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英文原文An experimental study of a yielding support for roadways constructed in deep broken soft rock under high stressLu Yinlong , Wang Lianguo, Zhang Bei State Key Laboratory of Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou 221008, ChinaAbstract:A rationally designed support for deep roadways excavated in broken soft rock under high stress was investigated. The deformation and failure characteristics and the mechanism ofyielding supportwas studied for anchor bolts and cables. The rail roadway of the 2-501 working face in the Liyazhuang Mine of the Huozhou coal area located in Shanxi province was used for field trials. The geological conditions used there were used during the design phase. The newhighly resistant, yieldingsupport system has a core of high strength, yielding bolts and anchor cables. The field tests show that this support system adapts well to the deformation and pressure in the deep broken soft rock. The support system effectively controls damage to the roadway and ensures the long term stability of the wall rock and safe production in the coal mine. This provides a remarkable economic and social benefit and has broad prospects for fur-ther application.Keywords:high stress,broken soft rock, roadways, Yielding support, Yielding anchor bolt1 IntroductionThe depth of coal mining increases year by year as the reduction and depletion of coal resources in shallower parts takes place. The complex geological conditions deep underground, high ground stresses and structural stresses for example, cause some rock around the roadways to break down and rapidly expand under the high stress. After failure the area of broken rock has increased and the dilatant deformation pressure after cracking becomes very strong. Roof falling is accompanied by rib spalling and bottom heave on occasion. The roadways often require repeated maintenance and renovation for these reasons. Moreover, safety cannot be guaranteed and the costs of support are high leading to a decrease in mine efficiency 13. The stress environment, and the deformation and failure characteristics, of such roadways allow them to be dened as high stress, deep broken soft rock roadways.The object during support of high stress deep soft rock roadways is to stabilize the cracked rock that has considerable residual strength and intrinsic stability 47. Inadequate maintenance allows the roadway deformation to increase until, ultimately, there is a failure of the roadway. Therefore, a rational way to support deep broken soft rock roadways under high stress must be found.Studies have shown that support strength is the key factor for controlling the severe deformation of the roadway wall rock 812. In principle, only when the support strength is greater than 0.3MPa can deformation be effectively controlled. Practice shows that, however, the range of stress that the support structure can withstand is rather narrow before and after failure. No matter what kind of support is used the maximum stress that the support structure can bear is of the same order of magnitude. For example, the anchor bolt supports can provide from 0.05 to 0.2 MPa support. A single light steel frame can provide from 0.05 to 0.1 MPa of support while a heavy steel frame can provide 0.2 MPa of support. There-fore, for these roadways it is difcult to control the severe deformation by relying on the support capacity of a single type of anchor bolt or other support.As a consequence of this it appears necessary for the roadway to have a self-support capacity. The interaction between the wall rock and the support is such that the deformation of the wall rock is inversely proportional to the deformation in the support. Effectively stabilizing the deep broken soft rock roadway under high stress requires the support design to include intrinsic support from the rock wall, itself. The two important support parameters that can be adapted to supporting the stress and deformation are the carrying capacity and the reducible capacity. Making use of the self-support capacity of the roadway requires that the support system have both enough strength and enough yielding capacity. The support system then has the function of allowing some deformation that would otherwise be beyond its control. At the same time this yielding must be controlled in a way so the support