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英文原文Analysis and application in controlling surrounding rock of support reinforced roadway in gob-side entry with fully mechanized miningAbstract: In order to optimize gob-side entry in fully-mechanized working face in moderate-thick-coal seams, we adopt a new attempt to pack roadside by pumping ordinary concrete, which is very important for the development of gob-side entry technology. The concrete has a long initial setting time and a low initial strength. So it is difficult to control the surrounding rock. In this paper, we analyze the effect of using roadside cable to reinforce supporting in gob-side entry surrounding rock controlling based on elastic-plastic and material mechanics knowledge. And then we propose a scheme that cable is used to reinforce roadside supporting and a single hydraulic prop is used as the temporary supporting in gob side. Using the numerical simulation software FLAC, we numerically simulated supporting scheme. Results of both the 2D modeling and the industrial test on No.3117 face in Jingang Mine prove that the scheme is feasible. The results show that the technology of protecting the roadway in gob-side entry retained efficiently make up the deficiency of roadside packing with ordinary concrete, effectively control the roof strata and acquire a good result of retaining roadway.Keywords: gob-side entry retained; surrounding rock controlling; cable reinforced roadside supporting; FLAC; single hydraulic prop; roadside support; pumping of concrete 1 IntroductionNowadays, gob-side entry retaining technology is widely used in many coal mines, particularly in mines where thin and moderate-thick coal seams are exploited. With the development of fully mechanized technology, the application of gob-side entry retaining can not only increase coal recovery rate, but also decrease roadway advance quantity, completely improved the tension situation of face replacement. Although the study of controlling surrounding rock in gob-side entry is practically valuable, there are some deficiencies in the course of studying and applyingfully-mechanized gob-side entry retaining:1) Roadside support system is laid more stress on, while the study of roadside reinforced support and temporary support in roadway maintenance is neglected when studying interaction roadway relationship of support surrounding rock.2) With the continuous increase of mining depth, it is more and more frequent that ground pressure comes into being in mining gateway, thus it is more difficult to control the surrounding rock. Metal props or timber support is used in gob-side entry while wood cribs, concrete blocks, high water quick setting and so on are used in roadside, which is a kind of single supporting way. Only when roof subsides on the support body, can its support resistance works. So the application of bolt and cable technology improves supporting ways.3) Roadway safety is the first important issue, however, good economic benefit in the course of roadway retaining also an issue to be considered. In the initial stage of roadside backfill supporting, the early stage compressive strength of concrete or high water quick setting wall cant meet the requirement, timber support, metal prop, and single prop are used as maintenance backfill in roadside close to the gob side. With the collapse and compaction of roof in gob area, these materials cant be recycled and the main tenance cost is increased.Take the problems above into account, in this paper we combine numerical simulation with theoretical analysis to prove the indispensable of cable reinforced support in roadside in gob-side entry retaining in full-mechanized working face, and provide a scheme that a supplementary single hydraulic prop is reinforced. Besides that, gob-side entry retaining test was carried out and the single hydraulic props were retrieved safely in gob-side. The test result is consistent with that in numerical simulation. It provides theory support and practical experience for fullymechanized gob-side entry retaining.2 Mechanical analysis of roadside reinforced support2.1Mechanical analysis of actively reinforcing surrounding rock controllingLath model from Sun Henghu and Zhao Bing 4-side rectangle plate load band segmentation is built. The location where maximum bending moment of rectangle overlay laminates and shear is as the roof load model for studying roadside support resistance on gob-side entry retaining (Fig. 1). 