葛亭煤礦1.5Mta新井設(shè)計(jì)含5張CAD圖-采礦工程.zip,煤礦,1.5,Mta,設(shè)計(jì),CAD,采礦工程 Investigations of water inrushes from aquifers under coal seams（Jincai Zhang） Abstract：In many coal mines, limestone-confined aquifers underlie coal seams. During coal extraction from these mines, water inrushes occur frequently with disastrous consequences. This paper introduces the hydrogeological conditions of the coal mines and the potential water inrush disasters from aquifers under coal seams. It then presents the water inrush mechanism. The main factorswhich control water inrushes include strata pressure, mining size, geologic structures and the water pressure in the underlying aquifer. Analysis shows that reduction of confinement due to mining is the major cause of the water-conducting failure in the floor strata. The depth of the failure zone is strongly dependent on the mining width. This paper also presents field observation results of the water-conducting failure in the floor strata, and applies the finite element method coupled with stress-dependent permeability to analyze hydraulic conductivity enhancement due to coal extraction. Finally, theoretical and empirical methods to predict water inrushes are given, and technical measures for improving mine design and safety for coal extraction over aquifers are presented. These measures include fault and fracture grouting and mining method modification such as changing long-wall to short-wall Mining. Keywords: Water inrush; Coal mining; Confined aquifer; Strata failure; Stress and displacement; Hydraulic conductivity; Permeability 1 Introduction China continues to rely on coal for about 75 percent of its energy. Therefore, coal production is of crucial importance for China’s economy and development. However, mining operations in China are threatened by various kinds of groundwater during coal extractions. The most serious of the three main types of possible water disasters affecting the safe operation of coal mines [1] is water inrushes from the Ordovician limestone under the permo-Carboniferous coal seams in Northern China. The Ordovician limestone is a confined karst aquifer containing an abundant supply of water and with a very high water pressure. Furthermore, the strata between coal seams and the aquifer are relatively thin, varying in thickness from 30 to 60 m. Due to these characteristics of the aquifer, plus mining-induced strata failure and inherent geological structures (such as water-conducting faults, fractures) high-pressure groundwater can break through seam floors and burst into mining workings. Therefore, water inrushes from the aquifer occur frequently, and coal mines often suffer from serious water disasters during coal extractions. Water inrush incidents have shown that the maximum water inflow in a coal mine has reached as much as 2053 m3/min [2], which submerged the mine in a very short time. According to incomplete official statistics, about 285 of 600 key coal mines in China are threatened by water inrushes during coal mining [2]. The total coal reserves threatened by bodies of water are estimated at 25 billion tons. For example, in Northern China, the yearly coal production from the Permo-Carboniferous coal-bearing formations is more than 200 million tons. However, the coal extraction has been threatened by frequent water inrushes from the Ordovician aquifer. In this region, the lower level seams which have more than half of the total coal reserves are much more difficult to mine due to this threat of water inrushes (Table 1). From 1950 to 1990, a total of 222 