system slowly releases the pressure in a given region while continuing to provide a supporting force. The yielding must not be free of restraining force. Thus, by allowing a certain amount of deformation in the wall that releases a part of the energy the pressure on the support system is reduced and larger deformation of the surrounding rock is effectively controlled. This partial release of energy can be called the unloading effect.In this paper a theoretical analysis and eld tests of the feasibility and technical issues related to a new high resistance, yielding support system are described. The 2-501 working face rail roadway of the Liyazhuang Mine in the Huozhou area is the specic location of the tests. High strength, yielding bolts and anchor cables with ribs form the core of the yielding support system.Technical parameters for application and a basis for further investigations are provided.Fig. 1. Ordinaryanchor bolt, steel belt, wire mesh, and anchor cablesupport in the test roadway.2 An overview of the test roadway2.1. Local geological conditionsThe Huozhou Coal Group Limited Liability Company operates a large coal mine in Jinzhong. This is one of the three major coal bases in Shanxi province and it is a subsidiary of the Shanxi Coking Coal Group. The Huozhou mining area is located in the Huoxi coaleld over the Huoshan fault. A poor coal bed with plenty of faults, no carbon columns, and prominent structural stress seriously restricts the safe production of the mine. The Liyazhuang Mine is a large mine built in the Huozhou area through the cooperation of China and Romania. The design production capacity of the mine is 1.5 million tons per year. The complex geological conditions of the mine include a typical soft coal rock with weak wall rock,prominent joint fissures, an easily weathering swell, abundant faults, and high tectonic stress. Since the initial construction of this coal mine methods like spray-over-anchors, arching, shed, as well as other means of support have been used. None of these have achieved the desired support effect and the roadway conditions continue to deteriorate. After excavating the roadways roof falls,bottom heaving, and rib spalling have been very serious problems.The repair of the main roadways is now 100% and the most serious sections have required repair up to four times. The daily procedures of transport, ventilation, and even walking can not be guaranteed so the costs of production have increased significantly.Thus, it is urgent to find new technologies for support in these roadways.Considering these problems in the Liyazhuang Mine, the rail roadway of the 2-501 working face was chosen as a test roadway.The length of 2-501 is 805 m at an average depth of 530 m. Theroadway is used for transporting materials, ventilation, and walking. The main roof of the working face is a ne sandstone, its bedding is a medium developed one, and its average thickness is 4 m.The immediate roof is a mudstone and a sandy mudstone that has obvious bedding development and is weathered and friable. The average thickness of the roof is 2.8 m. Number 2 coal contains two to three partings and is a coal with a complex structure. The average coal thickness is 2.89 m and the immediate floor has an average thickness of 2.5 m. This floor is mudstone, weathered,and friable, and its bedding development is obvious. The main floor has an average thickness of 3.0 m and is a ne sandstone with an obvious bedding development. Measurements of the three dimensional stress in the Liyazhuang Mine show that the maximum principal stress is a horizontal stress in the northwest to southeast direction. The minimum principal stress is also a horizontal stress and the maximum principal stress is from 2.09 to 2.26 times the minimum principal stress. The intermediate principal stress is close to vertical. The vertical stress also increases with increasing depth and the average lateral pressure co-efficient is 1.89.The section of the 2-501 roadway is 3400mm3000mm and the original support type was an ordinary anchor bolt, steel belt,wire mesh, and anchor cable design. Roof bolts are steel bolts 20 mm in diameter and 2500 mm long. The wall bolts are also steel bolts of the same diameter but 2000 mm long. The bolt row and line spacing is 850 mm800 mm. Anchor cable supports are also used and the cable length changes with changes in the