Study on optimization of underlying coal bed exploited depth for tunnel

中文3890字英文原文STUDY ON GATEWAY BOLTING EXCAVATED ININCLINED COAL SEAM(Northeastern University ,Shenyang 110006)(Chengdu University of Technology.Chengdu 610059)Abstract ：A typical gateway is analyzed using fully-deformable discrete element method. The fractured zone around the gateway is measured in field. Based on the measurement results and theoretical analysis, a comprehensive support scheme adopting bolt and steel belt is proposed. Discrete element method is used to asses the bolting scheme, and displacement monitoring in field is also carried out. Having been put into practice, it is proved that the scheme is both successful and rational. According to theoretical analysis and monitoring in filed , some important keynotes that should be noticed in gateway bolting practice are presented as well.Keywords: inclined seam; gateway; strata behavior; bolting; discrete element methodIntroductionInclined coal seam is generally regarded as seam with a dip single 25~45,which occupies a considerable proportion in both production and reserves in China. Problems related to strata control are, however, seldom studied, and researches on in-seam gateway are even[]1less . The maintenance expense of gateway in inclined seam is generally 30% higher than that in nearly flat and gently inclined seam. The reason why there exists a such phenomenon is complicated itself, another possible reason is the lack of the inherent strata behavior law.At present, problems related to in-seam gateway maintenance are highly emphasized and many studies on strata behavior and support of gateway are carried[]2~4out . Such researches play a positive role in gateway maintenance.However most of the researches are carried out in flat or gently inclined seams. Due to their locating in remarkably anisotropic media and environment, gateways in inclined seams are often subjected tounfavorable loads and deform unevenly, strata move more intensively than that in gently inclined seam, and the broken region is also large, which makes gateway support even more difficult.In view of the above-mentioned facts, we use fully deformable discrete element method in simulating strata behavior of gateway in inclined seam, and the loosed zone around the gateway is also monitored in field. Based on the results, a bolting scheme is proposed. After putting into practice, the scheme is proved to be effective and rational.1. Deform and fail features of gateway without any support1.1 Geologic conditionsThe study object is the No.36 seam in Baoshan Coal Mine , the dip angle of the seam is 35°and thickness is 1.0m, the geologic conditions are rather simple. The average buried depth is 440m. The immediate roof is 2 meters thick of fine sandstone and shale, the overall strength is low. Above the immediate roof is comparatively hard main roof. The floor is fine sandstone. The gateway width is2.2m and the gateway is excavated in irregular shape in order to keep the roof intact. The sidewallcoal is however rather soft and loose, and easily fails. The surrounding rocks of the gateway are not stable , roof and sidewall are apt to fall or break, which is dangerous to both production and human safety. The working face often stopped due to difficult maintenance of the gateways.1.2 Simulation of gateway deformation and failure with discrete element methodThe joint statistical results show that the surrounding rocks of the gateway are cut by two orthogonal joints, one group is the bedding plane of the coal measures, another group is normal to the bedding plane, mainly developed in the immediate roof. Because of the low strength of immediate roof, there often exist long joints that cross through the immediate roof. Such long joints play adominant part in roof falling. According to the spatial distribution of joints, a discrete element model is built as shown in Fig.1.Thecomputing parameters required are mainly based on measurement in field and some back analysis. The load applied to the model are gravitational stress field. Thediscrete elements are fully deformable so that he deformation of block can be involved.After the gateway is excavated, under the action of initial stresses, the upper sidewall coal firstly breaks, then the surface of the lower sidewall coal begins to yield. The abutments of the roof at the two sidewall transfer to deep solid coal in consequence .The immediate roof at the surface of thegateway begins to bend, bedding separate, fail and fall(see fig 2),as a result, large area of the roof falls until up to the main roof Some broken blocks may collapse when a small disturbance occurs, In the practical face, it is very difficult to deal with the fallen rocks, sometimes a chain collapse of upper immediate roof may occur if special attention is not paid, which makes the fallen rock disposal adifficult and dangerous task.The results indicate that two sidewall coals fail differently the upper coal breaks more intensively than the lower sidewall coal.According to the above-mentioned analysis, it can be seen that in middle to lowly hard thin inclined seam, the stability of the two sidewall coals is very important to the overall stability of the gateway. If the sidewall fails, then the abutments of the roof will transfer to deep solid coal, as a result the free span of the roof increases, which aggravates the unstable condition of the wholegateway .Such failure of surrounding rocks is even serious when it is subjected to mining influence .It is, thus the key to keep the sidewall solid and intact in order to keep the overall stability of gateway in inclined seams.2.Measurement of loosed zone around gatewayBased on loosed zone theory of excavation, a loosed zone is generally formed around the excavation if which the stress is lower than the initial stress. Owing to irregular shape of gateway in inclined seam and anisotropic media, the loosed zone around gateway is certainly in irregular shape. We use an ultrasonic jointdetector(Type SC-II by Fushun institute of Coal Science and Technology) to measure the loosed zone of the gateway. The test results are shown in Fig.3. The gateway was supported by two roof bolts 1.6m long with very slightly prestressed. The measured loosed zone is upper sidewall coal more than 1.8m, lower sidewall coal 1.4-1.5m, and the roof is 0.95-1.1m.The gateway can be stable without mining influence. But as long as being subjected to mining activity, the gateway will collapse wit sidewall failing and roof falling. In extreme case, the maximum caving height can reach as high as 4.0m.As a result , the gateway in the seam is very difficult to be maintained and the maintenance cost is thus rather high. The test results are coincided with the numerical calculation. So it is, therefore, necessary to reinforce the gateway