Study On Acoustic Thermal Response Characteristics Of Water Bearing Sandstone Under Cyclic Loading

During the coal mining process,there are many coal bodies that they are not only affected by crustal stress,but also by repeated disturbance of various projects and long-term water erosion.All these aggravate their damage accumulation and even damage instability.In the process of damage and failure of coal and rock mass,it is released that acoustic emission energy and infrared radiation energy.In order to study the damage evolution law of sandstone in the process of instability and failure,it is designed that the cyclic loading test of water bearing sandstone in this paper.At the same time,the acoustic emission method and infrared radiation method are used for joint monitoring.The damage evolution model of sandstone is established by analyzing the variation characteristics of acoustic emission parameters,infrared radiation parameters and strength of Sandstone during cyclic loading.And the damage evolution characteristics of sandstone during cyclic loading are obtained.Based on the "acoustic thermal" response information characteristics of different water bearing States,the influence of water erosion on the damage degree of sandstone is studied.The main conclusions are as follows:(1)The acoustic emission count rate of rock in water bearing state is obviously lower than that in dry state.During the compaction cycle and elastic cycle,the cumulative acoustic emission ringing count remains at a low value.The acoustic emission count rate during the first cycle of each stage is significantly higher than that in the subsequent cycle,and the acoustic emission count rate in the loading stage is higher than that in the unloading stage.In the plastic cycle stage,the ringing count rate increases and the average count rate of unloading section increases obviously.Before the failure and instability of the sample,the AE count rate obviously appears in the high value dense area.(2)The change trend of air in compaction cycle and elastic cycle has universal characteristics that the Average Infrared Radiation Temperature(AIRT)of loading section increases and unloading section decreases.The AIRT of dry rock samples is mainly of cooling type,while the AIRT of water bearing rock samples is mainly of heating type.However,the change range of air in water state is smaller than that in dry state.Before the failure and instability of the specimen,the change range of AIRT increases obviously.(3)The Variance of Successive Minus Infrared Image Temperature(VSMIIT)of rocks changes abruptly from the later stage of elastic cycle.And high temperature spots began to appear in the differential sequence thermal images,but there was no high temperature dense area.Before rock failure,the amplitude of VSMIIT mutation increases,and the high temperature intensive area appears in the differential sequence thermal image.(4)During the compaction and elastic cycles,the value of surface damage variable accumulates at a stable rate,and the surface fatigue damage accumulation is greater than that of internal fatigue damage.In the plastic cycle stage,the upper limit of cyclic stress of rock reaches more than 70% of the maximum stress,the internal damage variable increases greatly,and the fatigue damage accumulates rapidly,while the surface damage variable still increases slowly.There are 34 figures,9 tables and 88 references in this thesis.