rock properties. A two by two rectangular layout was used for the cables and the row and line spacing was 1.4 m1.6 m. The surface protection structure of the roadway is composed of W shaped steel strips and wire mesh.2.2. Deformation and failure of the roadwayField investigation showed that the roof and walls of the original construction had significantly deformed (Fig. 1). The statistics showed that the number of broken bolts was about 160 in total for 50 m of roadway for an average of 3.2 bolts per meter. Also, 20 anchor cables had broken in total. After installing I-beam shed supports in the locations where bolts had broken most of these beams subsequently bent and the maximum subsidence of them was about 200 mm.Further research found that bolts (or anchor cables) broke following certain rules over time. The roof pressure increased very fast the first day when bolts (or anchor cables) were installed. They then broke during the next day.Most of the bolts (or anchor cables) had broken within 12 weeks after their initial installation. Subsequent breaking of bolts (or anchor cables) did happen but the number of occurrences gradually reduced and the interval between events became longer. Note that breaking still occurred after bolts (or anchor cables) was reinstalled.The results of the eld investigation were analyzed and the deformation and failure of the test roadway was found to have the following characteristics:(1) During the initial period after roadway excavation the pressure and deformation release are intense. This period lasted several days. If no yielding measures are allowed for the supporting structures during this period the load increases to the point that the support will reach its load limits in a very short period. The support then breaks. Therefore, the initial intense deformation of the broken soft rock under high stress must be released through yielding of the support to avoid early breaking of the support structure.(2) After an initial intense deformation of the roadways the rock deformation rate begins to decrease. Rock deformation and failure gradually develop deep into the wall rock. This period usually would last about 1 month and during this period the intensity of roadway support should be increased. The self-support capacity should be fully employed to reduce the stress release and deformation rate in the surrounding rock.This helps to decrease further development of rock deformation and failure and to ensure the long term stability of the surrounding rock.The analysis shows that the initial deformation of the broken soft rock roadways under high stress cannot be resisted. It is better to adapt to the deformation and stress of the rock and make full use of its self-support capacity. A highly resistant but yieldingsupport structure should be used in these roadways.3. Support of broken soft roadways under high stress3.1. Mechanical properties of high strength, yielding boltsThe high strength, yielding bolt is a new type of extensible bolt that has been specially developed for complex roadways that have large deformation and are difcult to support. These bolts have high tensile strength and can develop a large initial pressure but they have special yielding properties that reduce the hazardous deformation of the roadway. Fig. 2 shows the basic composition of a high strength, yielding bolt. A special yielding tube is installed on the high strength yielding bolt between the bolt and the tray. This is the core component of this design. When forces on the bolt are big enough, because severe deformation of the rock has occurred, the wall rock pressure is released through deformation of this yielding tube. The force of the bolt can, therefore, be adjusted to adapt it to the development of wall rock deformation. The stability of the wall rock is thereby effectively ensured.The mechanical properties of the yielding tube were analyzed by performing a mechanical test in the laboratory. Fig. 3 shows a typical stress strain curve for the yielding tube 13. Note that the deformation of the yielding tube can be divided into three stages, namely; the stage of elastic resistance, the stage of constant plastic resistance; and, the stage of steady plastic resistance after yielding. The yielding consists of elastic deformation during the stage of elastic resistance from O to A in Fig. 3. The relationship between