深部高应力破碎软岩巷道让压支护试验研究外文文献翻译、中英文翻译

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 nea