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Experimental Investigation On Direction Independence Of Kaiser Effect On Rock Under Different Loading Methods

Posted on:2023-06-09Degree:MasterType:Thesis
Country:ChinaCandidate:Z H WangFull Text:PDF
GTID:2530307070988279Subject:Engineering
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With the rapid development of infrastructure and national defense construction in China,there are higher requirements for the development and utilization of deep underground space.The measurement of in-situ stress is of vital importance to the preliminary design of the project.However,the traditional in-situ stress measurement method has many shortcomings,such as site limitation,the high requirement on rock integrity and equipment,limited accuracy of measurement results,high cost,and so on.Kaiser effect acoustic emission method can be used for laboratory tests,and it is cheap and can be used for many tests,which has strong engineering significance.Since the exact direction of the maximum principal stress cannot be determined before the test,the Kaiser effect method can be used as a feasible and effective method to measure in-situ stress only after determining whether the Kaiser effect has direction independence and the critical Angle of direction independence under different conditions.In this paper,a variable Angle fixture that can be accurate to 1° was self-made and used in the Instron1346 test machine for the uniaxial compression test.The Brazilian splitting test was carried out on the MTS815 rock testing machine,and the PCI-2 acoustic emission monitoring device was used simultaneously for acoustic emission monitoring.The effects of different loading conditions on acoustic emission characteristics and direction independence characteristics of Kaiser effect of granite,red sandstone,and marble under uniaxial loading and splitting loading were studied.The independent critical angles of the Kaiser effect direction of three kinds of rocks under different conditions are obtained,and their evolution law is revealed,which provides an effective experimental basis and reference for different rocks to choose loading conditions in in-situ stress measurement.The main conclusions are as follows:(Ⅰ)In this paper,the Kaiser point identification method with strong subjectivity in previous studies is improved,acoustic emission signal is denoised by spectral analysis.And Origin software is used to identify acoustic emission characteristic curves based on the double tangent method.This method can identify Kaiser points accurately and provide reliable data support for further analysis and research.(Ⅱ)Under uniaxial compression,the critical Angle of the Kaiser effect is between 10° and 20°.(Ⅲ)A method to measure the maximum and minimum horizontal principal stress directions of rock by wave velocity has been proposed in previous studies.It can control the Angle between loading direction and maximum principal stress direction within 10° when the acoustic emission method is used to measure in-situ stress.Combined with the conclusions of this paper,the validity of the Kaiser effect method for insitu stress measurement is verified.(Ⅳ)In the uniaxial compression test,for the rock with many microfractures,the reduction of the initial stress level will reduce the recognition accuracy of Kaiser points under uniaxial compression and reduce the critical angle with the Kaiser effect.But the initial stress level has little effect on the critical Angle under splitting conditions.(Ⅴ)Under uniaxial compression,the critical Angle of direction independence of the Kaiser effect increases linearly in a small range with the increase of loading rate.(Ⅵ)Different rocks show different ae characteristics and direction independence of Kaiser effect under different loading conditions.In the Brazilian disc splitting test,the critical Angle of granite is 13°,that of red sandstone is 1°,and that of marble is above 60°.(Ⅶ)Under uniaxial compression,the Kaiser effect point occurs earlier with the increase of deflection Angle,while the Kaiser effect point does not change regularly with the increase of deflection angle in the Brazilian disc splitting test.
Keywords/Search Tags:In-situ stress measurement, Kaiser effect, Critical Angle of direction independence, Loading rate, Uniaxial compression, The Brazilian splitting test
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