Experimental Study On Acoustic Emission Of Plagiogranite Under The Unloading Confining Pressure Path

During the preliminary investigation of the Yebatan Hydropower Station in the upper reaches of the Jinsha River,a unique geological phenomenon was revealed,namely the phenomenon of ?deep rupture? or ?deep unloading?.This geological phenomenon restricts the operation and maintenance of the project to a certain extent,and at the same time it restricts the development and innovation of the project construction,which leads to additional investment and extension of the construction period,and brings huge challenges to the water conservancy and hydropower project.After comprehensive consideration of the actual situation of the site and the laws of river valley evolution,a three-axis unloading test in line with the actual engineering conditions in the dam site was designed.This test is in line with the evolution of the river valleys.At the same time,the tunnel excavation in the deep mines Mining and high slopes are equally applicable.In this paper,the MTS815 rock mechanics tester and PCI-II acoustic emission test system were used to test the acoustic emission of plagiogranite under the unloading confining pressure path.The following results were obtained:(1)According to the change law of the ringing count and energy count of the acoustic emission,the rock instability and destruction process can be divided into four stages: acoustic emission silence stage,relatively stable stage,steady growth stage and accelerated transition stage.The four stages of division can better correspond to the rock instability phase.Meanwhile,water can change the acoustic emission time structure of the entire rock instability and destruction process,that is,prolong the time of relatively stable stage and reduce the time of steady growth stage.(2)Based on the temporal and spatial distribution of acoustic emission events,a new method to discriminate the precursors of rock instability is proposed,namely the non-uniform coefficient method.The inhomogeneous coefficient of the entire rock instability process generally shows the trend of ?level-decrease-transition?,which reflects to a certain extent that the internal crack propagation of the rock is an evolutionary process.When the failure is approaching,the heterogeneity appears large.The transition is approaching 2,so the non-uniform coefficient can be reached(approach)2 as an important measure to determine rock failure.(3)Based on the variation law of acoustic emission(RA)values,the process of rock instability is the process of gradual increase of shear cracks to form a macroscopic rupture surface.The shear fractures of saturated samples are lagging in time,and the effect of water restricts the rock.The acoustic emission intensity weakens the rock's ability to resist deformation and promotes brittle to ductile granite.(4)Based on the dissipation theory,the change of acoustic emission energy under accelerated energy release(AER)is discussed.The r-value and z-value are both less than 1,indicating that the accelerated release of energy during the destabilization and failure process of granite unloading confining pressure path is obvious.Based on acoustic emission parameters,a rockburst criterion based on r-value is established,and a new idea is pointed out for judging rockburst.(5)In combination with acoustic emission parameters,a comprehensive integrated criterion of rockburst based on lithological conditions,acoustic emission parameters,surrounding rock conditions,and hydrological conditions was established.Taking the Yebatan example as an example,the comprehensive integration criteria established have been demonstrated,which verifies the accuracy and applicability of the integrated integration criterion.