serious water inrush incidents took place in China causing collieries to be submerged by water intrusions from the confined karst aquifers. More recently, total water inrushes at nationalized key coal mines occur about 125 times annually resulting in an economic loss of 1.5 billion Yuan (about 180 million US dollars). In addition, local coal mines run by provinces, counties, and private business have a larger annual economic loss induced by water inrushes. The main coalfields threatened by the Ordovician aquifer are Jiaozhuo in Henan Province, Fengfeng,Handan and Xingtai in Hebei Province, Zibo and Feicheng in Shandong Province, and Hancheng and Chenghe in Shaanxi Province. If the problems of safe mining over the aquifer cannot be solved efficiently,some coal mines in the mentioned coalfields will be faced with gradual reduction of production or even abandonment of the mines. In general, there are two different ways of solving the problems of mining over confined aquifers. One is to drain the aquifer before mining operation, and the other is to mine without drainage. Geological investigation and mining practice have unveiled that there are many environmental problems induced by water drainage from limestone aquifers, such as the Ordovician limestone aquifer in Northern China and the Maokuo limestone aquifer in Southern China. Fissures in these karstified limestones are well developed and interconnected within the aquifer such that when water is drained from one particular region, it has an extensive influence on the whole aquifer. For example, dewatering in the Ordovician limestone aquifer was conducted in Wangfen colliery, Hebei Province. The pumping flowrate was 96m3/min; however, the drawdown in the central well was only 2.8 m, and the radius of the cone of depression extended to 10km which caused the loss of many drinking water wells. This resulted in a shortage of water supply for 100 000 people. Therefore, water drainage is infeasible. The only solution for coal extraction over the limestone aquifers is to mine with technical measures and without drainage.In order to do so, it is of vital importance to study strata failure characteristics and hydraulic conductivity changes due to mining and thereafter find a way to predict and prevent water inrushes. Various researches has been conducted in this area [2–15]; however, the mechanism of water inrushes is still not well understood. 2 Determination of the water-conducting failure zone in the seam floor 2.1 In situ borehole observation of the water-conducting failure Coal extraction causes strata deformation and failure which may enhance hydraulic conductivity in the surrounding strata. Therefore, it is desirable to accurately determine pre- and post-mining hydraulic conductivities in the overburden and underlying strata of the coal seam. To measure the conductivity in the underlying strata, boreholes are drilled pre-mining in underground roadways for observation. In each borehole, water injection and a number of well logging techniques (such as electric resistivity, ultrasonic wave, acoustic emission, hole televiewer, etc.) are used to determine rock strength, borehole fissure, and changes in hydraulic conductivity. Fig. 1 gives a schematic diagram of a water injection instrument [16]. The key technique during measurements is to control the injection pressure. The pressure should not be high enough to create new fractures in the strata, since the experiment is conducted to determine the changes in hydraulic conductivity induced by mining. Therefore, the injection