including the sidewall comprehensively.3.Inclined combined beam model for roofboltsIn inclined seam, roofbolts combine roof together when bolt length is shorter than the soft and loose roof. Of course, if the bolt can be bolted at a competent stratum, then the bolting mechanism will become hanging over. A typical inclined combined beam model is illustrated in Fif.4. The beam is composed by several (total numbers of layers are k) different kinds of strata, with length L and thickness δ. It is assumed that (1) each layer of the beam is homogeneous, continuous and isotropic; (2) the beam conforms to small deformation and (3) each layer deforms together, and no slip along bedding occurs.According tostrengthcriteria of thebeam, theminimumthickness δcan bederived andthen the totallength of a bolt can be easily determined as follows:12l l l δ=++ (1) Where , 1l is the length of bolted end ; 2l is the length of outer part.Bolt spacing a can be derived by the criteria that no slip occurs along bedding planes. Besides the above-mentioned conditions, the safety of the combined beam must be checked to prevent it from longitudinal instability.When all the conditions are satisfied, roof bolt parameters can ready be determined. As for sidewall bolts, their length and spacing can be derived by soil bracing theory in soil mechanics.It should be noticed when roof is composed of weak and loose strata, some bracing measures must be taken to protect the integrity of the fragile roof.4. Bolting of the gateway and its assessment4.1 Support assessment by discrete element methodWe consider two case in order to compare , firstcase: only the roof is bolted; second case: both roof and sidewall are bolted.Having been bolted in the first case, the roof has a obvious higher stiffness and strength, in the initial stage, only slight deflection occurs. However, with the sidewall coal failing and caving, the free span of the roof increases, the roof gradually enters unstable stage, subsiding and bedding separating as shown in Fig.5. Compared with the unsupported gateway, the gateway with roof bolted can keep stability for much longer time even it destabilizes finally.In the second case, the sidewall coal deformation and failure are strictly controlled by the sidewall bolts, the sidewalls are stable. Roof deflects only a small amount. Displacement can be hardly seen in the block diagram(Fig.6).The overall surrounding strata are in stable conditions. Even influenced by mining activity thegateway only fails locally, the roof is, however rather stable. It is, thus important to adopt a comprehensive bolt support pattern including the sidewalls.4.2 Bolting scheme and its implementationBased on the inclined combined beam theory, gateway loosed zone measurement and discrete element analysis, four bolts 1.6m long are installed in the roof. At the outer end of each bolt, a testing device ispatent of National Bureau of China) to ensure that at least 20kN pretension is exerted. Bolt installed([]5spacing is 0.75m, array pitch is 1.0m. Due to rather developed joints, steel bends are used together with roof bolt to ensure support effectiveness and prevent local roof caving. The steel plate is 0.01m thick,0.89m long and 0.1m wide.The coal sidewall is reinforced by timber bolt with spacing 1.0m, timer bolt for upper sidewall is 2.0m long and 1.0m for the lower sidewall. The timber bolt is installed with no less 7.5kN pretension.In the influence zone of front abutment pressure, strengthened supports are added. Metal frictional prop with timber cap is set as temporary reinforcement. The reinforcement distance is 25m ahead of the working face. The reinforced props are arranged in the center line of the gateway.More attentions should be paid to gateway excavation procedure. The roof bolts should be installed as soon as possible after the roof is exposed, then the sidewall bolt. The maximum delayed time should be less than 6 hours, which can make the roof deform exceedingly and integrity worsening. After each construction cycle, the bolts near the driving face should be refastened to assure their anchorage force.4.3 Measurement of gateway closureIn order to assess the effectiveness of the support scheme, the gateway closure is monitored during its driving and working face retreating.The closure of roof vs floor, sidewalls and roof subsiding velocity are shown in Fig.7.It can be seen that when the working face is far away from the monitoring area, the deformation of the surrounding rocks is very small, indicating that the gateway is not influenced by face dynamic pressure , the support system can easily bear the static load of gateway itself. With the working face advancing, the gateway begin to sense the dynamic action of the working face.When the distance between the face and monitoring area is around 20 meters, the deforming velocity of surrounding is increasing obviously and the strata is moving remarkably, such response of the gateway is the dynamic action of the working face. The testing results show that the reinforced distance should be more than 20 meters. However , from the overall status of the surrounding rock, the gateway is in stable conditions and can satisfy the demand of coal transportation, air intake and other engineering function.In spite of the fact that there are 2~3 groups of joints distinctively shown if the roof, the roof is, however stable under the combined action of roof bolts and steel bens. The upper sidewall coal fails and falls in some places, but the depth is limited within 0.6m.Based on the facts in field, in brief, the support scheme is rational and effective. Good economic and rechnical benefit were obtained.5.ConclusionThe failure pattern of gateway in inclined seam is remarkably anisotropic. The failure zone is not only related to the mechanical properties of strata, but also closely to the stability of sidewall coal body. The sidewall coal failure causes the abutment points to transfer into deep solid coal, increase the free span of the roof and therefore worsen the roof integrity. It is, thus a key task to keep the gateway sidewall sound in gateway maintenance.By gateway loosed zone testing, combined with the inclined combined beam model, bolt parameters can be readily determined. Discrete element method can be adopted to verify the rationality and make some amendment . As for the roof with multiple soft and loose layers, ensuring bolt pretension and installing roof bolts as early as possible are the keys to make the roof stable. Meanwhile, to keep roof integrity with steel bends (sometimes metal net is needed) is another important measure. It is proved that bolting can be use in gateway with fragile and weak roof as long as necessary measures are taken, considerable economic benefit can be obtained.References1.陶连金. 大倾角煤层开采矿山压力显现及其控制[学位论文]. 沈阳：东北大学. 1996。

