| With the implementing of government planning coal mining enterprises and integration of coal resource industry, the production capacity of a single coal has greatly been improved. The mode that one working face is planned in one colliery is extended.The level of modernization of the coal mine is gradually improved. In order to satisfy the need of modern coal mine, the development trend of large-scale equipment in working face becomes more and more obvious. The growth of roadway span and section is inevitable in large-scale intensive coal mine. Specifically, the roadway span is extended from original 3.5m to about 6m and the height is increased from original 2.5m to 4m.The section of the starting cut is also increasing and the span of it is increased from 5.0m to 8.0~10.0m gradually.The annual production capacity of Wangjialing coal mine is designed as five million tons. The designed useful width of starting cut in a fully mechanized caving face18101 is up to 9.5m.Aiming at the potential problem in the process of using and maintenance, research methods like site investigation, mechanical modeling, theoretical calculations, computer simulation, site construction test and measurement all are adopted in this thesis. The principle and corresponding technical of active control by composite cable truss are elaborated. The main research contents are as follows: The characteristics of deformation and damage in ultra-large section starting cut are researched and mechanical model is established to analyze the elastic, plastic and ultimate stage in the process of top coal beam of starting cut bending and getting failure.The minimum thickness of coal beam keeping self-stabilization and the way reducing the thickness of coal beam are obtained. Some programs of cable truss layout are analyzed in detail. The active controlling principle, layout program and superiority of composite cable truss is put forward. Considering the attenuation of pre-tightening force,the law of top coal beam neutral axis moving down in ultra-large section roadway is also analyzed. The key parameters such as angle, length, lapping width and span of composite cable truss are calculated and optimized in detail. The detailed supporting program which is suitable in site is obtained and implemented. The innovation of supporting is realized. The main conclusions are as follows:(1) Through the investigation and analysis on the deformation and failure characteristics of ultra-large section starting cut surrounding rock, the following problems of controlling surrounding rock analyzed: ? The parameter of original supporting way is not reasonable. The roof subsidence is serious when ordinary bolt-mesh-anchor supporting is adopted in 5m wide belt roadway. However, the span of starting cut is nearly two times as much as which of roadway. The level of maximum tensile stress and roof subsidence rise evidently.? Single cable could not supply thehorizontal pre-tightening force and horizontal support force which is not conducive to the state three-dimensional compressive stress and strength improvement of top coal and rock. It is especially harmful for the formation of a stable structure in the horizontal direction on supporting principle.?All the single cable and anchor are perpendicular to roadway roof or sides in the original scheme which hinders the shear performance of cable and anchor.?Single cable contacts with the roof on point. The anchoring point is located just above the roadway and could failed with roof separation and caving.Synergetic supporting effect could not be realized.?In the original supporting design of starting cut, resin medicine-one of cable and anchor is super rapid solidification and only a resin medicine-one is used in the roadway side. Due to the short solidification time, the resin medicine-one could not be fully mixed which does not comply with the principle of anchoring agent working. And the anchoring effect is poor.?In the original supporting scheme, the support strength of the anchor installed in roadway sides is lower. It does not meet the principle that the roadway sides must be controlled to control the roof.(2) According to the actual characteristics of starting cut maintenance, rectangular section anchoring beam statically indeterminate structure model in the starting cut in a fully mechanized caving face is established. The state of elastic, plastic and ultimate in the beam under the action of bending moment are analyzed. The expression of bending moment value is obtained. The minimum height of the roof rock beam without the effect of cable and anchor is calculated combining with the actual parameters of the starting cut 18101.The ways reducing the height of rock beam are present, such as improving cable and anchor and the yield strength of section. The reasons why cable and anchor could improve the stability of the rock beam are as follows: The anchor makes top coal in anchoring area form the structure of composite beam to bear together. The anchor helps shallow roof rock to be multi-axial stress state, which increases the yield stress of anchoring beam section. The active control by composite cable truss is adopted to not only supply horizontal pre-tightening force to the roof in anchoring rock beam but reduce and offset stress generated in the rock beam. The anchoring point is loaded in deep stable area under three-directional pressure of the roadway side. To prevent the anchoring rock beam from sinking is equivalent to reduce the span of the beam.Therefore, the stabilization of the rock beam could be realized.