen sandstone have obvious strain rate effect and temperature effect,while the tensile modulus shows strain rate independence and temperature dependence.(2)According to the dynamic splitting results of frozen sandstone,the relationship between the energy dissipation mechanism,failure mode and freezing temperature,strain rate of frozen sandstone under the shock load were systemically studied.The relationship between the dynamic stress increase factor and strain rate was obtain by combing the static parameters.The crack propagation mechanism of samples in the failure process was analyzed by using high-speed photography technology,and the dynamic splitting critical failure thresholds of frozen sandstone at the test temperature were determined.(3)By introducing the ice particles reinforced theory and interface debonding damage theory,the constitutive relation of frozen sandstone under the impact load is characterized.Combined with the statistical damage theory,the viscoelastic and overstress constitutive models are improved,and the dynamic damage constitutive model of frozen sandstone are obtained,and the constitutive parameters were determined and the influence analysis were made.It has been proved that the obtained constitutive curves are in good agreement with the experimental curves,and the constitutive model is suitable for the characterization of the dynamic splitting mechanical behavior of frozen sandstone.(4)According to the dynamic splitting experimental results of frozen sandstone,ANSYS/LS-DYNA software was used to conduct numerical simulation analysis,and the parameters of HJC constitutive model under the test temperature were determined.The effects of loading strain rate and freezing temperature on dynamic crack growth of frozen sandstone were studied,and the stress distribution and propagation process of the samples under different working conditions were analyzed.In this paper,based on laboratory tests,the dynamic splitting mechanical behavior,constitutive model and numerical application of frozen sandstone are systematically studied combing with theoretical analysis and numerical simulation.The understanding of dynamic mechanical properties of this kind of rock is supplemented and improved,which provides basic parameters and basis for engineering problems such as blasting parameter design and support optimization in vertical shaft freezing construction in western mining area. |
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