the stress and strain in this region can be expressed by Hookes law. From A to B the yielding of the tube due to plastic deformation at a constant load (the yield stress) is observed while the section continuously deforms until it is completely crushed. During the stage of steady resistance from B to C the yielding tube has been crushed and is in a steady state. The continued deformation is very small but the load is large.Research showed that the common bolting support for road-ways undergoing large deformations generally experiences the sequence of initial anchoring, increasing resistance, constant resistance, and finally, reduced resistance until failure 1416. The mechanical characteristic curve showing this is provided as Fig. 4.The special performance of the yielding tube in a high strength,yielding bolt regulates and controls the force on the bolt rod by yielding. A different mechanical property is developed, compared to the common bolt. The five stages of this bolt are shown as Fig. 5. These are the stage of elastic deformation of the yielding tube, from O to A, the stage of plastic yielding of the yielding tube,A to B, the stage of elastic deformation of the yielding bolt rod, B to C,the stage of plastic yielding of the bolt rod, C to D, and the stage of damage softening of the bolt rod, D to E. These special mechanical properties of the high strength, yielding bolt allow it to adapt to the deformation and failure of the rock and allow the self support capacity of the wall rock to come into play. This ensures the stability of the wall rock.3.2. Support mechanism of high strength, yielding boltsThe broken soft rock under high stress can only be reasonably supported if the self-supporting capacity of the wall rock is devel-oped by slow yielding of the support system. Of course, the condition that enough support strength can be guaranteed must be met. Partial release of the deformation in the surrounding rock decreases the pressure on the support system and the large deformation of the wall rock will then be effectively controlled. A support system made from high strength and highly pre-stressed, yielding bolts and anchor cables with rib cores, has high support pressure but also yielding performance. The basic mechanism contains the two following aspects:The bolts are effectively prevented from breaking to ensure that the whole support system does not fail at any time during the desired support period. The bolts are arranged in the rock so that the yielding tube of the bolt begins to yield under the pressure of large wall deformations. Then the bolts expand over a small, constant working distance. The resistance of the bolts dissipates energy from the rock deformation. The pressure of the support system yields to the harmful distortion and the support systems then effectively protected. Control of wall rock deformation during interim and late periods is also necessary so that further deformation of the deep wall rock can be controlled and the long term stability of the wall ensured. After the initial intense deformation the shaft of the high strength, yielding bolt bears increasing load as further slow deformation of the wall occurs. The high resistance it provides allows the self-support capacity of the wall rock to come into full play. Further deformation into deeper wall rock is reduced and the constant creep of the rock can be controlled to a stable range. This ensures the long term stability of the wall.Fig. 2. A Q500 high strength yielding bolt.Fig. 3. A stress strain curve of the yielding tube.Fig. 4. Mechanical properties of ordinary anchor bolts. Fig. 5. Mechanical properties of high strength, yielding anchor bolts.4. Field tests4.1. A high resistance and yielding support designThe deformation and failure characteristics of broken soft rock roadways under high stress located in the Liyazhuang Mine were used to design a support system using high strength yielding bolts and anchor cables with a rib core. A W shaped steel strip and wire mesh were used as supplemental support. Fig. 6 shows the support structure. Both numerical simulations and an engineering analogy method were used to determine the parameters required for the high strength yielding support.The specifications of the bolts are for Q500 high strength yielding bolts 20 mm in diameter by 2200 mm long. They are installed with a pre-stress greater