| Through homogeneous sandstone and save this paper direct shear destruction of the whole process of rock structural surface acoustic emission theory and experiment to explore the short-term degradation and frequent(seismic)under the action of cyclic loading under the stress of rock mechanics features and acoustic emission parameters,multi-angle analysis of sandstone structure surface direct shear short degradation and peak before the shear rate in the process of cyclic loading,failure pattern and the cyclic loading frequency and amplitude on the influence of the parameters of acoustic emission characteristics,in order to establish a track loading process of rock mass based on the acoustic emission phenomenon along the original joint or structural plane shear characteristics changes provide theoretical basis for stability evaluation method.The main research contents and conclusions of this paper are as follows:1.Conventional direct shear tests show that the existence of sandstone structural plane weakens the shear strength of rock mass;The failure peak shear strength is different in different modes.Short-time deterioration and cyclic shear direct shear tests show that,regardless of the presence or absence of structural surface,with the increase of cyclic loading rate and cyclic loading amplitude,the shear strength of joints decreases,and the damage and deterioration of joints caused by prepeak cyclic loading become more obvious.Cyclic loading of finite number of times is beneficial to the peak shear strength of joints.2.Based on the principle of damage and acoustic emission of engineering rock structural surface,short-time degradation tests of rock mass in direct shear were conducted under different failure modes and shear rates to study acoustic emission characteristics of sandstone structural surface.The results show that:(1)under the same failure mode,as the shear rate increases,the ae ringing count rate,energy rate,impact rate,cumulative ringing count,cumulative energy and cumulative impact number decrease successively;(2)at the same shear rate,the order of ringing count rate and energy rate peak value at the moment of failure is the same,and the cumulative number of impacts decreases successively with the failure mode of rock mass from climbing failure to climbing--gnawing failure and then to gnawing failure.3.Based on the conventional direct shear test and short-time degradation direct shear acoustic emission test,the acoustic emission characteristics of homogeneous sandstone and rock mass with structural surface in the process of cyclic loading and unloading are analyzed from three aspects of cycle times,amplitude and rate.The results show that:(1)the cyclic loading of a limited number of times is beneficial to acoustic emission signal,and the ae ringing count,energy and impact number decrease with the increase of cyclic loading times and loading amplitude.(2)the peak cyclic shear amplitude had little influence on the change trend of AE signal,but the AE signal was stronger and the cumulative curve slope was higher when 0.8fs was applied.(3)Kaiser effect is in the majority when 0.8Fs;With 0.5Fs,Kaiser effect decreases and Felicity effect increases.(4)except for the failure mode of climbing and gnawing,the cumulative number of impacts decreases with the increase of shear rate;In addition to the failure mode of climbing,the cumulative ringing count and accumulated energy were both the maximum and minimum values when the shear rate was 1.0kn/s and 1.5kn/s respectively.4.As a precursor of acoustic emission monitoring of rock mass disasters,relative quiet period is the key to the prediction of rock mass instability.Acoustic emission impact(ae)can characterize the damage changes inside the specimen and be used to judge and predict whether the rock mass has shear failure or not.Felicity ratio can be used to characterize the degree of internal damage of rock mass.The combination of these characteristics in the process of rock mass failure can be used as the cr:iterion for rock mass failure. |
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