外文翻譯-沿空掘巷老頂?shù)姆€(wěn)定性分析

英文原文Stability analysis for main roof of roadway driving along next goafBAI Jian-biao(School of Energy Science and Engineering, China University of Mining & Technology, Xuzhou, China)Abstract: Focusing on the stability of surrounding rock around the roadway driving along next goaf with a narrow coal pillar, a mechanics model of the triangle block structure of main roof above the roadway is established, and the sliding stability coefficient K1 and the rotation stability coefficient K2 are proposed to describe the stability of the triangle block structure quantitatively. The structure can keep a self stability before and after the roadway excavation, at the stage of mining-induced effect, the stability of the structure is lowered, and the structure may become instability with decreasing the coal strength, increasing the mining height of working face and the mining depth.Keywords: roadway driving along next goaf; triangle block structure; stability analysisWith face advancing, the main roof results in periodic breaking, and the rock blocks after breaking are along the face strike direction formed into a voussoir beam structure. The breaking form in the face end is an arctriangle block 1 as shown in Fig. 1.In general, the roadway driving along next goaf can not affect the stability of arc triangle block structure in the upper working face, and affected by advance abutment pressure of the face mining, the stability of arc triangle block structure and the moving state must take place in greater change2, 3, and the field practice also indicated that the deformation of roadway driving along next goaf is smaller at the stage of the excavating influence and at the stable stage after excavation, but after the mining induced effect of the working face, the surrounding rock activity of roadway is violent and itsdeformation is also greater4.Fig. 1 The triangle block structure of roadway driving along next goaf1 Mechanics model of triangle block structure of main roof 21. 1 Establishment of mechanics model of triangle block structureAccording to Fig. 1, the arc triangle block structure is simplified as follows:(1)The triangle block B, rock mass A on the solid coal side and the block body on the side of goaf C form an articulated structure, because the periodic weighting advance of a working face is basically equal, i. e. the breaking characteristics of main roof is basically similar, the arc triangle block is simplified into the isosceles triangle block, called triangle block for short, and its side length in the rib is equal to the periodic weighting advance of the working face, other two sides are equal.(2)The soft and weak strata above the main roof are considered as loading exerting on the main roof, and before suffering the mining induced effect of working face, the weak strata above the triangle block B and the upper hard strata result in delamination and the force transmission is also lost.(3)When driving the roadway along next goaf with a narrow coal pillar, at the stage of mining induced effect of working face and under the superposed action of the side abutment pressure and the advance abutment pressure, the coals below the rock block A and the immediate roof as well as the waste rock below the rock block C should lead to compressive subsidence, but the rock block B results in rotation subsidence and its stability and position state should be changed.According to above simplification, a mechanics model of triangle block structure of roadway driving along next goof is established as shown in Fig. 2. Fig. 2 Section of mechanics model of triangle block structure (I-I section)1. 2 Study on the parameters of the triangle block BThere are mainly three parameters of the triangle block structure, i. e. the breaking length L1 of main roof along the face advancing direction, the breaking span L2 along the side direction and the breaking position X0 of triangle block in the coal seam, as shown in Fig. 1 .And the basic dimension of the triangle block B should be determined by the periodic weighting advance and the breaking pattern of the main roof during the periodic weighting. (1)Determination of L1 .From Fig. 1, it can be seen that the breaking length L1, of triangle block along the face advancing direction is the periodic weighting advance of the main roof, its value can be obtained by theoretical calculation and field observation, and L1 can be calculated by 5 (1-1)Where, h is the thickness of main roof, m; Rt is the tensile strength of main roof, MPa; q is the loading suffered by unit area of main roof, MN/m2. (2)Determination of L2. According to the analysis method of the plate yielding line, L2 is related to the face length S and L1, and L2 can be calculated by6 (1-2)On the basis of the calculating analysis6 , if S/L16, the crossrange span L2 of triangle block conforms to the periodic weighting advance L1 basically, and L1 is usually about 1020 m for the longwall face and the face length S is generally about 120250 m, that is, S/L1 is approximately 6 12. Therefore, it can be considered that the crossrange breaking span of the main roof in longwall face is equal to the periodic weighting advance of the main roof approximately, i. e. L2=L1. (3)Breaking position X0 of main roof. The breaking position of the main roof is located in the elastic-plastic crossing of coal seam7, X0 can be calculated by4 (1-3)Where, m is the mining height of working face, m; A is the lateral pressure coefficient; is the inner friction angle of coal seam, (); K is the stress concentration coefficient; is the mean volume weight of overlying strata, MN/ m3; H is the buried depth of roadway, m; C0 is the cohesion of coal seam, MPa; is the support resistance of roadway buttock in upper working face, MPa.2 Bearing analysis of triangle block2. 1 Bearing analysis of triangle block before roadway excavationThe diagram of triangle block bearing analysis of main roof before roadway excavation is shown in Fig. 3. For the convenience of analysis, the bearing pressure of the triangle block B can be simplified as follows:(1)The active force of front and rear 2C blocks on the triangle block B is equal, RBC, TBC are the resultant forces of horizontal thrusting force and vertical shearing force of block C on the triangle block B respectively, and the application point is in the middle of JK acting on a/2 along the height direction. The resultant forces of horizontal thrusting force and vertical shearing force of the crossrange rock block A on the triangle block B are RAB and TAB, and the application point is in the middle of JJ acting on a/2.Fig. 3 Diagram of bearing analysis of triangle block before roadway excavation(2)The weak strata above the main roof are considered as loading acted on it. The sole weight resultant force of the weak strata is FR, the sole weight resultant force of triangle block is FZ, and both act all on the center of gravity of the triangle block.