第23卷 第7期岩石力学与工程学报 23(7)：1154～11572004年4月 Chinese Journal of Rock Mechanics and Engineering April ，20042002年6月28日收到初稿，2002年8月28日收到修改稿。

* 中国博士后科学基金(2002031045)资助项目。

作者 王贵君 简介：男，45岁，1983年毕业于阜新矿业学院，2001年获德国弗莱贝格工业大学工学博士学位，现任副教授、北京科技大学博士后，主要从事岩土流变力学、地下存储中的岩石力学问题和岩土力学数值分析方面的研究工作。

节理裂隙岩体中不同埋深无支护暗挖隧洞稳定性的离散元法数值分析*王贵君(北京科技大学土木与环境工程学院 北京 100083)摘要 针对一高速公路隧道工程，应用离散单元法对节理裂隙岩体中不同埋深无支护暗挖隧洞的稳定性及其机理进行了数值分析。

分析结果表明，当节理的赋存条件不利于隧洞稳定时，浅埋隧洞(如埋深只有5 m)的稳定性不如埋深较大隧洞(如埋深50 m)的稳定性好；反之，当节理的赋存条件有利于隧洞稳定时，则浅埋隧洞的稳定性比深埋隧洞的稳定性好。

分析结果还表明，“压力拱”效应在浅埋隧洞节理裂隙围岩稳定性中起着重要作用。

关键词 岩石力学，节理裂隙岩体，暗挖隧洞，埋深，稳定性分类号 TU 451 文献标识码 A 文章编号 1000-6915(2004)07-1154-04DEM ANALYSIS ON STABILITY OF UNSUPPORTED TUNNELS INJOINTED ROCK MASSES AT DIFFERENT DEPTHSWang Guijun(University of Science and Technology Beijing ， Beijing 100083 China )Abstract The stability of unsupported tunnels in jointed rock masses at different depths is analyzed using the distinct element method. The analysis of an autobahn tunnel shows that the unsupported shallow tunnels (for example ，at a 5 m depth) are not as stable as those at a larger depth (for example ，at 50 m) if the joints are steep and there exist more joint sets ，and vice versa. The pressure-arch effect on the stability of jointed rock mass surrounding a shallow tunnel proves to be important.Key words rock mechanics ，jointed rock mass ，mined tunnel ，depth ，stability1 引 言在隧道工程中，上覆岩(土)层对隧洞既是加载体又是承载体，其自身的重力往往是构成隧洞竖向荷载的主要来源。