pressure should not exceed the least principal stress of the surrounding strata. Fig. 2 shows the observed borehole locations of and layout in Xingtai coal mine. In this area, in situ stresses were as follows: . The roadway in Fig. 2 was located 36m below the mining face and four boreholes were drilled at different angles. The water injection instrument described in Fig. 1 was applied to measure the flowrate of water injection preand post-mining, using an injection pressure of 0.35–0.5MPa. The water injection along each borehole was conducted by pumping water into the instrument, and then into the borehole. The measurements were taken in each hole at different sections throughout the borehole and at different times. Fig. 1. The instrumentation for water injection observation in a borehole Fig. 2. Observing borehole layout for water injection measurements in Xingtai coal mine, Hebei Province. Fig. 3. Flowrate of water injection along a borehole (Hole 1 in Fig. 2) pre- and post-mining in Xingtai coal mine, Hebei Province. Fig. 3 gives the measured pre-mining and post-mining flowrate of water injection in Hole 1 (refer to Fig. 2). Note that in this context pre-mining corresponds to a state before the mining face passes the borehole, and post-mining means after the mining face passes the borehole. It can be seen that before the mining face passed Hole 1 (in pre-mining, the mining face was 32m away from the borehole), the injection rate was zero from 53 to 68m in the inclined borehole. This means that the strata in this area were impermeable. However, when the mining face passed the borehole, the injection rate (refer to Fig. 3 for post-mining at 19 and 63 m) increased dramatically, and the strata in some areas changed from being impermeable to permeable. Since the borehole wall collapsed by mining when the mining face passed 63m from the borehole, water injection data could not be obtained after 60m from the borehole opening. The borehole collapse post-mining illustrates that the borehole was seriously damaged, and that rocks around the borehole failed due to mining. Fig. 4 plots the increments of water injection rates after mining, which were obtained by subtracting the pre-mining injection rates from those of the post-mining.These increments represent injection rates caused by permeability changes induced by coal extraction.It can be seen from Fig. 4 that along the inclined borehole from 43 to 72m (the borehole end), the injection rate increased compared to the pre-mining (in situ) state. Therefore, the strata in this area were fissured by mining, and this area is defined as the water-conducting failure zone. Using the same method to analyze the observed data from all boreholes, the mining-induced water-conducting failure zone can be obtained. This failure zone is of critical importance for mine design and water inrush prevention for mining over aquifers. Fig. 4 Flowrate increment of water injection along a borehole (Hole 1 in Fig. 2) after mining in Xingtai coal mine, Hebei Province. Fig. 5 displays the changes of the injection rates with the distance of mining advance for two different depths beneath the coal seam in Wangfen coal mine, Hebei Province. It clearly shows that in the mined area the injection rate increases significantly compared to the unmined area. It also can be seen that due to coal extraction, the water-conducting capacity increases in the floor strata, and this water-conducting capacity decreases as the distance from the coal seam to the floor strata increases. This means that the closer the strata