2Part FJCKH-F in the shadow in Fig. la is the localion of uniform load of roadside support resistance baring roof. The roof strata collapse mainly from dead weight (or dead weight and level stress), which is called active collapse, and is a main form of immediate and heaviest impact on boundary support. In this paper, roadside support resistance of roof in active collapse stage is studied. In Fig. 1b take a unit lath in rectangle ABCD to study retaining support resistance. Let the uniform load of roof be q, divide it into AC and DE by segmentation method. In the initial stage of working face mining, the deformation of roof strata subsidence is small, and level stress moment can also be neglected, thus, roof strata dead weight load is the only factor to be taken into consideration in the solution of roadside support .Material mechanics balance method is used to solve each section in Fig. lc. Analysis began with the first layer in roof, from below to above. The first layer is:Simultaneous solution of roadside support resislance can be obtained as:where is deadweight collection degree;the strata ultimate moment; the strata bend-ing moment; the downward shear from point A by strata breaking; the downward shear from point B by strata breaking; T the support force of coal body at the lower side of roadway to roof; the support force from roadside cable; a the retaining roadway width; xo the distance from the center of coal loosening area to point A;and h the characteristic size of broken strata.In ultimate condition, ，substitute it into Eq.(3), the roadside support roof-cut resistance can be expressed as:The above equation shows, roadside support roof-cut resistance concerns not only the overlying strata, but also the support of coal body at lower side of roadside. So the application of cable reinforced roadside can reduce effectively roadside support resistance.The calculation of roof-cut resistance in the second layer or above is different from that in the first one. In addition to being provided artificial support, the roof-cut resistance in the second layer or above needs another support from collapsed strata. As shown in Fig. 2, the following is the calculation model of roadside support resistance on gob-side entry retaining(the second layer).where , is the breaking point in the layer; and are the shear from the collapsed strata sheared remained border after the and second layer of roof being cut. Substitute and ，the strata deadweight collection degree, into Eq.(6), we havewhere is the size of each stratum breaking characteristics; is each stratum breaking point. Let and .Eq.(8) is the formula to calculate the roadside support roof-cut resistance on fully-mechanized gob-side entry retaining when the roof collapses actively. The item on the right in the equation is the moment caused by remained boundary deadweight, the second item is the total moment produced by collapsed strata shearing remained border at roof cut line, the third one is the ultimate moment of the mt layer in roof strata, the fourth one is the total bending moment from 1 to m layer at point A, the fifth one is the total moment produced by working slope coal supporting roof strata, the sixth one is the total moment produced by roadside cables supporting layers in roof strata. From Eq.(8), surrounding load generated from the first 3 items on the right of the equation is borne together by both roadway and roadside support. The roadway support resistance consists of force from working slope coal and support force from roof bolt (cable), while the roadside support resistance consists of roadside support resistance and roadside cable support, both of which from either roadside (coal and roadside) actively reinforced support system.2.2Mechanism analysis of cable reinforced surrounding rock controllingThe relationship between mine surrounding rock and support is a par t of rock mechanics. As the goaf is coming into being, stress field in a 3D stress state originally is redistributed; support pressure in surrounding areas is formed accordingly. Deformation and crack may immediately appear as strata turn into bidirectional or unidirectional stress from the 3D stress; consequently, the immediate roof may expose, break and collapse. Mechanical calculation model of each stratum is different from the study objective of material mechanism. And the scale of stress reducing area around mine is quite large. So in such stress circumstance passively reinforced support is the expediem option, in other words, its a kind of actively support in stress-reducing area. Considering time and space limit in mine, although the effect of using bolt (or cable) to reinforce support is limited, it postpones roof subsiding time and gains longer time for the roadside backfill setting on gob-side entry retaining. So it plays an important role in roadway maintenance. According to the study abroad, theres early and later stage in roof movement on gob-side entry retaining face, hence the key to success of gob-side entry retaining is effectively controlling movement of roof overlying strata in early stage6-9. Its helpful for analyzing surrounding rock movement pattern to simplify roof movement in the early stage to rectangle overlay laminates.From Eq.