Acoustic Emission Characteristics And Warning Model Of Slope Instability Based On The Active Waveguide

In China,the landform is quite complex and the climate is changeable,so the landslides disasters often occur with greater destructiveness,which is one of the geological disasters with most serious impact.Influenced by many factors,the comprehensive action causes the diversity mechanisms of slopes instability failure,which makes serious difficulty and challenge to the monitoring and warning work.Therefore,how to realize the effective correlation between the early warning information and the slope instability failure,and to accurately identify various deformation states during the slope failure process,thus it is the key research to improve early warning level at present.It is of great practical significance to study the scientific method to obtain the warning information,and to establish the effective connection between the precursor information and the slope instability state.Many scholars have carried out many research on acoustic emission(AE)monitoring in slope engineering,and some achievements have been achieved.In recent years,the AE monitoring technology based on the active waveguide structure has been widely concerned,while the relevant research is still in the exploratory stage.In view of the AE monitoring characteristics of the active waveguide technology,the prediction method is required further study to improve the identification reliability of slope internal deformation by the effective AE parameter indexes,which can further improve the prediction reliability of slope failure,to provide relevant reference for the future engineering application.Based on the AE monitoring method with the active waveguide structure,the monitoring principles for the soil slope and rock slope were clarified respectively,and the physical tests were designed accordingly to investigate AE characteristics under sliding deformation,tensile loading and shear loading conditions.Besides the correlations between AE statistics count and displacement,loading rates and displacement rates were further studied.The macro and micro analysis of AE characteristic was carried out based on the FLAC-PFC coupled model,to reveal the AE mechanism,AE distribution pattern and magnitude of AE slip/microcrack events during the slope failure process.Then,the warning intervals were investigated based on the mutation analysis of high-frequency and cumulative AE count,further the multi-level warning model of slope instability failure was proposed.The main conclusions are as follows:(1)The progressive,sudden and steady sliding deformation tests were implemented based on the active waveguide structure,respectively.Based on the evolution characteristics of AE count,parameters correlation,signal time-frequency and energy percentage,the recognition methods of deformation state,deformation pattern and precursor characteristic were explored based on the AE parameter indexes.The results show that the curves have cumulative AE count has prominent consistency between the cumulative AE count and sliding deformation,and the AE statistical count has a good quantitative relationship with the sliding displacement.There is a specific time-frequency distribution during sliding deformation process,it’s found that continuous high-frequency signals appear in the accelerating deformation stage,and the percentage of high-frequency band energy remains at a relatively high level.The time-frequency characteristic is a suitable criterion to identify the sliding deformation stage,which has obvious precursory recognition feature.(2)Based on the mechanical principle of active waveguide structure for the rock slopes,the tensile,shear and periodic loading tests of mortar specimens with waveguide were carried out.The results show that with the tensile loading increase,AE count,amplitude and energy begin to increase gradually,and the signals in the correlation diagram show expanding trend gradually.Then,the continuous high-frequency signals begin to appear.Near the peak state of tensile stress,the AE signals increase sharply with the amplitude ranging from 40～90 d B.Besides a large number of high-frequency signals appear in the 300～400 k Hz dominant frequency band,and the energy percentage of high-frequency band fluctuates in the 30%～35% high-level range.Through a series of tensile loading tests(0.1～1.0 k N/s),it is found that AE statistical count is quite sensitive to the loading rates,which can greatly judge the loading state and evolution trend of tensile fracture,providing reference for discriminating the expansion state of the dangerous rock mass.(3)Under the shear loading process,the activity level of AE events gradually increase,and then the distribution range of AE signals dominant frequency gradually expands with continuous high-frequency signals.Close to the failure stage,the signals high-frequency domain is mainly concentrated between 350～450 k Hz,and the energy amplitude of high-frequency band is relatively high.Then,the AE statistical count begins to show a significant downward trend.Notably,the relationship curve between AE statistical count and shear displacement shows the downward trend of “falling back”,and the relationship curve of AE statistical count and shear stress shows the evolution trend of “hook back”.What’s more,with the cyclic times increase,the high-frequency signals do not appear in the late cyclic stage,and the signals frequency domain is mainly distributed in the range below 200 k Hz.The energy percentage of high-frequency band gradually decreases and then increases,at a larger value during the final damage stage,reaching up to 30%～35%.In addition,the shear loading tests show that there is a high quantitative relationship between the shear displacement rates(0.25～1.50 mm/min)and the AE statistical count,which can be probable to calculate the slope displacement rate by effective quantitative indicators.(4)Based on FLAC/PFC coupled model,the progressive landslide and dangerous rock collapse numerical models were established,and the macro and micro analysis of AE characteristics between the source particles during slope failure process was carried out.The AE events simulation method between source particles was established based on moment tensor theory,and the AE mechanism,AE distribution pattern and magnitude of AE slip/microcrack events were investigated.The simulation results show that the activity level of AE events,the AE count percentage and the magnitude of AE slip events show distinct increase trend in the accelerating deformation stage,and AE events are mainly distributed along the sliding zone.In the unstable process of dangerous rock mass,near the formation period of macroscopic fracture,a large number of micro-cracks among the discrete particles begin to concentrate in the region close to macroscopic fracture.The magnitude of AE microcrack events increase significantly,there is the approximate normal distribution relation between the events number and magnitude of AE microcrack events.Then,the number of micro-cracks gradually decreases,indicating that the internal macroscopic fracture has formed inside the rock slope.(5)By the sliding deformation,tension and shear loading tests of the active waveguide structure,it is found that the AE signals dominant frequency domain firstly appears the mutational high-frequency band,and then the gray and catastrophe model of the cumulative AE count shows the mutation characteristic.Thus,the warning boundary conditions are established based on grey and cusp catastrophe theory with the cumulative AE count,considering the mutation characteristics of the AE signals dominant frequency,the AE warning intervals are built.Based on the AE warning intervals,the multi-level warning model for slope instability failure is further proposed considering the evolution trend of AE signals identification indexes comprehensively,which can provide some reference for the slope monitoring and warning research based on the AE monitoring technology.