本文選題：煤層群 + 采空區(qū)　； 參考：《中國礦業(yè)大學(xué)(北京)》2017年博士論文

【摘要】：煤炭是現(xiàn)今社會最重要的能源之一,長期以來,瓦斯作為一種災(zāi)害源,一直威脅著我國煤礦安全生產(chǎn),礦井瓦斯爆炸事故和煤與瓦斯突出事故時有發(fā)生,隨著開采深度的增加,這類問題更加嚴(yán)峻。根據(jù)大量理論與現(xiàn)場應(yīng)用實踐證明保護層開采及利用保護層開采的卸壓作用抽采被保護層卸壓瓦斯是最有效的區(qū)域性瓦斯治理措施和瓦斯抽采措施。因此,掌握保護層卸壓開采機理,卸壓范圍及其影響因素對精確布置瓦斯抽采鉆孔,提高瓦斯抽采濃度、消除瓦斯安全隱患均具有十分重要的意義。本文圍繞近距離煤層群上行開采層間裂隙演化規(guī)律及卸壓空間效應(yīng)展開研究,綜合運用理論分析、數(shù)值模擬、相似模擬實驗、工程實踐等手段對這一問題進(jìn)行了深入研究。在總結(jié)煤巖體中孔隙和裂隙的基礎(chǔ)上,運用彈塑性力學(xué)、斷裂力學(xué)等方法從細(xì)觀和宏觀角度分析了含裂隙煤巖體破壞特征和采動裂隙發(fā)育拓展機理,得到了覆巖離層裂隙和垂直裂隙發(fā)育機理;通過理論分析、相似模擬對長壁工作面采空區(qū)應(yīng)力恢復(fù)規(guī)律進(jìn)行了分析,指出了采空區(qū)應(yīng)力分布規(guī)律的復(fù)雜性及其主要影響因素,推導(dǎo)了采空區(qū)應(yīng)力恢復(fù)距離公式;基于采空區(qū)應(yīng)力分布規(guī)律,通過卸壓系數(shù)卸壓角得到了不同開采條件下煤層群開采覆巖的應(yīng)力場和位移場分布規(guī)律;通過UDEC數(shù)值模擬和相似模擬實驗得到了煤層群開采裂隙分布規(guī)律,得到了煤層群雙重卸壓開采與單一煤層開采不同的覆巖裂隙分布和演化規(guī)律。主要成果如下:1.采動煤巖體破壞特征及細(xì)觀裂隙演化機理(1)在成煤過程中及成煤后的地質(zhì)構(gòu)造運動使其內(nèi)部產(chǎn)生了大量的孔隙和裂隙,按照煤體內(nèi)孔隙直徑大小可將其分為微孔、小孔、中孔、大孔、可見孔及裂隙五個級別,按煤巖體中裂隙大小及形態(tài)可分為微裂隙、小裂隙、中裂隙和大裂隙四類。(2)根據(jù)摩爾-庫倫強度準(zhǔn)則分析了含單一貫穿裂隙圓柱體的強度及其破壞方式,當(dāng)β＜φw巖體的抗壓強度等于巖塊的抗壓強度,巖體只能沿巖塊發(fā)生剪切破壞;當(dāng)β＞φw,ko＜kw,且σco＞σcw時,裂隙巖體的破壞方式隨著圍壓的不同而不同,隨著圍壓的增大,裂隙巖體由沿裂隙面發(fā)生滑移破壞轉(zhuǎn)變?yōu)檠貛r塊發(fā)生剪切破壞;當(dāng)β＞φw,ko＞kw,且σco＞σcw時,裂隙巖體將始終沿裂隙面發(fā)生破壞,巖體的強度由裂隙面所決定;當(dāng)β＞φw,ko＞kw,但σco＜σcw時,若圍壓σ3＜σ3cr時,巖體裂隙面的抗壓強度大于巖石的抗壓強度,當(dāng)軸壓增大到一定程度時,裂隙巖體將發(fā)生剪切破壞,若圍壓σ3＞σ3cr時,巖體裂隙面的抗壓強度小于巖石的抗壓強度,當(dāng)軸壓增大到一定程度時,裂隙巖體將沿裂隙面發(fā)生滑移破壞,即在圍壓增加過程中,裂隙巖體破壞方式由巖塊剪切破壞到沿裂隙面發(fā)生滑移破壞;當(dāng)β＞φw,且ko＜kw,但σco＜σcw時,裂隙巖體將會發(fā)生剪切破壞,巖體的強度由巖塊強度所決定。(3)在增壓階段,煤巖體內(nèi)原生裂紋經(jīng)歷了剪切滑移-自相似擴展-彎折擴展-剪切擴展的發(fā)育過程;在卸壓階段,得到了軸壓卸荷過程中裂隙發(fā)生反向滑移的應(yīng)力條件及裂隙尖端的應(yīng)力強度因子,最大主應(yīng)力卸荷巖體卸荷過程中,軸壓卸荷到圍壓的過程中,裂隙反向滑移變形必然發(fā)生,而張開變形具有應(yīng)力條件;軸壓卸荷到零的過程,裂隙的張開和裂隙擴展都需要一定的應(yīng)力條件。2.近距離煤層群層間結(jié)構(gòu)及宏觀裂隙演化規(guī)律(1)基于關(guān)鍵層理論將近距離煤層保護層開采層間結(jié)構(gòu)類型分為:層間無關(guān)鍵層結(jié)構(gòu),層間含單一亞關(guān)鍵層,層間含兩個亞關(guān)鍵層,層間含多個亞關(guān)鍵層。(2)分析了頂板破斷形成豎向破斷裂隙應(yīng)滿足破斷變形強度條件及變形協(xié)調(diào)條件,得到豎向破斷裂隙的張開角度與巖層內(nèi)部下沉曲線方程的二階導(dǎo)數(shù)有關(guān)�；趲r梁的最大應(yīng)變理論推導(dǎo)出了將巖梁視為簡支梁時斷裂所滿足的跨度條件。(3)層間含多層亞關(guān)鍵層時,亞關(guān)鍵層的位置,層數(shù)會影響覆巖裂隙的動態(tài)發(fā)育和分布規(guī)律,亞關(guān)鍵層不會影響裂隙向高處發(fā)展,巖性和厚度相同的兩亞關(guān)鍵層對其層間裂隙范圍增大有抑制作用。3.煤層群上行開采機理及單一煤層開采圍巖裂隙演化規(guī)律(1)通過比值判別法、三帶判別法驗證了下部8#煤層作為保護層開采的可行性,通過彈塑性力學(xué)推導(dǎo)出了考慮采空區(qū)豎向尺度的采場頂板最大損傷高度,進(jìn)一步驗證了上行開采可行性。(2)研究了單一煤層開采圍巖裂隙演化規(guī)律,工作面煤壁前方應(yīng)力集中系數(shù)隨著工作面推進(jìn)先增大后趨于穩(wěn)定;在開挖之前,煤巖體垂直主應(yīng)力大于水平主應(yīng)力,當(dāng)煤體開挖后,主應(yīng)力大小和方向隨之變化;工作面煤壁附近頂板主應(yīng)力以水平應(yīng)力為主,垂直應(yīng)力幾乎為0,液壓支架對頂板的垂直應(yīng)力分布影響不大;底板的主應(yīng)力分布分為兩個區(qū)域,受支架底座影響,在底板1m范圍內(nèi),主應(yīng)力以垂直應(yīng)力為主,水平應(yīng)力較小,而隨著底板深度的增加,主應(yīng)力方向開始由以垂直應(yīng)力為主轉(zhuǎn)為以水平應(yīng)力為主,最后逐漸恢復(fù)為垂直應(yīng)力為主。工作面前方,主應(yīng)力變化趨勢近似“弧形”,從工作面前方煤體中部向頂?shù)装寤《仍絹碓酱?最大主應(yīng)力也由垂直主應(yīng)力漸漸變?yōu)樗街鲬?yīng)力;采空區(qū)后部垂直主應(yīng)力較采空區(qū)前部要大,逐漸趨于恢復(fù)原巖應(yīng)力狀態(tài);采空區(qū)圍巖應(yīng)力分布類似“拱形”,拱高隨工作面推進(jìn)先逐漸增大后稍有減小,最終穩(wěn)定在一定高度。(3)研究了采空區(qū)破碎巖體彈性模量對圍巖應(yīng)力場、位移場及裂隙場的影響規(guī)律,不同采空區(qū)應(yīng)力行為和不同工作面推進(jìn)距離展示出了相同的變形特征,頂?shù)装褰?jīng)歷了壓縮變形、卸壓膨脹變形、變形恢復(fù)、壓縮變形、無變形過程,但不同的采空區(qū)應(yīng)力行為條件下在大小和范圍方面有一定的不同,采空區(qū)跨落破碎巖體彈性模量越小,其采空區(qū)應(yīng)力恢復(fù)距離越大,工作面前方超前支承壓力集中系數(shù)、煤體破壞范圍、頂板垂直位移量及采空區(qū)頂板相同位置處圍巖膨脹—壓縮變形量均越大,越有利于煤巖體釋放彈性潛能,使瓦斯賦存狀態(tài)被激活越有利于覆巖瓦斯的解吸和流動,煤巖體透氣性增大,從而有利于瓦斯抽采鉆孔的布置和瓦斯抽采。