Blast-Induced Damage And Dynamic Responses Of Rock Near Active Fault Subjected To In-Situ Stress

Today,drill and blast method is still widely used in engineering rock mass excavation and other fields.Improper design of blasting parameters may lead to over excavation and under excavation of underground engineering rock mass,and even lead to instability of surrounding rock,causing serious safety accidents and economic losses.In addition,under high strain rate conditions,such as being disturbed by explosion or impact,the mechanical properties of rock will significantly change compared to quasi static conditions.Therefore,the dynamic mechanical response of rock materials under explosion and impact has been widely concerned by academic and engineering communities.The western part of China is one of the most active geological and tectonic regions in the world,and the frequent geological and tectonic movements have created a large number of fault zones,many of which are still active since the Quaternary period,causing a great impact on the construction of infrastructure such as transportation,water conservancy and energy exploitation in the western region.A railway in southwestern China,the construction of which has already started,is deeply affected by active faults,with more than 50 active faults along its route,which is rare in the world for its dense distribution and frequent activities.In addition,the railway confronts high mountains and deep valleys along the route,and the terrain has huge ups and downs,and many tunnels are facing the negative impact caused by large burial depth and high in-situ stress.Under the unfavorable conditions such as high in-situ stress and fault zone misalignment,the blast-induced damage the rock differs greatly from that under conventional conditions.Therefore,an in-depth study of the damage mechanism and dynamic response characteristics of the active fault rock mass under the coupling effect of ground stress and blasting,and revealing the mechanical properties of the rock mass in the fault zone under dynamic loading conditions,are of great significance to ensure the safe construction and operation of the projects in the active fault areas.In this study,based on the railway tunnel,theoretical research,numerical calculations and dynamic mechanical tests are conducted to study the influence of high in-situ stress,fault misalignment and other factors on the blasting damage mechanism and dynamic mechanical responses of the active fault rock mass,and the mechanical properties of the rock mass in the fault zone under dynamic loading were further investigated.The main contents are as follows:(1)Based on a dynamic finite element program,a numerical model of active fault rock mass blasting was established.The RHT constitutive model was used to simulate the rock mass in the affected area.The propagation process of blasting stress waves,equivalent stress,and principal stress evolution characteristics of active fault and rock mass in the affected area under different in-situ stress conditions were studied,and the two-dimensional and three-dimensional damage evolution mechanisms of rock mass in the fault affected area were revealed.The influence of fault dislocation on the dynamic mechanical response of active fault rock mass is analyzed.(2)In order to analyze the damage and mechanical response characteristics of fractured rock masses under dynamic loads,impact tests were conducted on rock samples with sandwich structures.Rock samples containing ordinary cement mortar,foam cement mortar and asphalt cement mortar as filling interlayer were prepared respectively.Split Hopkinson Pressure Bar tests were carried out on the samples under different loading strain rates.The influence mechanism of impact strain rate and interlayer material type on the dynamic strength,energy evolution and failure mode of the samples was analyzed.(3)Based on Weibull distribution and D-P strength criterion,a dynamic damage constitutive model of rock suitable for one-dimensional impact testing was established.The parameters of the constitutive model were taken based on the experimental stress-strain relationship,revealing the overall damage process of the sample,and the initial damage coefficient and damage rate were proposed to evaluate the damage process of the sample.The numerical calculation of blasting and impact tests was carried out based on the actual working conditions of the tunnel,revealing the evolution process of rock mass damage at different distances from the blast hole.