than or equal to 4 KN. A larger, high strength 150mm150mm8mm number Q345 bolt tray is used during tting of the high strength bolts. The row and line spacing of the bolts is 800 mm 800 mm. The middle bolts are perpendicular to the roof and the bolts near the walls should be tilted to a 15 angle with respect to the walls. Each bolt is installed with one type CK2340 and one type Z2388 resin capsule.The specifications of these bolt calls for a Q500 high strength, yielding bolt 20 mm in diameter by 2200 mm long. The number Q345 bolt tray is also used here. The row and line spacing is 900mm800mm and each anchor bolt is installed with one Z2388 resin capsule.Anchor cables with ribs were used, see Fig. 7.Compared to common anchor cables the anchoring force of these cables is increased up to 30%. And, these cables have greater elongation before breaking. The combination of the roof strata conditions and the existing dynamic pressure suggested the specification of the anchor cables be 15.24 diameter by 6300 mm long. The anchor cable pallet is a at pallet that matches the anchor cables. The size of this pallet is 250mm250mm20mm. The installed pre-stress on the anchor cable is from 80 to 100 KN and the row and line spacing is 1800mm600mm. Two anchor cables are used in each row and each anchor bolt is installed with two Z2388 resin capsules and one CK2340 resin capsule.The roof and coal wall surfaces are controlled using a W shaped steel strip and wire mesh. This support supplements the bolt supports. The thickness of the steel strips used on the roof is 2.75 mm, their width is 275 mm, and their length is 3400 mm.The corresponding size of the steel strips used on the walls is 2.75mm275mm3100mm. The wire mesh is a diamond-shaped metal mesh with a 40mm40mm grid spacing.Fig. 6. High strength, yielding support structure of the test roadway (mm).4.2 Effect of the yielding supportThe eld test in the broken soft rock roadway began during September of 2007 and lasted more than 2 months. After 1 year of observation the roadway deformation showed the experiment was successful. This can mainly be seen in these observations:Deformation of the yielding tube occurred on most bolts in the test roadway. But almost no bolts or anchor cables broke. The phenomena of roof falling, bottom heave, coal spalling, and so on, did not appear during this time. Thus, the safety of the roadway was greatly improved. The deformation of the wall rock tended to abate over time.Three observation sections were set within the test roadway and four measuring points used at each observation section.These points were located at the roof, the floor, and at the midpoint of the walls. The converging deformation of the wall rock was measured at these stations. Fig. 8 shows the changes in the deformation at observation station I overtime. This figure shows that deformation of the wall gradually stabilizes after 90 days. The deformation rate of the wall rock eventually decreases to an average of about 0.12 mm/d. The high strength, yielding support system fully exercises its own anchoring effects as well as mobilizes the self-support capacity of the wall rock. The deformation and failure of the broken soft rock in this roadway under high stress were effectively controlled. The long term stability of the wall rock and safe production of the coal mine are effectively ensured.Thehighly resistant but yieldingsupport system, consisting of a high strength yielding bolt and anchor cable with a rib as its core, effectively ensures the stability of the wall rock. This significantly reduces roadway maintenance and repair costs. Compared to the common bolt, steel belt, wire mesh, and anchor cable support system the yielding design can reduce support costs by 1453.8 Yuan per meter of road- way. The full length of the 2-501 working face is 805 m so 1,170,300 Yuan were saved by this design. The yielding design has achieved remarkable economic and social Benets.Fig. 7. A schematic diagram of the ribbed anchor cable. Fig. 8. Deformation over time at observation station I.5. Conclusions(1) The initial deformation and pressure of the deep, broken soft rock under high stress are very intense after excavation. This often leads to damage of the traditional bolt support system after a short time. After the initial release of intense deformation the deformation rate begins to decrease and deformation and failure gradually move into the deeper wall rock.