| In engineering construction,the stability of rock mass is closely related to the safety and reliability of engineering.Therefore,understanding the mechanical properties of rock mass in construction environment is an important prerequisite for engineering construction.The mechanical properties of rock mass are greatly affected by layered structures,and the distribution of rock mass with layered structures is very wide,Therefore,if only considering lithology and neglecting the variation of bedding dip Angle,it will bring great risks to the smooth operation of engineering.it is necessary to carry out research on the change of bedding Angle and the change of rock failure mode and mechanical properties.By selecting vertical bedding,horizontal bedding and 45°bedding soft rock(phyllite)and hard rock(slates)to carry out uniaxial compression test,combined with acoustic emission technology to carry out whole-process monitoring,Based on the experimental data,the influences of bedding Angle on the failure mode,mechanical properties and acoustic emission characteristics of soft and hard rock were investigated.After analyzing the experimental results,the conclusions are as follows:(1)Based on the analysis of the development of cracks after failure,the fracture mechanism of layered soft and hard rock with vertical dip Angle is splitting failure,the fracture mechanism of layered soft rock with horizontal and 45°Angle is shear failure,and the fracture mechanism of layered hard rock with horizontal and 45°dip Angle is mixed failure of splitting and shear.(2)The AE Ra value can determine the timing characteristics of crack development when the crack mechanism is mixed failure,and It is found that the shear crack first develops and then the splitting crack expands.Acoustic emission ringing count reflects the inoculation and development of the internal cracks in the rock sample.The time of main crack initiation in hard rock is before the peak compressive strength of rock sample,while The time of main crack initiation in soft rock is after the peak compressive strength of rock sample.The AE energy is the elastic energy released by the AE source,and the way of crack initiation and propagation affects the AE energy release.The failure mode of rock samples is shear failure,with less AE energy released,while the failure mode is splitting failure,with a large amount of AE energy released instantly.Acoustic emission parameters can determine the cracking state of faulted rock and provide early warning signal of fracture.Ringing count and energy surge are early warning signals.When this signal occurs,it indicates that the failure of hard rock is about to occur,while for soft rock,it indicates that the elastic stage is about to enter the plastic stage.(3)Combined with the failure characteristics of rock samples and acoustic emission characteristics,it can be inferred that the failure mechanism of soft rock is lattice slip followed by lattice fracture leading to final failure,while the failure mechanism of hard rock is only caused by lattice fracture.Source localization is an important purpose of acoustic emission technology,which can roughly describe the damage area inside the material.In this paper,the location method of acoustic emission source for layered rock is explored.Snell's theorem is used to derive travel time equations of AE source propagating in two dimensional plane in two layers and three layers,and the travel time equations are solved by particle swarm optimization algorithm,The source location in the single-velocity model and the multi-velocity model considering the layered structure are obtained respectively,and the difference of positioning accuracy in the two cases is compared.At the same time,the influence of the speed selection value on the location accuracy of the source in the single velocity model is investigated. |
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