4.采空區(qū)應(yīng)力分布規(guī)律及煤層群空間卸壓規(guī)律(1)研究了采空區(qū)應(yīng)力分布規(guī)律。運用采場上覆巖體載荷守恒計算模型、側(cè)向擴展支承載荷模型及基于地表下沉量的采空區(qū)應(yīng)力恢復(fù)距離擬合公式,以長平煤礦8#煤層84306工作面為例,當(dāng)采高為3m時,埋深為530m時,采空區(qū)應(yīng)力恢復(fù)距離分別為103,169,140m。采空區(qū)應(yīng)力恢復(fù)距離隨采高、垮落巖體破碎系數(shù)、煤層埋深呈正相關(guān),與采空區(qū)頂板巖體單軸抗壓強度呈負(fù)相關(guān),且與煤層埋深呈非線性關(guān)系;采高增大主要影響垮落破碎巖體碎脹系數(shù),其對采空區(qū)應(yīng)力恢復(fù)距離的影響較頂板巖性小。(2)得到了下煤層開采后覆巖空間應(yīng)力及其位移分布規(guī)律,根據(jù)下煤層保護層頂板垂直應(yīng)力和垂直位移分布情況,將頂板沿工作面推進(jìn)方向分為五個區(qū)域,自工作面煤壁前方到采空區(qū)依次為:原巖應(yīng)力區(qū)、壓縮區(qū)、膨脹區(qū)、應(yīng)力恢復(fù)區(qū)、重新壓實區(qū),分析了各區(qū)域內(nèi)瓦斯通道的形成和發(fā)育特點。(3)下煤層頂板不同位置不同高度的應(yīng)力分布均不同,距離下煤層越遠(yuǎn),垂直應(yīng)力較原巖應(yīng)力減小量越小,其三維應(yīng)力(SXX,SYY,SZZ)兩兩之間差值越來越小,較大的三維應(yīng)力梯度和應(yīng)力不對稱性會更容易造成煤巖體內(nèi)裂隙的產(chǎn)生、擴展及煤巖體破壞,距離保護層工作面越近,煤巖體產(chǎn)生的裂隙越多,且更容易發(fā)生破壞。(4)得到了下煤層推進(jìn)過程中,借助卸壓系數(shù)和卸壓角衡量的上煤層空間卸壓效果規(guī)律。隨著保護層工作面的推進(jìn),被保護層的卸壓程度和卸壓范圍逐漸增大,伴隨著直接頂和基本頂?shù)目迓?覆巖重力向煤壁方向和切眼轉(zhuǎn)移,使得產(chǎn)生應(yīng)力集中。隨著采空區(qū)頂板不斷下沉,采空區(qū)垮落破碎巖體的壓實,對頂板的支撐作用逐漸增大,從而使得在采空區(qū)中偏后區(qū)域的保護層卸壓程度有一定的減小,以采空區(qū)中軸線為中線,前后并不對稱,保護層最大卸壓處位于偏向工作面的方向。距離煤柱不同位置,沿煤層推進(jìn)方向卸壓角不同,切眼側(cè)和煤壁側(cè)卸壓角隨著靠近煤柱均先增大后減小;距離工作面煤壁不同位置,采空區(qū)沿煤層傾向卸壓角不同,煤柱側(cè)卸壓角隨著遠(yuǎn)離工作面先增大后減小。5.通過實驗室相似模擬實驗得到以下結(jié)論:(1)上煤層開采直接頂初次垮落步距和老頂初次斷裂步距均小于下煤層開采,下煤層推進(jìn)40m時,直接頂大面積垮落,工作面推進(jìn)到50m時,老頂斷裂,形成初次來壓,上煤層直接頂初次垮落和老頂初次來壓步距分別為30m和45m。(2)上煤層工作面推進(jìn)過程中,工作面?zhèn)瓤迓浣强傮w上呈現(xiàn)減小—增大—減小—增大的循環(huán)變化過程,頂板周期來壓步距為10m,20m,25m等,表現(xiàn)為工作面的大小周期來壓現(xiàn)象,伴隨著大周期來壓劇烈和小周期來壓不明顯,且基本表現(xiàn)為小周期來壓時垮落角減小,大周期來壓時垮落角增大的規(guī)律,這是由于覆巖關(guān)鍵層的破斷使得周期來壓步距和來壓強度都增大。(3)在下煤層開采過程中,上煤層的卸壓程度和卸壓范圍逐漸增大,工作面前方垂直應(yīng)力峰值點不斷前移,上煤層垂直應(yīng)力分布形式依次為“V”(基本頂未發(fā)生垮落)、“U”(基本頂初次垮落)和“W”(基本頂周期性垮落)型。(4)隨著下煤層工作面的推進(jìn),頂板周期性垮落和下沉,采空區(qū)側(cè)卸壓范圍和卸壓程度先增大后趨于穩(wěn)定,隨著采空區(qū)垮落破碎巖體逐漸被壓實,采空區(qū)底板逐漸恢復(fù)原巖應(yīng)力水平,通過對底板應(yīng)力監(jiān)測,底板經(jīng)歷了增壓—減壓—增壓—恢復(fù)的過程,采空區(qū)應(yīng)力恢復(fù)距離約為120m。(5)下煤層開采過程中,上煤層任一點都經(jīng)歷了壓縮,膨脹變形,膨脹變形增大,膨脹變形減小,膨脹變形穩(wěn)定這幾個階段,待采空區(qū)上覆巖層變形穩(wěn)定后,可將上煤層分為五個區(qū)域:壓縮變形區(qū),卸壓膨脹過渡區(qū),卸壓膨脹穩(wěn)定區(qū),卸壓膨脹過渡區(qū),壓縮變形區(qū)。上煤層裂隙也經(jīng)歷了發(fā)育-擴展-壓實閉合的動態(tài)過程。與數(shù)值模擬結(jié)果一致。(6)利用Matlab統(tǒng)計得到了下煤層開采過程中覆巖裂隙數(shù)量、長度和傾角的統(tǒng)計規(guī)律,裂隙總體數(shù)目隨工作面推進(jìn)呈“S”型曲線增長,得到了裂隙數(shù)目與推進(jìn)距離的擬合曲線,裂隙傾角以水平和垂直為主,覆巖中水平裂隙數(shù)量先增大后減小,獲得了隨工作面推進(jìn)不同距離覆巖整體裂隙傾角分布和切眼前方80-140m固定區(qū)域內(nèi)裂隙傾角分布玫瑰圖。(7)煤層群雙重卸壓開采展現(xiàn)出于單一煤層開采不同的覆巖裂隙分布和演化規(guī)律,覆巖裂隙經(jīng)歷了生成、擴展、壓實、張拉、再壓實的復(fù)雜動態(tài)過程,上煤層的開采使得覆巖裂隙二次發(fā)育,卸壓范圍和程度均增大,上下煤層開采形成的裂隙相互貫通,形成立體瓦斯運移通道。尤其開切眼和工作面煤壁側(cè)豎直破斷永久裂隙互相貫通,形成宏觀瓦斯通道。