(2) A high resistance, yielding support system should be adopted to adapt to a highly stressed soft broken rock. This will allow release of the initial severe deformation of the wall rock and control the later slow deformation with its high resistance. In this way the long term stability of the wall rock is ensured.(3) The 2-501 working face rail roadway was used for a demonstration of a high strength yielding bolt and anchor cable design. The cable has a rib as its core and a W shaped steel strip with wire mesh were used as a support supplement.The eld tests showed that the high resistance, yieldingsupport system can effectively control rock deformation and failure. The long term stability of the wall rock and safe production of the coal mine are thereby ensured. This has achieved remarkable economic and social benets and so has great prospects for broader applicationAcknowledgmentsThis study was supported by the National Natural Science Foundation of China (No. 50874103), the National Basic Research Program of China (No. 2010CB226805) and the Natural Science Foundation of Jiangsu Province (No. BK2008135), as well as by the Open Foundation of State Key Laboratory of Geomechanics and Deep Underground Engineering (No. SKLGDUEK0905).中文译文深部高应力破碎软岩巷道让压支护试验研究陆银龙，王连国，张蓓摘要：首先研究一个设计合理的深部高应力破碎软岩巷道支护，研究了锚杆和锚索的变形和破坏特征以及让压支护的机理。我们对山西省霍州李雅庄煤矿2-501工作面的轨道平巷进行实验，在设计阶段采用了该矿的地质情况。新型的高强让压支护系统以高强让压锚杆和锚索为核心。试验表明，该支护系统非常适用于深部破碎软岩的应力和变形，可以有效控制巷道破坏，保证长距离岩壁的稳定性和矿井安全生产，保障了可观的社会经济效益，有很广泛的应用前景。关键字：高应力，破碎软岩，巷道，支护，可缩性支护，让压锚杆1 引言随着浅部煤层的开采，煤层的开采深度逐渐增大，深部地层复杂的地质条件，如高底板压力和结构压力，在高应力状态下引发巷道岩帮的破坏和快速坍塌，然后碎岩的破坏面积增大，开裂后的膨胀变形应力也会非常大,通常冒顶伴随着煤壁片帮和地板鼓起发生，所以巷道经常因为这些原因需要定期的维护和改造。此外，安全不能得到保证和昂贵的支护成本导致煤炭采出率的降低。这种围压强度和变形破坏特征的巷道定义为高应力深部破碎软岩。在深部高应力软岩巷道的支持对象是稳定的具有相当大的残余力量和内在稳定性裂隙岩体4-7。维护不足导致巷道变形增多，最终导致巷道完全破坏。所以，必须找到一个可靠的高应力深部破碎软岩巷道的支护。研究得出，支护强度是控制巷道岩壁严重变形的关键因素。理论上来讲，只有当支护强度高出0.3Mpa时，变形才能得到有效控制。现场经验表明，在完全破坏前支护结构可以承受的应力范围是表较小的。任何一种针对最大主应力的支护，其支护结构所能承载的应力是同一数量级。例如，锚杆支护可以提供0.05-0.2Mpa的支护强度，一个单一的轻钢架可以提供0.05-0.1Mpa的支护强度，而重钢框架，可以提供0.2Mpa的支护强度。所以，对于这些巷道是很难通过单一类型的锚杆或其他支护形式来控制严重的变形的。所以，对于巷道有自承能力是非常必要的，围岩和支护的相互作用结果是围岩变形和支护变形成反比关系，有效稳定控制深部高应力破碎软岩巷道不仅需要很好的支护设计，也包括围岩的自稳能力。可以适应支护应力和形变的两个重要参数就是承载能力和还原能力，要充分利用巷道的自稳能力必须要支护系统同时具备足够的强度和卸载能力。支护系统就会可以对围岩进行柔性支护，允许围岩变形，与此同时，这种卸载必须可以得到控制，通过支护系统在提供支护力的时候在特定区域释放压力，卸载必须不能脱离限制强度，所以，通过允许一定的围岩变形可以释放支护系统的一部分应力和能量，从而有效控制围岩变形程度。这种部分释放能量的方法便叫做卸载效应。在本篇文章中，主要阐述了一个新“高阻让压支护”系统的理论分析和井田可行性试验和技术问题。测试地点具体位于霍州李雅庄煤矿2-501工作面的轨道平巷，新型的支护系统以强度高、不易卸载的螺栓和锚索为核心，应用和作进一步调查的基础上的技术参数是已知的。Fig. 1. 普通锚杆、钢带、铁丝网和锚索在试验巷道的支护状况2 试验巷道概述2.1地质情况霍州煤电集团有限责任公司在晋中经营的大型煤矿，作为山西焦煤集团的子公司，是山西省三大产煤基地之一。霍州矿区位于霍希煤田断层之上。有大断层，无煤柱，以及突出的结构性压力的贫矿床严重制约了矿井的安全生产。李雅庄煤矿是中国和罗马尼亚合作在霍州地区兴建一个大型矿井。矿井的设计产量为150万吨每年。矿井地质条件复杂，包括典型的软煤岩与围岩弱面，突出的节理裂隙，易风化膨胀，较多的断层，和高构造应力。该矿基建以后，锚喷支护，拱形钢架支护，架棚支护等其他支护手段都已经使用，但是这些都没有达到预期的支持效果，而且巷道状况继续恶化。开挖后的巷道顶板下降，底部起伏，肋骨剥落已经非常严重的问题，主要巷道的维护率达到100%，最严重的部分需要4倍的修理时间，甚至日常的运输，通风，行人等都不能得到保证，使生产成本显着增加。所以，找到新型的巷道支护技术是当务之急。考虑到李雅庄煤矿存在的这些问题，选取其2501工作面轨道平巷作为试验巷道,该巷道长805m,平均深度为530m,平巷的主要用于运输材料，通风，行人。工作面老顶的岩性为细砂岩，层理中等发育，均厚4m;直接顶岩性为泥岩和砂质泥岩，有明显的层理发育并伴随着风化和破碎特征。煤层顶板均厚2.8m,2号煤包含两到三层的夹矸，而且煤层具有很复杂的结构，平均煤厚2.89m,直接顶为泥岩，风化破碎严重，均厚2.5m,而且层理发育明显。老顶均厚3m，层理发育明显。李雅庄煤矿的三向应力测量表明，最大主应力是在西北至东南方向的水平应力，最小主应力也是一个水平应力，最大主应力是最小主应力的2.092.26倍，中间主应力接近于垂直应力，垂直应力随着深度增加而增大，与平均侧压力的系数为1.89。2501轨道平巷的部分尺寸为3000mm3400mm，其原始支护方式为普通锚网，锚索支护，顶板锚杆采用20mm直径，2500mm长的螺纹钢，两帮的锚杆20mm直径，2000mm长，锚杆间间距为800850mm。同时也会采用锚索支护，其索长随着岩性的变化而变化，锚索通常用呈两个矩形布置，其间距为1.41.6m。巷道的表面保护结构通常用W型钢带和铁丝网。2.2巷道变形和破坏现场检测，巷道顶板和两帮已经有明显变形，统计数据表明，50m的巷道中破坏的锚杆总数为160根，平均每米3.2根；同时，锚索也坏了20根。在锚杆破坏的部位安装工字钢棚支护，随后工字钢弯曲，该处的最大沉降为200mm。进一步的研究发现，锚杆或锚索的破坏随着时间有一定的规律，在锚杆或锚索安装好的第一天顶板压力上升很快，然后第二天就会破坏，大部分锚杆或锚索会在安装好的12周内破坏。所以锚杆或锚索时有发生，但之后发生的次数会逐渐变少，时间间隔逐渐加长，值得注意的是，重新安装后的锚杆仍然有可能发生破坏。通过对现场的分析，试验巷道的变形和破坏有如下特点：(1)在巷道开挖的初始阶段，应力和变形急剧表现出来，该阶段持续几天。如果在此期间支护系统不能可以屈服，那么随着负载的增大，支护系统将在很短的时间内达到极限点，随之破坏。所以，深部高应力破碎软岩初始变形的增大一定要通过支护系统的弯曲释放，从而避免支护结构的早期破坏。(2)经过大巷的初期强烈变形后，岩石变形速率开始降低，岩石的变形和破坏逐渐转向岩石深部。此阶段通常持续一个月的时间，在此期间巷道的支护密度应该加大，同时应该充分利用支护围岩系统的自承能力降低围岩应力和变形速率，这有助于降低围岩变形和破坏的进一步发展，并保证围岩的长期稳定性。研究表明，高应力下深部破碎软岩的初始变形是不可避免的。最好的办法就是适应岩石的应力和变形，充分利用自承能力，所以提出高强度让压的支护系统用于此类巷道。3.高应力下的破碎软岩支护3.1高强让压机械锚杆高强让压机械锚杆具有可扩展性，是专门开发应用于有较大变形难以支护的复杂巷道，这些锚杆有很高的抗拉强度，会导致很大的初始应力，但有很好的卸载能力可以减少巷道变形的危险。如图2所示为此类锚杆的组成，在杆体上，在托盘和锚杆之间装有专用的让压管，这是该设计的核心部分。当巷道严重变形引发加载在锚杆上的应力足够大时，围岩应力就可以通过下压管路的弯曲释放。因此，锚杆的支护力度可以通过调节来适应围岩变形的发展，这样围岩的稳定性可以得到有效地保证。在实验室里通过机械测试分析
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