are to the extracted seam, the higher the permeability in the seam floor. It is also noticeable that the injection rate decreases inside the abutment. This decrease is due to the fact that stress concentration and high abutment pressure occur in this area causing the fractures to be closed. Fig. 5 Flowrate of water injection versus mining distance for two different depths beneath coal seam (the negative distance represents pre-mining state and the positive means post-mining state). Fig. 6 Observing borehole layout and observation section of the water-conducting failure zone in the underlying strata for slightly inclined coal seam in Fengfeng coal mines, Hebei Province. Fig. 7 Observing borehole layout and observation section of the water-conducting failure zone in the underlying strata for inclined coal seam in Huainan coal mines, Anhui Province. Along both strike and dip directions, failure zones increase from upstream to downstream. Field observations have shown that characteristics of failures in the floor strata are considerably different for different inclinations of the extracted seams. For flat or slightly inclined seams (inclination angle, α<25°), the profile of the water-conducting failure zone is broad in section with extended lobes, and the maximum failure depth occurs beneath the headgate and tailgate, respectively, shown in Fig. 6. For inclined seams (25°<α<60°), the failure zone propagates downwards in an asymmetric manner in the dip direction, as shown in Fig. 7. The extent of the failure zone increases gradually from updip to downdip, and the maximum failure depth appears in the floor strata beneath the area around the lower gate. For steeply inclined seams (60°<α<90°), the failure zones in the floor strata are opposite to the inclined seams, i.e., the maximum failure depth appears in the strata beneath the area around the upper gate . 3Empirical prediction of the depth of the water-conducting failure zone According to in situ observations, a number of parameters affect the development and depth of the water-conducting failure zone. Mining width of the working face and uniaxial compressive strength of the strata are the most important of all parameters. An empirical formula for predicting the depth of the water-conducting failure zone was developed from field test results in long-wall and short-wall mining faces. The formula is expressed as (refer to Fig. 8)（1） where h1 is the depth of the water-conducting failure zone starting from the immediate floor of the seam (m) and Lx is the mining width of the mining face (m). Note that the observed data were obtained from coal mines in Northern China, with mining depths ranging from 103 to 560 m, and uniaxial compressive strengths from 20 to40MPa. For mining above aquifers, it is desirable to avoid water inrushes and the extra expense of strata dewatering. This can be achieved only when aquifers are located a certain distance outside the water-conducting failure zone. If an aquifer which is confined, very permeable and with abundant water lies within the failure zone, water with high pressure will rush into the mining area, and may cause a disastrous consequence. Fig. 8 Observed maximum depth of the water-conducting failure zone in the seam floor strata for different mining widths in China. 