(8), moment caused by remained boundary deadweight is a constant value to a certain roadway maintenance width. Thus, the last 5 items on the right of the equation is the key factor to control surrounding rock movement. They relate to each other, reinforce strata maintenance, and reduce roadside support roof-cut resistance indirectly. In this paper, roadway bolt (or cable) support, and roadside cable reinforced support to actively control surrounding rock movement are discussed.The value of the second item on the right of Eq.(8) is mainly affected by roof collapsed strata shearing boundary C. As shown in Fig. 1, suppose k layer strata immediately collapse after cutting, and lose the mechanical relationship with the remained boundary C, the only item has relationship with m to k layer is left, whose value is .The collapsed layers within the k-1 layer have no effect on boundary, which reduce roof-cut resistance. Roof strata are reinforced by installing cable at roof above roadside support close to the goaf. Thus, the moment is enlarged, which is produced by cable supporting roof strata.This item shows moment produced by cable supporting roof strata, as well as stress relationship between strata. This item and have a proportional relation and affect each other.Roadside cables can be installed after roadway excavation or face advance. They should be installed immediately after face mining, which can not only reduce roadside support resistance in early stage to gain a good roof-cut effect, but also retrieve the roadside support maintenance materials safely. Nowadays,the backfill material for roadside support contains high water quick setting, ordinary concrete, and fly-ash-gangue concrete, and so on. At the early stage of roadside backfilling, both sides of the back filling body need to be maintained with I-beams, single hydraulic prop, timber, and so on, which should be retrieved in order to lower the cost and improve economic profit.3 Gob-side entry retaining support and calculation modelFig. 3 is a supporting model of gob-side entry retwining in fully-mechanized face in Jingang Mine, in which bolts and cables were used to support in roadway, cables were installed to support in roadside, single hydraulic props were used as temporary support on both sides of backfilling body at the early stage. As shown in Fig. 3, three rows of single props beside the goaf were used to provide operating room with a distance c when workers retrieved props. The mechanical state of immediate roof thats a kind of loose roof is different from that of the main roof, caving or serious bed separation might happen if support is improper or delayed. It will subside faster and more serious than the main roof. If support is proper, the immediate and main roof can move synchronously instead of the serious bed separation. And the integrity and bearing capacity of surrounding rocks are improved.Supporting model of gob-side entry retaining in Fig. 3 was transformed into a numerical cable support and single props in roadside, model 2 is built as well. The gob-side entry retaining in model 2 is 2.8 m wide, 2.1 m high, and the concrete backfill is 1.0 m wide with other parameters, which are the same as in model 1. Both models are 100 m long in horizontal direction, 70 m high in vertical direction. There are 8550 planes and 4-node units in each model. As shown in Fig. 4, an observation line A-A is drawn in lower boundary of immediate roof in each model.According to key strata theory and gob-side entry retaining roof strata movement，roadside was filled with only ordinary concrete, because coal in front of the face and un-mined coal in roadside supported the main roof, whose movement was restricted and balanced itself as being a plate form at the lower end of the face. Whereas, the immediate roof at the lower end of the face is different from the main roof in the aspect of mechanical state. The immediate roof, which is a loose roof, laid its load on the support body totally. If proper support is adopted, synchronous motion may take place between immediate and main roofs, bed separation may be improved and subsiding amount and speed of immediate roof may be reduced. All of these provide longer time for the concrete initial setting. Although the initial setting time of ordinary concrete is long and initial strength is low, if a suitable deformation amount is set properly and concrete collapsed degree and support compression conform to roof movement, concrete can be hardly or only little stressed. Thus the initial setting and strength of concrete can meet the requirements.Concrete wall was used as the backfill. The mechanical experiments of concrete standard samples with different proportions were carried out in the lab. The concrete ratio 0.5:1 of water to ash was experimented. Mechanical parameter of stratum was tested with American MTS 815 rock mechanism test system .Coal samples were picked from the mine concession with different impact-resistance coal seams in Jin-gang Mine, and processed to standard samples with 50 mm in diameter, 100 mm in height by