[Abstract]:Coal is one of the most important energy sources in today's society. For a long time, gas is a source of disaster, which has been threatening the safe production of coal mines in our country, mine gas explosion accidents and coal and gas outburst accidents. With the increase of mining depth, this kind of problem is more severe. According to a large number of theories and field application practice, the protection layer has been proved. It is the most effective regional gas control measure and gas extraction measures to extract pressure from the protected layer by mining and using the pressure relief action of protective layer mining. Therefore, mastering the mechanism of pressure relief mining, the range of pressure relief and the influencing factors are all useful for the precise layout of gas extraction drilling, the concentration of high gas extraction and the elimination of the hidden danger of gas safety. It is of great significance. This paper studies the fracture evolution law and the pressure unloading space effect of the upper seam mining in the close range coal seam group, and makes a thorough study of this problem by means of theoretical analysis, numerical simulation, similar simulation experiment and engineering practice. On the basis of the pores and cracks in the total coal rock mass, the use of the bomb is used. Plastic mechanics, fracture mechanics and other methods are used to analyze the fracture characteristics of the rock mass and the development mechanism of the fracture development from the meso and macro angles, and get the development mechanism of the fracture and the vertical fissure of the overlying rock. Through the theoretical analysis, the similar simulation is used to analyze the stress recovery law of the goaf in the long wall working face, and the goaf should be pointed out. The formula of the stress recovery distance in the goaf is derived from the complexity of the force distribution law and the main influencing factors. Based on the distribution law of the stress distribution in the goaf, the distribution law of the stress and displacement fields of the overlying strata is obtained under the different mining conditions by the pressure unloading angle, and the coal is obtained through the UDEC numerical simulation and the similar simulation experiment. The distribution and the evolution law of the cladding fracture of the coal seam group are different from that of the single coal seam mining. The main achievements are as follows: 1. the failure characteristics of coal rock and rock mass and the evolution mechanism of the meso fracture (1) in the process of coal formation and the tectonic movement of the coal after the formation of coal, a large number of pores are produced inside it. According to the pore diameter of the coal, it can be divided into five levels of micropore, small hole, mesoporous, large hole, visible hole and fissure. According to the size and shape of the crack in the coal rock mass, it can be divided into four kinds: Micro fissure, small fissure, middle fissure and large fissure. (2) the strength and breaking of a single consistent fractured cylinder is analyzed according to the mole Kulun strength criterion. In bad way, when the compressive strength of the rock mass is equal to the compressive strength of the rock mass, the rock mass can only be shear failure along the rock block. When beta > W, Ko < kW, and sigma co > CW, the failure mode of the fractured rock mass varies with the confining pressure. With the increase of confining pressure, the fractured