| With the rapid development of mining engineering and the requirement of underground engineering,the situ rock stress measurement is more and more important in the mining and geotechnical engineering.Nowadays,the cost of measurement methods of the situ rock stress widely used is relatively high,the method of acoustic emission Kaiser effect because of the testing cost is lower,so it is taken more and more seriously at home and abroad.Kaiser effect of acounstic emission method opens up a new way for measuring the situ rock stress.There are still some problems have not been resolved although this method has many advantages,such as stress level,temperature,humidity,and the maximum principal stress of rock specimen sampling angle on the Kaiser effect of the influence on the accuracy of the in-situ stress measurement,the uncertainty of these factors hinder the promotion of the method.Among them,the loading direction and the principal stress direction with a certain angle,the existence of the Kaiser effect and measurement accuracy directly affect the reliability of test results.This thesis regards sandstone in Chongqing area as the research object,using the WAW-1000 type electro-hydraulic servo test system and PCI-2 full digital acoustic emission signal acquisition system producted by PAC company.And use the two equipments to test the four disk specimens(complete,containing a precast crack,two precast cracks and four precast cracks)under the surrounding angle of 60°,30° and 10°,the tests was performed in the four disk specimens loaded in two cycles with rotation of 50,10°,15°,35°and 60°.With analyze the acoustic emission characteristics of experimental conditions and the propagation of the cracks when test specimens were broken.The main results are as follows:? Using the basic knowledge of fracture mechanics to calculate stress intensity factor in the disk model containing a center single crack and a population of cracks,and find that:1)For a single crack model,when the loading angleyis constant,with the increase of the angle(?0)between the crack surface and the loading direction,the value of stress intensity factor K?*decreased gradually,the value of stress intensity factor K?*increased gradually.For the angle(?0)between the crack surface and the loading direction is constant,with the increase of the loading angley,the stress intensity factor K?*and K?*decreased.2)For the model with multiple cracks,with the increase of damage variable D,the stress intensity factor of crack tip is decreased nonlinearly.And with less crack in the specimen,the crack stress of the wing type is smaller.? Using the arc loading,the four disk specimens(complete,containing a precast crack,containing two precast cracks and containing four precast cracks)under the surrounding angle of 60°,30° and 10°,the tests was performed in the four disk specimens loaded in two cycles with rotation of 50° 10°,15°,35°and 60°.And research the Kaiser Effect of the four specimens in the test.Through the way of arc loading,the loading direction can either deflection angle in the disk test.The results are as follows:1)Based on the study of the test about the same surrounding angle under different deflection angle,and find that:the accumulation of AE energy curves of the second direction has a memory of the loads of first direction in a big range of rotation angles in the scope of 0°?60°,but with the angles bettwen cycles loads increased,the Kaiser Effect turns to be not clear.2)Different specimens under the same surrounding angle,the arrangement of breaking load value from big to small goes:complete specimen,containing a precast crack specimen,contains two precast cracks specimen,contains four precast cracks sample.3)The same specimen under different surrounding angle,AE count rate and the cumulative number of acoustic emission from big to small goes:60° surrounding angle,30° surrounding angle,10° surrounding angle.? Describing the order of micro-cracks appeared on the tip of pre-existing cracks.Analyzing the expansion of new cracks and the failure modes of the specimens which containing two precast cracks and containing four precast cracks under different surrounding angle.Considering the impacts of the space arrangement factors of cracks on the initiational mode and failure mode,as follows:Under surrounding angle 60°,the failure mode of specimens is shear failure;Under surrounding angle 30° and 10°,the failure mode of specimens contain:tenso-shear compound damage,the wing type crack and the precast cracks cut-through damage.With the decrease of the block surrounded angle,damage close to the splitting test.? Using the finite element software ADINA to esTablelish the disk model under the condition of the arc loading.We simulate the four kinds of specimens(complete,containing a precast crack,containing two precast cracks and containing four precast cracks)with disk rotation in 10°,30°,600° surrounded by three different angles respectively,and get the distribution of the stress state.Through analyzing the stress distribution and the failure mode of the specimens,get they are influenced by the surrounding angle,the number of precast cracks in specimens and the position of the crack in the specimens. |
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