【摘要】：針對(duì)不同地應(yīng)力異常區(qū)中小尺度采掘時(shí)加卸載導(dǎo)致的動(dòng)力災(zāi)害問(wèn)題,基于真三軸采動(dòng)煤巖體動(dòng)力顯現(xiàn)實(shí)驗(yàn)系統(tǒng),設(shè)計(jì)了能夠?qū)崿F(xiàn)實(shí)時(shí)監(jiān)測(cè)的真三軸聲發(fā)射監(jiān)測(cè)單元,并綜合采用實(shí)驗(yàn)室實(shí)驗(yàn)、理論分析等手段,對(duì)真三軸受載下煤樣力學(xué)性質(zhì)與失穩(wěn)破壞特征、聲發(fā)射規(guī)律以及微破裂、波速和時(shí)空演化規(guī)律進(jìn)行了系統(tǒng)探究。聲發(fā)射研究結(jié)果表明,真三軸受載煤樣振鈴計(jì)數(shù)受載荷水平、個(gè)體差異與加載速率影響。在低載荷水平下,由振鈴計(jì)數(shù)代表的煤樣損傷較多出現(xiàn)于加載階段,且數(shù)量較少。隨著載荷水平的增加,煤樣內(nèi)振鈴計(jì)數(shù)逐漸升高,保壓階段的振鈴計(jì)數(shù)也大幅增加,表明煤樣損傷過(guò)程逐漸由加載階段向保壓階段轉(zhuǎn)移。此外,在不同載荷水平下,煤樣內(nèi)聲發(fā)射事件主要集中于加載初期,而聲發(fā)射事件總量則隨著載荷水平的逐漸增加而具有先上升后下降的趨勢(shì)。在極高載荷水平下,聲發(fā)射事件極少并平均分布于整個(gè)加載階段。力學(xué)與失穩(wěn)破壞特征研究結(jié)果表明,真三軸中、低載荷受載煤樣在各方向均呈現(xiàn)出壓縮狀態(tài),但隨著最大主應(yīng)力與中間、最小主應(yīng)力逐漸增加,最小主應(yīng)力方向與中間主應(yīng)力方向相繼出現(xiàn)擴(kuò)容現(xiàn)象。在低載荷水平下,煤樣內(nèi)主要以張拉破裂為主,隨著載荷水平不斷增加,微破裂類(lèi)型逐漸轉(zhuǎn)變?yōu)榧羟衅屏?同時(shí)破裂數(shù)量在保壓階段的上升速度有明顯增加。在進(jìn)行單面自由狀態(tài)的三軸卸荷時(shí),低載荷受載煤樣因未達(dá)到承載極限,其外觀仍保持完整形態(tài)且無(wú)明顯動(dòng)態(tài)破壞發(fā)生,而高載荷受載煤樣因已達(dá)到承載極限而在內(nèi)部遭受二次損傷,其破壞以煤渣在自由面大量掉落的形式發(fā)生。微破裂、波速與能量演化規(guī)律研究結(jié)果表明,在真三軸加載初期,原生孔隙逐漸閉合與原生致密區(qū)的初始受載使此階段煤樣內(nèi)出現(xiàn)少量的高、低波速區(qū)。隨著載荷逐漸增加,原生孔隙壓實(shí)與致密區(qū)破裂造成高波速區(qū)轉(zhuǎn)移擴(kuò)展與波速異常區(qū)形成。煤樣接近破壞時(shí),宏觀裂隙的貫通使煤樣內(nèi)出現(xiàn)大面積低波速帶,內(nèi)部大量產(chǎn)生與閉合的裂隙使高波速區(qū)、波速異常區(qū)迅速變化轉(zhuǎn)移,煤樣已處于不穩(wěn)定狀態(tài)。在真三軸高載荷保壓階段,由于煤樣裂隙的不斷壓實(shí)與內(nèi)部結(jié)構(gòu)特征的充分破壞,煤樣內(nèi)出現(xiàn)以低波速區(qū)不斷減小與整體波速提高為代表的持續(xù)性損傷。此外,在真三軸加載階段,煤樣內(nèi)累計(jì)破裂釋放能量分布較為集中,其位置大致對(duì)應(yīng)高波速區(qū)與波速異常區(qū),同時(shí)極大值也不斷升高。當(dāng)煤樣失穩(wěn)破壞后,累計(jì)破裂釋放能量分布逐漸分散并貫穿整個(gè)試樣,其極大值增速卻趨于平緩。
[Abstract]:In order to solve the problem of dynamic disasters caused by loading and unloading in different geostress anomaly areas, a true triaxial acoustic emission monitoring unit is designed based on the real triaxial coal and rock dynamic behavior experimental system. By means of laboratory experiments and theoretical analysis, the mechanical properties and the characteristics of instability, acoustic emission, microfracture, wave velocity and space-time evolution of coal samples under true triaxial loading are studied systematically. The results of acoustic emission study show that the ringing count of true triaxial loaded coal samples is affected by loading level, individual difference and loading rate. At the low load level, the damage of coal samples represented by ringing count appears more in the loading stage and the quantity is less. With the increase of loading level, the ringing count of coal samples increases gradually, and the ringing count of the holding stage increases significantly, which indicates that the damage process of coal samples is gradually transferred from loading stage to holding pressure stage. In addition, under different loading levels, the acoustic emission events in coal samples are mainly concentrated at the initial loading stage, while the total acoustic emission events tend to rise first and then decrease with the increasing of load level. At extremely high load level, acoustic emission events are rarely and evenly distributed throughout the loading stage. The results of mechanical and unstable failure characteristics show that in the true triaxial, the low-load loaded coal samples show a compression state in all directions, but with the maximum principal stress and the middle, the minimum principal stress increases gradually. The minimum principal stress direction and the intermediate principal stress direction are expanded one after another. At the low load level, the tensile fracture is the main factor in the coal sample. With the increasing of the load level, the micro-fracture type gradually changes into shear fracture, and the amount of fracture increases obviously in the pressure keeping stage. When the triaxial unloading is carried out in one side free state, the low-load loaded coal sample does not reach the loading limit, and its appearance remains intact and has no obvious dynamic damage. The high load loaded coal samples suffer secondary damage in the interior because they have reached the loading limit, and the damage occurs in the form of a large amount of coal slag falling off the free surface. The results of microfracture, wave velocity and energy evolution show that at the beginning of true triaxial loading, the primary pores are gradually closed and the initial loading of the primary dense zone leads to a small amount of high and low wave velocity zones in the coal samples at this stage. With the increasing of the load, the primary pore compaction and the fracture of the dense zone result in the transfer and expansion of the high wave velocity zone and the formation of the abnormal wave velocity zone. When coal samples are close to failure, large areas of low wave velocity zones appear in coal samples due to the breakthrough of macroscopic fractures, and a large number of cracks in the interior make high wave velocity areas, wave velocity abnormal areas change and transfer rapidly, and coal samples are already in unstable state. At the stage of true triaxial high load holding pressure, due to the continuous compaction of coal sample fractures and the full destruction of internal structure characteristics, the sustained damage occurred in coal samples, represented by the decreasing of low wave velocity region and the increasing of whole wave velocity. In addition, in the true triaxial loading stage, the accumulative fracture release energy distribution in the coal sample is relatively concentrated, and its position corresponds roughly to the high wave velocity region and the wave velocity anomaly area, and the maximum value also increases continuously. When the coal sample is unstable and destroyed, the accumulative fracture release energy distribution is gradually dispersed and penetrated through the whole sample, but the maximum growth rate of the coal sample tends to be flat.
【學(xué)位授予單位】：中國(guó)礦業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TD313

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