rock changes from slip failure along the crack surface to the rock mass along the rock mass. Shear failure; when beta > W, Ko > kW and sigma co > CW, the fractured rock mass will always be destroyed along the fissure surface, and the strength of rock mass is determined by the crack surface; when beta > W, Ko > kW, but when sigma < 3 < 3cr, the compressive strength of the rock fracture surface is greater than the compressive strength of rock and rock, and when the axial pressure increases to a certain extent, the fracture rock is increased to a certain degree. When the compressive strength of the rock mass is less than 3cr, the compressive strength of the fractured surface of the rock mass is less than the compressive strength of the rock. When the axial pressure increases to a certain extent, the fractured rock mass will slip along the crack surface, that is, during the increase of the confining pressure, the failure mode of the fractured rock mass is broken from the rock mass to the fracture surface. > > W, and Ko < kW, but when sigma CO < CW, the fracture rock will be shear failure, the strength of rock mass is determined by the strength of rock block. (3) in the stage of supercharging, the primary cracks in the coal and rock experienced the development process of shear slip self similar expansion bending expansion shear expansion, and the fracture occurred in the process of unloading in the pressure unloading stage. During the unloading process of the maximum principal stress unloading rock mass, the reverse slip deformation of the crack will inevitably occur during the process of unloading to the confining pressure in the unloading process of the maximum principal stress unloading rock mass, and the opening deformation has the stress condition, and the opening of the fracture and the crack expansion all need certain stress conditions.2.. The interlayer structure and macro fissure evolution law of close range coal seam group (1) based on the key layer theory, the interlayer structure types of close seam protection layer are divided into two layers: there is no key layer structure between layers, the interlayer contains a single key layer, and there are two sub key layers in the layer, and there are multiple sub key layers in the layer. (2) analysis of the roof breaking and forming the vertical break fracture should be analyzed. The opening angle of the vertical breaking fracture is related to the two order derivative of the equation of the inner subsidence curve of the rock stratum. The span conditions for the fracture are derived based on the maximum strain theory of the rock beam. (3) the subcritical layer of the subcritical layer between the layers and the subcritical layers. The position and the number of layers will affect the dynamic development and distribution of the cranny of the overlying rock. The subcritical layers will not affect the development of the fracture to the height. The two subcritical layers with the same lithology and thickness have the inhibition effect on the increase of the interlayer fissure range, and the evolution law of the.3. coal seam group