沿空掘巷小煤柱合理留设及锚注支护优化研究一、研究背景煤炭是我国的主要能源之一，而煤矿开采是煤炭资源的重要获取途径。

在煤矿开采过程中，沿空掘巷是常用的采煤方法之一。

而沿空掘巷采煤方法中，小煤柱的合理留设及锚注支护优化问题一直备受关注。

小煤柱是指在煤层开采过程中留下的未开采的煤柱，其主要作用是保护巷道的稳定，防止采空区向巷道传递应力，从而确保矿井的安全和有效开发利用。

而对小煤柱的合理留设及锚注支护优化是保障矿井安全和提高煤矿开采效率的重要问题。

二、研究意义煤矿开采过程中，小煤柱的合理留设及锚注支护优化研究对于提高煤矿开采效率、确保矿井安全、减少煤矿事故具有重要意义。

通过合理留设小煤柱和优化锚注支护，可以有效减少煤矿开采过程中的煤层压力，降低煤矿开采的安全隐患，提高煤炭资源的开采利用率，促进我国煤炭产业的可持续发展。

三、研究内容1.小煤柱的合理留设研究针对不同煤层及巷道的情况，通过实地调研和理论分析，确定小煤柱的合理留设参数。

综合考虑煤层的地质条件、巷道的尺寸和矿井的安全要求，确定小煤柱的留设范围及数量，以确保巷道的稳定和煤矿的安全开采。

2.小煤柱的锚注支护优化研究针对小煤柱的锚注支护方案，通过实验室试验和数值模拟，研究优化锚注支护的材料、结构和施工工艺，以提高锚注支护的稳定性和效果，确保小煤柱的保护效果，促进煤矿的安全开采。

四、研究方法1.实地调研通过实地调研，了解不同煤层和巷道的地质条件、煤层厚度和倾向、巷道尺寸和形状、巷道岩层的性质等，为小煤柱的合理留设和锚注支护提供数据支撑。

2.理论分析通过理论分析，对小煤柱的合理留设和锚注支护进行优化设计，确定小煤柱的留设参数和锚注支护方案，建立小煤柱的数学模型，进行参数敏感性分析，为煤矿的安全开采提供理论支持。

五、研究预期成果1.提出一套完整的小煤柱合理留设及锚注支护优化设计方案，为煤矿的安全开采提供技术支持。

2.建立小煤柱的数学模型，揭示小煤柱的留设参数对巷道稳定性的影响，为煤矿的安全开采提供理论支持。

第4()卷笫4期2022年4月Vol.40,No.4 Apr.2022文章编号：]009-7767(2022)04-0140-05DOI:10.19922/j.1009-7767.2022.04.140大断面砂岩隧道超、欠挖控制技术研究谢规球(中交第四公路工程局有限公司，北京100022)摘要：在强、中风化砂岩地质中开挖隧道时，极易产生超、欠挖问题。

I人1此，以广州市南山1号隧道人断面砂岩川钻爆法开挖工程为例，探究了超、欠挖的潜在影响因素;依据“弱爆破，少扰动”设计原则，结合实际动态调整方案，针对软弱断而提出了微震光面爆破技术，并针对台阶法施工提出了“光面爆破+预裂爆破''的设汁方案，合理地控制了钻孔精度，优化了装药参数,将隧道超、欠挖控制在合理范围内。

关键词：砂岩隧道；隧道超、欠挖；控制爆破；影响因索；控制技术中图分类号：U455.4文献标志码：BResearch on Over-under-excavation Control Technology forLarge-section Sandstone TunnelXie Guiqiu(China Communications Construction Fourth Highway Engineering Co.»Ltd.»Beijing100022,China)Abstract:During excavating tunnels in strong(in(l moderately iceathered sandstone geology.over-under-exc(ii•(itioil is very e(isy to occur.Taking the engineering of lar^e-section sandstone drilling and blast in excar a t i on of Ao.1 Tunnel in Nunshan as(in example,the potential influencing factors of over-exc(n(ili(m and under-excavation are explored.A ccording to the design principle of^iveak blasting.little disturbance'',combined with the actual(Ivnamic adjustment plan,the micro-seismic smooth blasting technology is proposedJor the weak section.The design scheme of u smooth blasting+presplitting blasting"is proposed for the step method construction.The drilling accuracy is re(is o n(il)1)c o n t rolle(1,the charging parameters is optimized.A nd over-under-excavation of tunnels is controlled within(i reasonable rtinge.Keywords：sandstone tunnel；tunnel over-under-excaralion；controlled blasting；in/luencing factors；control technology随着我国交通网络体系的不断更新完善以及公路与隧道建造技术的迅速发展，深氏隧道和深埋越岭隧道|的修建越来越多，但各种工程难题也会相应产生。