(3) The direction and strategy of controlling the ultra-large section starting cut surrounding rock are put forward:The supporting system structure should be improved when the cable and anchor are applied to supporting the ultra-large section roadway.The cable truss system is used in particular to supply horizontal supporting force needed by the ultra-large section roadway. And the supporting capacity is performed much better. The length and pre-tightening force of the anchor are designed and ensuredreasonably. The strength and size of anchoring rock beam in roadway roof is improved.The self-bearing capacity of rock beam is increased. The principle that the roadway sides must be controlled to control the roof is insisted. The supporting on side and corner of roadway are strengthened to prevent shear failure.(4) According to the requirement of supporting on ultra-large section roadway,single cable truss is taken as cable supporting basic unit and the "two-one" cycle mode is adopted at a certain row spacing to mount cable truss and dislocation overlap method is applied to different section in the active control system by composite cable truss. The strength, bearing force, cohesive force, force transmission of the roadway roof rock are made full use of. So the horizontal force applied to cable truss has an effect on the roadway roof in the maximum range. The stability and supporting quality of ultra-large section roadway are also improved. Its superiority in the span of roadway controlled is large and the horizontal supporting force in roadway roof is reasonable and in uniform distribution. The effect of cable truss is in reasonable allocation. The anchoring and connection are convenient, which meets the requirements of fast construction on site.(5) The concept of cable pre-tightening force attenuation is put forward. It is pointed that the rate of pre-tightening force attenuation is a constant value in the same kind of rock mass. Considering the attenuation of pre-tightening force, neutral axis analysis model of control by composite cable truss at ultra-large section starting cut roof rock beam is established. Under the effect of three groups of cable truss, the law of top coal beam neutral axis moving down in ultra-large section roadway is also researched.The calculation formula of sinking amount is deduced. In order to make the cable truss play a role, the view that sinking amount of the neutral axis must be positive is proposed in further. The method calculating maximum span of cable truss is also deduced.Combined with the characteristics of field parameters, the maximum span of cable truss of the active control by composite cable truss in ultra-large section starting cut of Wangjialing coal mine is calculated as 2.4m.(6) Three-dimensional numerical simulation model of 9.5m wide ultra-large section starting cut in Wangjialing coal mine is established by the numerical simulation software FLAC3 D in rock and soil engineering. The effect on controlling starting cut of key control parameters in active control system by composite cable truss is researched.The following key supporting parameters are optimized and determined: the corner cable angle, intermediate cable angle, cable length, lap length of cable truss and the roof anchor density and so on. Combined with the engineering analogy method, the material,diameter, length, row spacing of anchor and cable material, anchoring methods and the auxiliary parameters of other technological scheme are obtained. The overall layout of active control system by composite cable truss which could effectively control the stability of starting cut surrounding rock is determined. And the security simulation and analysis of the final design scheme are carried out.(7) Through the analysis of the specific characteristics of the starting cut 18101 in Wangjialing coal mine, the advantages of the technology controlling ultra-large section roadway surrounding rock and the optimization of key parameters of active control system by composite cable truss, the conclusion that active control system by composite cable truss should be applied to supporting the starting cut 18101 is drawn. The combined support system of cable truss-single anchor(cable)-steel strip-steel wire mesh is adopted to maintain the roadway in this scheme. The high-strength pre-stressed cable truss with the using of single pre-tension cable and high-strength and well-performance pre-tension anchor, metal mesh are adopted timely to support and reinforce the roof of starting cut. The combined supporting of high-strength thread steel anchor, steel joist and steel wire mesh is adopted in permanent supporting side of the coal. The combined supporting of fiber-glass anchor and diamond mesh is adopted in the coal side of the working face. The surface of surrounding rock in roadway forms a complete whole, dominating the deformation of the roadway effectively. Other supporting measures should be taken to strengthen the surrounding rock in time in the area where abnormal changes of the geological conditions occur.The industrial experiments of active control system by composite cable truss and mine pressure observation are carried out in the starting cut 18101 of Wangjialing coal mine. A full set of practical technology including cable truss supporting, construction method, construction technology, safety measures and mine pressure monitoring is obtained. The results of the site mine pressure observation show that :?In the nearly two months of observation, the overall convergence rate of the starting cut is very small.The convergence between the two sidewalls is less than 50 mm.Roof subsidence is less than 90 mm.The result of controlling surrounding rock is well. ? The speed of initial convergence of the starting cut is greater than later. After about ten days, the convergence between the two sidewalls tends to be stable and the roof need more time which is about fifteen days. ? The monitoring results of roof separation show that degree of top loosing and separation is light. The roof is stable.?Test results of testing anchoring force and tightening torque show that the qualified rate is high. The quality of construction is good and the supporting system is reliable when the anchor and cable are adopted to support the starting cut 18101. |
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