and the single seam mining peri rock fracture evolution (1) through the ratio discrimination method, three The feasibility of mining the lower 8# coal seam as a protective layer is verified with the discriminant method, and the maximum damage height of the stope roof is derived by the elastoplastic mechanics, and the feasibility of the uplink mining is further verified. (2) the fracture evolution law of the surrounding rock in single coal seam mining and the stress concentration coefficient in front of the coal face are studied. As the working face increases first and then tends to be stable, the vertical main stress of the coal and rock mass is greater than the horizontal main stress before the excavation. When the coal is excavated, the size and direction of the main stress change, the main stress of the roof near the coal wall is the horizontal stress, the vertical stress is almost 0, and the hydraulic support has little influence on the vertical stress distribution of the roof. The main stress distribution of the floor is divided into two regions, which is affected by the support base. The main stress is vertical stress and the horizontal stress is small in the 1m range of the floor. With the increase of the depth of the floor, the direction of the main stress begins from the vertical stress mainly to the horizontal stress. Finally, the vertical stress is gradually restored to the vertical stress. The front of the working face is in front, The trend of the main stress change is approximately "arc", and the arc of the coal body is more and more from the middle of the working face to the top and bottom. The maximum principal stress is gradually changed from the vertical main stress to the horizontal main stress. The vertical main stress in the rear of the goaf is larger than the front of the goaf, and gradually tends to restore the stress state of the original rock; the stress distribution of the surrounding rock in the goaf is similar to the "arch" "The height of arch height decreases slightly with the advance of the working face, and then decreases slightly, and finally stable at a certain height. (3) the influence of the elastic modulus of the broken rock mass on the stress field, displacement field and fracture field of the surrounding rock is studied, and the same deformation characteristics are displayed in different goaf stresses and different working faces, and the top and bottom are experienced. Compression deformation, pressure relief expansion deformation, deformation recovery, compression deformation, and no deformation process, but there are certain differences in the size and range of different goaf stress and behavior conditions, the smaller the elastic modulus of the broken rock mass in the goaf, the greater the recovery distance of the stress in the goaf, the pressure concentration coefficient of the front supporting pressure and the coal body breaking in the front of the work. The larger the expansion of surrounding rock expansion and compression deformation at the same position of the roof at the top of the goaf, the more it is beneficial to the release of