drilling cores. The experimental result is shown in Table 2.4 Results and analysis of numerical simulationAs shown in Fig. 5, the vertical displacement of roof observation line is obtained by numerical simulation of the two kinds of support models with FLAC software.Fig. 5 shoves that, if gob-side entry retained according to model 1, the roadway central roof subsiding amount is low, only about 260 mm, while roadway central roof subsiding amount increases by almost 4 times without the roadside cable reinforced and single prop support at early stage. The roof subsidence is serious and cant meet the requirement of gob-side entry retaining, the effect is obvious to support temporarily with single props on both sides of concrete packing.5 Experimental verification The gob-side entry retaining experiment was carrtied out in No.3117 full-mechanized face, Jingang Mine, with a strike length of 1066 m, an average dip length of 130 m, and a mining height of 2.1 m. The coal seam with a gentle and stable pitch (110) contwined 0.54 m dark gray mudstone-coal line and soft coal. The immediate roof is 2.45 m black and gray mudstone with uniform texture. The main roof is 5.82m light gray siltstone. The roof is weak strata and the floor consists of 3.45 m gray and black argillaceous siltstone and 3.65 m gray fine-sandstone. The roadside backfill is 1.0 m wide and 2.02.2 m high.According to the theory and numerical simulation, tests were carried out in roadway in No.3117 fully-mechanized working face, Jingang Mine, several schemes were proposed, and two of them shall be discussed there. The first one with 500 m in length pumping concrete was used as backfill in No.3117 face, cables and bolts were used to support roadway roofs, and cables were installed to reinforce roadside roofs. At early stage of pouring concrete finished, 3 rows of pointed props or roof controlling were set up with single hydraulic props matched with hinge roofs behind hydraulic support moving forward, following the face advance. The array space in each row is 0.8 m and column space is 0.6 m. Two gangways are formed. The sketch of roadside primary support is shown in Fig. 6. The work was relatively easy as props supporting behind hydraulic supports formed an operation space. Props in roadside were retrieved by workers with swapping winches.The second scheme with a 150 m experimental length is the same to the first one except for cable reinforced support beside goaf and single prop temporary support.The deformation of god-side entry retaining roadway was obtained by field observation as shown in Fig. 7. In scheme 1, there is an approximately moving amount toward the centre of 220 mm in central roof and floor in roadway, and 235 mm in 2 working slopes, no bed separation is seen, partial subtle cracks within 3 mm in width. The concrete backfill is stable and the support effect is good, while in scheme 2, the moving amount increases by 27.3% in central roof and floor, 27.7% in 2 working slopes. 10 cm-deep rib spellings and many 20 mm-wide X-shaped cracks appeared in concrete wall. The mine pressure in gob-side entry retaining is very high and the wall reaches the limit state.Fig. 8 is the field effect after the movement of surrounding rocks calming down. According to field measurement, the load moved front lateral backfill at early stage to medial backfill as the mining effect reducing. It shows that the medial load is lower than lateral load because of the result of roof strata movement. The application of anchor nets as main support in transportation roadway in No.3117 fully-mecha-nized working face, Jingang Mine, which controlled broken expend of roadway surrounding rocks at early stage efficiently, no roof collapsed accident happened during the stage of gob-side entry retaining. The effect of concrete backfilling in roadside is good. Compared with new excavated roadway, the economic profit is 2.316 million Yuan by backfilling with concrete. A year later, from the gob-side entry retaining, its proved success that concrete pumping backfills effect in 3117 fully-mechanized face.6 Conclusions1) Mechanical model of gob-side entry retaining in fully-mechanized face is built, from which the equalion of roadside roof-cut supporting resistance is deduced; the mechanism of roadside cable reinforced support is analy.2) The result of numerical simulation with FLAC software shows that its efficient to use cable reinforced support in roadside and single props as temporary support beside golf.3) Roadside concrete backfilling experiments in gob-side entry retaining are proved efficiently. And practice shows that its feasible to use roadway bolt (or cable) support combined with roadside cable reinforced support. It provides reference theory and experience for the application of gob-side entry retwining technology in fully-mechanized working face and maintenance material retrieval in r
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