Control over Surrounding Rocks Deformation of Soft Floor and Whole-Coal Gateways with Trapezoidal Su

un.200J. China Univ of Mining Tech (English Edition)Vol 15 No. 2Control over Surrounding rocksDeformation of soft floor andWhole- Coal Gateways withTrapezoidal SupportsZHAI Xin-xian', LI De-Quan, SHAO Qiang, SUN Yu-feng'Department of Resource and Material Engineering, Henan Polytechnic University, Jaozuo, Henan 454000, ChinacHangcun Colliery, Yima Coal Group Co Ltd, Sanmenxia, Henan 472300, chinaDepartment of Social Science, Shandong institute of Business and Technology, Yantai, Shangdong 264005, chinaAbstract: In Gengcun Colliery, Yima Coal Group Co. Ltd. the characteristics of the gateways of thick coal seam ande coal seam is with fully meed sublevel caving mining are that the thickness of roof coal seam of gateways islarger, their surrounding rocks are the whole-coal mass and the coal seam is prone to Spontaneous Combustion. withthe natural equilibrium arch theory, the reasonable adjacent distance of No Il mine-type metal supports was calculatedin trapezoidal gateways based on these characteristics. Then, in-situng experiments were carried out. Theresults indicate that under the action of virgin rock stress, the width of broken rocks zone of surrounding rocks is 17-20m in return heading and 1. 1-1.3 m in going headway. And their surrounding rocks belong to the IV-type soften rockand the lll-type aormmmn surrounding rock respectively. Therefore, under the movabledeformation is serious. It is suggested that the designed gateways hase pre-broadened cross section to suit theirdeformation At the same time, the accumulated water on gateway floor must be drained in time. These measures weretaken in the 1302 and 1304 coal faces in Gengcun Colliery, and the satisfactory results have been obtaineKey words: whole-coal gateway; gateway; the natural equilibrium arch theory; trapezoidal supportCLC number: TD 263.5 3: TD.21 Gateways of Fully Mechanized Coal spontaneous combustion one. The fully mechanizedFace with Sublevel Caving in Sponta. longwall mining with sublevel caving was used alongneous Combustion Coal Seamwith coal seam strike. In this section the coal seamstructure isis9°-12°The 1301 fully mechanized coal face with sub- The coal seam thickness ranges from 7. 4 m to 11.0 m,level caving is situated in the No I section of the its average value is 9.8 m. Its buried situation is morethird east mining district in Gencun Coal Mine of stable and its Protodyakonov scale of hardness f isYima Coal Group Co Ltd and the mined coal seam 1.0In中国煤化工 gths of coal face arewas the No2-3 thick coalThe coalhas 1000CNMHG The unit weight oflower methane content and belongs to No I typecoal seam is 1. 4t/m. The immediate roof and basicReceived 15 August 2004: accepted 20 November 2004Project 0511051900 supported by Natural Science Foundation of Henan ProvinceCorresppudhefeer.Tel:86-391-3980445:E-mailaddress:zhaixinxian@hpu.edu.cnZhAI Xin-xian et alControl over Surrounding Rocks Deformation ofoof of the 1301 coal face are black mudstone and a new balance and form a natural equilibrium archmedium-grain sandstone respectively, and their thick- The strata weight over the arch is borne by gatewaynesses are about 1. 42 m and 7.54 m respectively. Theribs and can not influence the coal mass within theimmediate floor is composed of carbonaceous mud- inner arch. Therefore, the vertical ground pressurestone,and the basic floor consists of mudstone and acting on the supports is equal to the weight of coald-mudstone. The return heading was excavated mass between the pressure arch and supports. It is outalong coal seam floor and driven with blasting of relation to rock mass or coal mass outside the archmethod. Its buried depth is about 181-217 m and has 2.1 Shape of natural equilibrium archtrapezoidal cross-section(the widths are 2.52 m and3.32 m and height is 2.47 m). The going headwaywas excavated by heading machine and its burieddepth is 204-233 m The headway also is trapezoidalcross-section(widths are 3. 42 m and 4.46 m, headay height is 3. 17 m). The cross-section of headway12.56m2Fig 1 Calculation diagram of the natural equilibrium arch2 Supporting Technologies of GatewaysThe parameters of the natural equilibrium archUsing Support and Shotcreting with mainly include its span and height Due to lowerWire meshcompressive strength of coal seam, some roof coal ofThe buried depth of gateways is shallow in the gateway begins to cave after gateway is excavated301 fully mechanized coal face with sublevel cavingMoreover, it is possible to cause the rib coal to slideThe stable coefficient of gateway surrounding rock toward gateway. The angle between sliding crack andM/Rc varies from 0.35 to 0.6. The surrounding rock vertical line is(90-9)/2. In the meanwhile, theis in the medium-stable state Based on the gateways pressure arch will be enlarged to produce a new pres-being whole-coal ones, the No 11 mine-used iron sure arch whose span is 2(a+c). Therefore,thesupports with wire meshes were used. In order to supports and gateway surrounding rock keep tempo-prevent gateways from causing fire, the shotcrete was rarily in a balance state(Fig. 1). The broken zonesprayed to enclose the gateways surrounding rock. So width of headway rib Cisthis supporting is called a support and shotcretingwith wire mesh-2C KyHBs cosa90°-tanBased on the characteristics of the whole-coal( Rcgateways of the 1301 fully mechanized coal face and2.3×0.025×218×1.110.5°coSof broken zone of gateways surrounding12rock being larger, the natural equilibrium arch theory3.17×tan90°-50.2was used to design the0.165m,(1)metal supports under the action of the moveable where: C is the broken zone width of headway rib, mabutment pressure. On the basis of this theory the top T is average unit weight of overlying strata, MN/moal completeness of whole-coal gateway is de- H is buried depth of headway, m; B, is the coefficientstroyed under the action of virgin fissures, joints and of residual pillar abutment pressure a is the inmining-Induced fissures with crisscross networ. e cline"凵中国煤化工 is the compressiveroof coal seam becomes a kind of loose material with strengCNMHG is headway height,smaller cohesion. When the gateway is affected by m; d is the internal friction angle of coal seam; k ismining action, its roof caving arises easily. While the the coefficient of stress concentration to consider theroof caves in to some degree, gateway roof can keep shape of headway cross-section, and the coefficient120J. China Univ of Mining Tech. (English Edition)VoL 15 No. 2of trapezoidal headway may be taken 2.3where: Mmax is the maximum bending moment ofThe height of the natural equilibrium arch of support top beam; w is the buckling croectionroof coal seam b ismodulus of support top beam, and the value of the10(a+c)osa_10(2268+0.165)cos10.5°No 1l mine-metal support is 1.445x10m q is loadK.Rintensity of support top beam; I is the length of sup3.987m,port top beam, 3.4where: b is the height of the natural equilibrium archWhile the curve deformation appears on supportof roof coal seam, m; K, is the stable coefficient of top beam under the action of roof pressure,theof coal seam, and it has relationship with its com- maximum tensile stress is in the middle of supportpressive strength, slicing thickness and the distance. top beam When tensile stress value varies from theamong the joint fissures etc. K, of the No 23 coalyield limit value of No II mine-metal a,(0 =343seam may be taken 0.5,R, is the compressive MPa)to its strength limit value o,(0,=510 MPa),strength of roof coal seam, MPa; a is the half span of the yield deformation of gateway support will hap-cantilever coal seam that sustains the curve deforma- pen 5, i.e., o, omax