elastic potential of coal and rock mass, and the activation of gas is more conducive to the desorption and flow of the overlying rock gas, and the permeability of coal and rock mass is increased, which is beneficial to the layout of gas extraction drilling and gas extraction. The stress distribution law of.4. goaf and the law of pressure unloading in the space of coal seam group (1) studied the stress distribution in the goaf, using the load conservation calculation model of the overlying rock mass, the lateral extended support load model and the fitting formula of the recovery distance of the goaf based on the surface subsidence, taking the 84306 working face of the Changping Coal Mine as an example, when the height of the coal seam is high. For 3M, when the buried depth is 530m, the stress recovery distance of the goaf is respectively the height of the stress recovery distance in the 103169140m. goaf, the broken coefficient of the rock mass, the buried depth of the coal seam is positively correlated, and the uniaxial compressive strength of the roof rock mass in the goaf is negatively related, and it has a non linear relationship with the buried depth of the coal seam, and the height increase mainly affects the broken rock broken rock mass. The influence of expansion coefficient on the stress recovery distance of the goaf is smaller than that of the top slate. (2) the spatial stress and displacement distribution of the overlying rock after the mining of the lower coal seam is obtained. According to the vertical stress and vertical displacement distribution of the roof of the lower coal seam, the roof is divided into five regions along the surface of the working face, from the front of the coal face to the goaf. The region in turn is the original rock stress area, compression area, expansion area, stress recovery area, recompacting area, and analyzed the formation and development characteristics of the gas channel in each region. (3) the stress distribution of the different height of the roof of the lower coal seam is different, the farther the coal seam is, the smaller the vertical stress is smaller than the original rock stress, and its three-dimensional stress (SXX, SYY, SZZ) The difference between 22 is getting smaller and smaller, the larger three-dimensional stress gradient and stress asymmetry will lead to the formation of cracks in the coal and rock, the expansion and the destruction of coal and rock, the closer to the working face of the protective layer, the more cracks produced by the coal and rock mass, and more prone to damage. (4) in the process of the coal seam propulsion, the pressure unloading coefficient and unloading are used. With the advancing of the working face of the protective layer, the pressure relief degree and the pressure relief range of the protected layer gradually increase, with the collapse of the direct top and the basic top, the gravity of the overlying rock is transferred to the direction of the coal wall and the cut of the eye, so that the stress concentration is produced. With the continuous subsidence of the roof of the goaf, the collapse