| The in-situ stress,also known as the original rock stress,refers to the inherent stress state of a point in the rock and soil,which is the necessary foundation for the scientific design and safe conetruction of geotechnical engineering.At present,there are hydraulic fracturing and stress relief methods in common use at home and abroad,but they are limited by poor measuring conditions and high cost.Using Kaiser effect of rock material,acoustic emission method is used to directly measure borehole core.However,there are still some problems in this method,such as the choice of loading mode and factors influencing Kaiser effect,which need further study.To this end,this paper uses the RMT-100B rock mechanics servo testing machine and the American Physical Acoustics Company's Micro-? Express acoustic emission monitoring system to carry out equal amplitude cyclic loading and unloading and graded loading and unloading cyclic tests under different cyclic stress levels for granite,sandstone and gneiss.The main research contents and conclusions are as follows:(1)This paper deeply analyzes the stress-time-acoustic emission parameter curve characteristics of three typical rocks under different cyclic stress levels and cyclic loading and unloading conditions,and the effect of cyclic loading on the Kaiser effect.The results show that the Kaiser effect of all three rocks occurs between 10%and 20%of the peak intensity;When ?ci<the previous maximum stress ?mk,the cyclic loading can make the rock specimens pass through the compaction stage,effectively reducing the occurrence of friction-type acoustic emission phenomena;when ?ci>?mk,the cumulative ringing curve curve rises in steps,and the interior of the rock When crack growth occurs or a new crack develops,the cyclic stress becomes a new memory stress.(2)In this paper,the felicity ratio is used to measure the effectiveness of Kaiser effect,and a method of cyclic loading and Kaiser point identification for accurate measurement of in-situ stress is proposed.The results show that at that time,the felicity ratio is less than 1,on the contrary,it is greater than 1,which can be used to narrow the identification range of Kaiser effect points;therefore,when using the acoustic emission method to measure the in-situ stress,the Kaiser points can be accurately picked up by using small gradient,graded cyclic loading method,and combining with felicity ratio(3)According to JCMS-IIIb5706(2003)acoustic emission parameter analysis method,a series of dynamic evolution,such as the generation and expansion of micro fracture of three typical rocks,is revealed under the condition of graded cyclic loading and unloading The results show that the tensile failure is the main feature of the three kinds of rocks with more AF and less RA at the early stage of loading,and the shear failure is the main feature of the rocks with more AF and less RA at the later stage of loading(4)In this paper,the core of Yungaishan is selected,combined with the experimental research,the small gradient,graded cyclic loading and unloading scheme is designed for engineering application,and the picking range is further reduced by using felicity ratio,which is found to effectively improve the reliability of the stress test results. |
PDF Full Text Request