Experimental Study On The Effect Of Stress Level And Holdup Time On Using Kaiser Effect And DRA Method To Measure Granite Prestress

Acoustic emission Kaiser effect method as one of the methods for measuring ground stress,due to its simple,high-efficiency and low-cost features,it is increasingly valued by scholars at home and abroad.A lot of research has been done at home and abroad,but there are still many issues that have not been explained clearly.Which includes the effect of stress levels and holdup times on the Kaiser effect.It is difficult to accurately quantify the ground stress of natural rock,in this thesis,an artificial stress is applied to the rock instead of the ground stress to study the effect of the stress level and the holdup time on the Kaiser effect.At the same time,Deformation Rate Analysis(DRA)is also one of the methods for measuring ground stress,there are some studies abroad,but domestic research is still shallow.Mechanistically,there are many similarities between the DRA method and the Kaiser effect method.Therefore,the DRA method and Kaiser effect method are used to measure the pre-stress of rock,and the effect of stress level and holdup time has been studied.This thesis takes granite as the test object,Under precondition of different pre-stress and different retention time.Simultaneous measurement of prestress using Kaiser Effect method and DRA method.The particle flow software PFC was used to numerically simulate the Kaiser effect method and DRA method under different stress levels.The main work and conclusions are as follows:(1)A test system was established to simultaneously measure the pre-stress of the same rock samples using the Kaiser effect method and the DRA method simultaneously,which saves time and reduces costs.At the same time,the comparability of the test results obtained by the two test methods is enhanced,and the experimental errors caused by the differences between the different test pieces are eliminated.(2)The Kaiser effect method has very high measurement accuracy at each stress level;At the same time,the Kaiser effect during cyclic loading is not accurate,and the Kaiser effect after the preloading has high measurement accuracy,which indicates that the holdup time has a positive influence on the Kaiser effect.(3)The accuracy of the DRA method measurement is low in the low stress level,but it increases significantly with the increase of the initial stress value;There are successful specimens within each stress level,indicating that rock strain memory persists during crack closure.At the same time,there is a more positive effect when the load is preserved at low stress levels,and with the increase of the retention time,the greater the impact.However,when the stress level is high,the load has almost no effect and can be ignored.(4)Numerical simulation results show that the Kaiser effect and the DRA method are not based on the generation and propagation of cracks at low stress levels.At this point the rock is still in the crack closure stage,so the mechanism of the Kaiser effect and the DRA method is based on crack closure at low stress levels.When the stress level is high,the mechanism of Kaiser effect and DRA method is based on the generation and expansion of cracks.