4Conclusions In situ measurements and physical modeling have shown that stress increases and abutment pressure is induced in the seam floor just before the mining face is reached. This causes compressive deformation and a decrease in the water injection rate. After mining, stress decreases and stress relaxation and confinement reduction are induced, causing expansion deformation and a water injection rate increase in the floor. Essentially, as mining advances, development of stress in the floor strata includes three stages: stress increase pre-mining, stress decrease post-mining, and a gradual recovery to the original stress. Corresponding to the stress redistribution, displacement in the floor strata shows compression before mining, expansion after mining, and gradual recovery to the original state. During the floor expansion and the stress relaxation stage, the strata are more prone to creating tensile fractures. In the area of transition between floor compression and expansion located beneath the area around the coal wall of mining face, the strata are likely to create shear fractures. Therefore, the floor failure zone is the largest in the strata right beneath the area around the coal wall, where water inrush is most likely to take place. Statistical data have shown that most water inrushes from the underlying aquifers were related to faults.Therefore, it is of crucial importance to detect and map geological structures in detail before mining. Also, since the mechanism of water inrushes from faults has not been fully understood, further study, including in situ monitoring of faults, needs to be undertaken. Since more than 60% of water inrushes were ascribed in some way to faults and other geologic structures, necessary measures are needed to address faults and inherent fractures in the floor before mining operations begin. For large faults, water-proofing barriers need to be left. For small faults and fractures, grouting can seal them and reduce the possibility of water inrushes. For weak aquifers existing in the seam floor, grouting cannot only change the weak aquifer into an impermeable layer but also increase the strength of the floor strata, which can reduce mining-induced failures. References [1] Zhang J, Zhang Y, Liu T. Rock mass permeability and coal mine water inrush. Beijing: Geological Publication House; 1997 [in Chinese]. [2] Zibo Mining Bureau. Data analyses and application of coal seam water inrushes in Zibo coalfield. Zibo Coal Sci Tech 1979; [in Chinese]. [3]Huainan Mining Bureau, Xi’an Branch of China Coal Research Institute. Hydrogeological conditions and control methods of the karst aquifer under # A coal seam in Huainan coalfield. Internal research report, 1983 [in Chinese]. [4]Fengfeng Mining Bureau, Shangdong University of Science and Technology. In situ measurement of the floor strata failure in the No. 2 coal mine of Fengfeng coalfield. Internal research report, 1985 [in Chinese]. [5] Wang, Z. Preliminary study of water inrushes from the floor of coal mining faces. Coal Geology and Exploration 1983; (5) [in Chinese]. [6] Wang, Y. Conditions and prevention of water inrushes from underlying confined aquifers of coal seams. Coal Sci Tech 1985;(1) [in Chinese]. 煤層下含水層突水機(jī)理研究 摘要：在許多煤礦，煤層下都存在石灰?guī)r承壓含水層。這些煤礦進(jìn)行煤炭開(kāi)采時(shí)，突水頻頻發(fā)生，造成災(zāi)難性的后果。本文介紹了煤礦的水文地質(zhì)條件和煤層下含水層潛在的突水災(zāi)害。然后給出了突水機(jī)理。導(dǎo)致突水的主要因素包括地層壓力，開(kāi)采規(guī)模，地質(zhì)結(jié)構(gòu)和下含水層水的壓力。分析表明，采礦使用限制減少是底板巖層水導(dǎo)電失敗的主要原因。失效區(qū)的深度主要決定于開(kāi)采寬度。本文還介紹了底板巖層中水承壓失效的現(xiàn)場(chǎng)觀測(cè)結(jié)果，并應(yīng)用有限元法和應(yīng)力滲透性的依從質(zhì)來(lái)分析由于煤炭開(kāi)采使?jié)B透系數(shù)提高的原因。最后，給出了預(yù)測(cè)突水的理論和實(shí)證方法，并提出了含水層上煤炭開(kāi)采礦井設(shè)計(jì)和安全的改進(jìn)技術(shù)措施。這些措施包括斷層和裂縫灌漿及采礦方法的改進(jìn)，如改長(zhǎng)壁開(kāi)采為短壁開(kāi)采。 關(guān)鍵詞：突水；煤炭開(kāi)采；承壓含水層；巖層破壞；應(yīng)力和位移；水力傳導(dǎo)系數(shù); 滲透率 1 引言 中國(guó)能源的約百分之七十五將繼續(xù)依賴(lài)煤炭。