area is broken down. The compaction of crushed rock mass increases the supporting effect of the roof gradually, thus reducing the pressure relief degree of the protective layer in the rear area of the goaf, taking the axis of the goaf as the middle line, before and after and unsymmetrical, and the maximum pressure unloading place of the protective layer is located in the direction of the working face. On the other hand, the pressure angle of the cutting side and the side of the coal wall increases with the coal pillar first increasing, and then decreases with the coal wall in different positions. The pressure angle of the goaf along the coal seam is different, and the side pressure angle of the coal pillar decreases with the increase of the working face and then the.5. through laboratory similar simulation experiment. (1) the direct roof collapse of the upper coal seam mining is first broken. The step distance and the first break distance of the old roof are less than the lower coal seam mining. When the lower coal seam pushes into 40m, it directly tops the large area, and the working face is pushed to 50m, the old roof is broken and the initial pressure is formed. The first fall of the top coal seam and the initial pressure step of the old roof are respectively 30m and 45m. (2) coal seam advancing process, and the side fall angle of the working face side. On the whole, the cyclic variation process of decreasing - enlarging - decreasing - increasing, the pressure step distance of the roof period is 10m, 20m, 25m, etc., which is characterized by the periodic pressure phenomenon of the working face, which is not obvious with the large period pressure and the small period, and the fall angle decreases with the small cycle pressure, and the fall angle increases when the large period pressure is pressed. The large rule, this is due to the breakage of the key strata of the overlying rock, which makes the periodic pressure step and the pressure strength increase. (3) during the mining of the lower coal seam, the pressure relief degree and the pressure relief range of the upper coal seam gradually increase, the vertical stress peak point in front of the working face is moving forward continuously, and the vertical stress distribution in the upper coal seam is in turn "V" (the basic top has not occurred. "U"), "U" (primary roof fall) and "W" (basic top periodic collapse) type. (4) with the advancing of the coal seam working face, the cyclical collapse and subsidence of the roof, the lateral pressure relief range and pressure relief level of the goaf first increased and then tended to stabilize, with the collapse of the goaf crushed rock mass gradually compacted and the bottom floor of the goaf gradually restored the original rock stress. Level, through the stress monitoring of the floor, the floor has undergone the process of pressurization, decompression, pressurization and recovery, and the stress recovery distance of the goaf.

【學(xué)位授予單位】：中國礦業(yè)大學(xué)(北京)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TD712.6
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本文編號：1889387