Study On In-situ Stress Measurement By Kaiser Effect Of Rocks

The exploration of the natural stress state of the rock mass and the analysis of in-situ stress field are the necessary work for the investigation,feasibility demonstration,design and construction of the large-scale rock mass projects.There are field test methods and indoor test analysis methods to detect the natural stress of rock masses.Field test methods take time,labor,and cost investment.On the contrary,the indoor test analysis methods represented by rock Kaiser effect have unique advantages.However,the Kaiser effect test method for rock stress is still in the process of further development and improvement.Many theoretical and practical testing techniques and other issues need to be further discussed,supplemented and improved.Therefore,based on the Kaiser effect test data of five kinds of rock samples: fine sandstones,mid-grain dolomites,quartz sandstones,pagioclase ganites,and fine gabbros,further analysis is made on the Kaiser effect test data processing and analysis method for the in-situ stress.Enriching the content of related research,and promote the method to further improve and mature.The analysis and research works and the main results are as follow:(1)Using the scanning electron microscope observations and schistose-facies identification methods to test and analysis the above five kinds of rock mineral composition,structure and structural features,determine the fine microstructures and structures of the five kinds of rock,provide data for analyzing the mechanism of the Kaiser effect of rocks.(2)The acoustic emission characteristics of rock under cyclic loading and unloading under uniaxial compression are tested and analyzed.The acoustic emission characteristics of rock under this loading condition are obtained,that is,the initial stage of reloading,the acoustic emission activity of rock has a wave enhancement phenomenon.When the stress reaches the maximum stress value of the previous loading,the acoustic emission activity of rock is of great importance.The phenomenon of the dramatic increase is the Kaiser effect.(3)Using the acoustic emission data of rock cyclic loading test,the Felicity ratio of each rock sample was obtained,and the existence of Kaiser effect was verified quantitatively.The results show that when the applied stress is between 17% and 60% of the peak strength of the rock,the Felicity ratio of the rock is between 0.9 and 1.1.At this time,the Kaiser effect of the rock has a strong "memory ability" for historical stress.(4)In order to avoid the interference caused by the microfissures of rock sample development on the determination of Kaiser effect rock feature points,a method for comprehensively considering the characteristics of the time course curve of energy logarithmic cumulative counts and acoustic emission event counts of rock acoustic emission to determine the Kaiser effect feature points was proposed.This method improves the rationality of the Kaiser effect feature point determination.(5)Based on the theory of elastic mechanics and the calculation program of principal stress,on the basis of determining the multi-level Kaiser effect feature points of rock,a method of using combinatorial calculation to obtain the principal stress and its main direction under each combination was proposed.According to this,it is excluded that the in-situ stress of the rock mass can not be zero stress and negative stress,and further reference is made to the geological and neotectonic characteristics of the sampling area to determine the magnitude and direction of the in-situ stress at the test point.