因此，煤炭生產(chǎn)對(duì)中國(guó)經(jīng)濟(jì)的發(fā)展至關(guān)重要。然而，在煤炭開(kāi)采過(guò)程中，中國(guó)采礦生產(chǎn)受到地下水的各種威脅。影響煤礦生產(chǎn)安全運(yùn)行的可能水災(zāi)害三種主要類(lèi)型中最嚴(yán)重的是中國(guó)北部石炭二疊系煤層下奧陶系石灰?guī)r突水。奧陶系石灰?guī)r有一個(gè)高水壓并有豐富的水源供給的密閉巖溶含水層。此外，煤層和含水層之間的地層相對(duì)較薄，厚度在30米至60米范圍內(nèi)變化。由于含水層的這些特點(diǎn)，再加上采礦誘發(fā)巖層破壞和固有的地質(zhì)構(gòu)造（例如水導(dǎo)電斷層，裂縫）高壓地下水可以通過(guò)縫地板和沖入開(kāi)采生產(chǎn)區(qū)。因此，含水層突水頻繁，煤礦常常在煤炭開(kāi)采過(guò)程中遭受?chē)?yán)重水害。突水事件表明，一個(gè)煤礦的最大涌水量高達(dá)2053m3/min時(shí)，能夠在很短的時(shí)間內(nèi)淹沒(méi)這一煤礦。 據(jù)不完全的官方統(tǒng)計(jì)，中國(guó)600個(gè)重點(diǎn)煤礦中約有285在煤炭開(kāi)采過(guò)程中受到突水的威脅。受到水體威脅的煤炭總儲(chǔ)量估計(jì)在25億噸。例如，在中國(guó)北部，從石炭二疊系含煤地層中每年生產(chǎn)煤炭超過(guò)200萬(wàn)噸。在這個(gè)區(qū)域，超過(guò)煤炭總儲(chǔ)量一半由于這種突水（表1）的威脅開(kāi)采要困難得多。 從1950年到1990年，在中國(guó)發(fā)生222個(gè)嚴(yán)重的突水事故，密閉巖溶含水層的突水導(dǎo)致煤礦被淹沒(méi)。最近，國(guó)有重點(diǎn)煤礦每年共發(fā)生突水約125次，造成經(jīng)濟(jì)損失15億元（約1.8億美元）。此外，省，縣，民營(yíng)企業(yè)經(jīng)營(yíng)的地方煤礦每年由于突水導(dǎo)致的經(jīng)濟(jì)損失更大。 受奧陶系含水層威脅的主要煤田是河南焦作，河北峰峰、邯鄲、邢臺(tái)，山東淄博、肥城，和陜西韓城、澄合。如果關(guān)于含水層的安全開(kāi)采問(wèn)題不能有效解決，在上述煤田的一些煤礦將面臨著產(chǎn)量減少，甚至關(guān)閉煤礦的問(wèn)題。一般來(lái)說(shuō)，解決煤礦開(kāi)采承壓含水層問(wèn)題有兩種不同的方法。其一是開(kāi)采前進(jìn)行含水層排水，另一種是不帶排水渠的開(kāi)采。地質(zhì)調(diào)查和礦業(yè)實(shí)踐已經(jīng)表明，有許多因石灰?guī)r含水層排水引起的環(huán)境問(wèn)題，如中國(guó)北部奧陶系灰?guī)r含水層排水，和在中國(guó)南部的茅口石灰?guī)r含水層排水。石灰?guī)r巖溶裂隙和含水層之間的這種相互聯(lián)系，使得當(dāng)從一個(gè)特定的區(qū)域排水時(shí)，它對(duì)整個(gè)含水層有廣泛的影響。例如，在河北省王墳煤礦對(duì)奧陶系灰?guī)r含水層進(jìn)行了排水。該泵流量為96 m3/min，但是，在中央井地下水位的降低只有2.8米，該漏斗降落半徑擴(kuò)展到10公里，造成了許多飲用水井的損失。這導(dǎo)致100000人供水短缺。因此，排水是不可行的。石灰?guī)r含水層之上的煤炭開(kāi)采的唯一的解決辦法是利用技術(shù)措施，不進(jìn)行排水進(jìn)行開(kāi)采。為了做到這一點(diǎn)，研究巖層破壞特性及由于采礦水力傳導(dǎo)的變化是至關(guān)重要的，然后找到一個(gè)方法來(lái)預(yù)測(cè)和防止突水。雖然已進(jìn)行過(guò)這方面的各種研究，但對(duì)突的機(jī)制仍然沒(méi)有得到很好的認(rèn)識(shí)。 表1 在中國(guó)的煤礦受奧陶系含水層威脅的煤炭?jī)?chǔ)量 2 煤層底板下水承壓失效區(qū)的測(cè)定 2.1 鉆孔原位觀測(cè)水承壓失效 煤炭開(kāi)采引起的地層變形和破壞可能提高周?chē)貙拥臐B透系數(shù)。因此，最好是準(zhǔn)確確定開(kāi)采前后在煤層上覆和下伏地層的滲透系數(shù)。為了測(cè)量下伏地層中的滲透系數(shù)，鉆孔都在井下巷道開(kāi)采前打鉆以便觀察。在每一個(gè)鉆孔，大量的注水和測(cè)井技術(shù)（如電阻率，超聲波，聲發(fā)射，孔成像等）用于確定巖石強(qiáng)度，鉆孔裂隙和水滲透系數(shù)的變化。圖1給出了一個(gè)注水儀器原理圖。在測(cè)量過(guò)程中的關(guān)鍵技術(shù)是控制注入壓力。進(jìn)行實(shí)驗(yàn)以確定開(kāi)采引起的滲透系數(shù)的變化，壓力不應(yīng)該高到足以制造新的地層裂縫。因此，注入壓力不應(yīng)超過(guò)周?chē)貙拥淖钚≈鲬?yīng)力。 圖1 鉆孔注水觀測(cè)儀器 圖2 河北省邢臺(tái)煤礦注水測(cè)量鉆孔布局 圖2顯示了邢臺(tái)煤礦鉆孔位置布局。在這一區(qū)域，應(yīng)力如下：。圖2中的巷道位于采煤工作面的下方36米，并且四個(gè)鉆孔分別鉆在了不同的角度。圖1描述的注水儀器利用0.35MPa到0.5MPa注射壓力來(lái)測(cè)量開(kāi)采前后水注入的流量。沿每個(gè)鉆孔注水由抽進(jìn)儀器的水來(lái)控制，然后流入鉆孔。該測(cè)量結(jié)果是由不同地區(qū)和不同時(shí)間的每個(gè)鉆孔內(nèi)得出的。 圖3給出了測(cè)量開(kāi)采前后注入孔1的水流量（參考圖2）。請(qǐng)注意，在這種情況下開(kāi)采前對(duì)應(yīng)一個(gè)采煤工作面通過(guò)鉆孔之前的狀態(tài)，開(kāi)采后則對(duì)應(yīng)采煤工作面通過(guò)鉆孔后的狀態(tài)。可以看出，通過(guò)開(kāi)采工作面通過(guò)孔1之前（開(kāi)采前，采煤工作面離鉆孔32米遠(yuǎn)），傾斜的鉆孔從53至68米的范圍內(nèi)注入率是零。這意味著，在這區(qū)域的地層防滲。然而，當(dāng)工作面通過(guò)鉆孔，注入率（采后在19至63米參考圖3）急劇增加，而且在某些地區(qū)被不透水地層向透水性轉(zhuǎn)變。由于采煤工作面通過(guò)鉆孔63米時(shí)井壁坍塌，注水?dāng)?shù)據(jù)無(wú)法從60米之后的鉆孔獲得。采后的井壁坍塌說(shuō)明，由于采礦鉆孔被嚴(yán)重破壞，而且鉆孔周?chē)膸r石也被損壞。 圖3 河北省邢臺(tái)煤礦開(kāi)采前后沿鉆孔（圖2中的孔1）的注水流量 圖4 河北省邢臺(tái)煤礦開(kāi)采后沿鉆孔（圖2中的孔1）增加的注水流量 圖4給出了開(kāi)采后注水率增量，這是由從采后注入率減去的采前注入率得到的。這些增量表明由煤炭開(kāi)采引起的滲透系數(shù)的變化導(dǎo)致注入率的改變。從圖4可以看出沿傾斜鉆孔由43至72米（鉆孔結(jié)束），與開(kāi)采前（原位）狀態(tài)相比注射率上升。因此，在這地區(qū)的地層是由開(kāi)采破壞的，而這個(gè)地區(qū)也被定義為水承壓失效區(qū)。使用相同的方法來(lái)分析所有鉆孔的觀測(cè)資料，可以得到由采礦引起的水承壓失效區(qū)。這個(gè)失效區(qū)域?qū)τ诘V井設(shè)計(jì)和預(yù)防含水層之上的礦井突水至關(guān)重要。 圖5顯示河北省王墳煤礦煤層下面兩種不同深度下，注入率隨開(kāi)采距離的變化。這清楚地表明，與未開(kāi)采的區(qū)域相比，在采空區(qū)注入速度明顯增加了。這也可以看出，由于煤炭開(kāi)采，底板巖層中的水的承壓能力增加，并且當(dāng)煤層與底板巖層之間的距離增大時(shí)水的承壓能力下降。這意味著，地層離裂縫越近，煤層底板中的滲透性越高。值得注意