(3)The supporting capacity of waste rock in goaf to the triangle block B is Fc, and the crossrange coals below the triangle block exist in limited balancing state, the supporting capacity of coals to the triangle block B is FM and the resultant force of mining induced abutment pressure is Fc.(4)The caving rock in goaf is compressed by the triangle block B during mining activity from the bulk increase coefficient to the residual bulk increase coefficient of the waste rock.2. 2 Bearing analysis of triangle block after roadway excavationThe roadway driving along next goaf is located in the coal seam below the triangle block structure. The roadway excavation can mainly change the supporting condition of coals for the triangle block, and in consideration of the more unfavourable conditions, the coal seam with a narrow coal pillar is situated at the residual deformation stage, thus the calculation can be carried out according to the residual strength, and after roadway excavation only the supporting capacity of coal seam has taken place in change, still using the stability of the triangle block structure after roadway excavation through analysis as shown in Fig.3. And at the stage of mining-induced effect, the bearing pressure of the triangle block B at the stage of mining-induced effect has following characteristics:(1)A part of weak strata overlying the triangle block B above the coal pillar is in contact with hard strata and transmits the mining induced abutment pressure, the resultant force of the abutment pressure is Fc.(2)Through the further rotation subsidence of the triangle block B, the caving waste rock in goaf is compressed from the bulk increase coefficient to residual bulk increase coefficient of waste rock.(3)The coal seam below the triangle block (including the narrow coal pillar) is situated in a position of the residual strength.3 Stability analysis of the triangle block structureThere are mainly two instability patterns of the triangle block structure, i. e. the sliding instability and the rotation instability. The sliding instability means that the shearing force between the rock block A and the triangle block B is greater than the friction force caused by the horizontal thrusting force between both rock blocks, the triangle block B slides along the rock block A. The rotation instability means that the rotation angle of the triangle block B is too big, the compression stress caused by the horizontal thrusting force between the rock block A and the triangle block B is greater than the effective compression strength in the contacting place of both rock blocks, so that the block mass is extruded and broken and leads to the instability. In order to prevent the sliding instability of both the rock block A and the triangle block B, the following conditions should be met: (3-1) is usually 0. 3 8.TAB is greater with the rotation of the triangle block B, and its result should lead to the extrusion and instability of the contacting place of both rock block A and rock block B, that is the rotation instability. For the sake of preventing the rotation instability of triangle block structure, the following conditions should be met: (3-2)where, is the mean extrusion stress on the contact surface, MPa; is the coefficient taken by the special bearing condition of rock block in a position of the rotation angle, usually taking =0. 3; is the compression strength of rock block, MPa.In order to analyze the stability of the triangle block structure, the concept of the stability coefficient of the triangle block structure is introduced, and the proportion of the friction force between both rock block A and rock block B to shearing force RAB of the triangle block structure is defined as the sliding stability coefficient K1 .The proportion of the extrusion stress between both the rock block A and the rock block B to the effective compressive strength in the contacting place of A and B rock blocks is defined as the rotation stability coefficient K2, that is, (3-3) (3-4)According to the formulas (3-1) and (3-3), if TAB0, RAB0 and K11, the triangle block structure may not lead to the sliding instability, and the greater K1 is, the better the stability. K11 indicates that the triangle block structure leads to the sliding instability, but if RAB0, i. e. in the vertical direction, the triangle block is supported by coal seam and the caving waste rocks, and the sum of the supporting capacity of coal seam and waste rock is greater than the sum of the shearing force of the front and rear two rock blocks C on the triangle block and the weight of the overlying soft strata and the triangle block, thus, the triangle block can keep its equilibrium without need of the upward acting force (RAB) of the rock block A on it. The calculating result is RAB0, so K10, K21 indicates the triangle block structure is resulting in the rotation instability; K2=1 shows that the triangle block structure is in a critical state.The stability analysis of the triangle block structure can be divided into three stages: after roadway excavation, before roadway excavation and a stage of face mining induced effect. According to the mechanics equilibrium, the bearing analysis for all stages of the triangle block is carried out to solve the stability coefficients K1 and K2.Each force takes a torque for the rotation axis EF, the torque of resultant force is zero, i.e. MEF=0; The resultant force in the vertical direction is zero, i.e.Fy=0; The resultant force in the horizontal direction is zero, i.e.Fx=0. Owing to longer calculating procedure, the detail is here no longer given. The basic conditions of the calculation are as follows: The proportion of the thickness of immediate roof and the mining height is 2, the thickness of the main roof is 6 m, the volume weight and the uniaxial compressive strength are 0.025 MN/m3 and 60 MPa respectively, the thickness and the volume weight of overlying weak strata above the main roof are 3.0 m and 0.020 MN/m3, the volume weight of overlying strata is 0.025 MN/m3, the bulk increase coefficients of coal seam and immediate roof are 1.4 and 1.35, the coefficient of lateral pressure is 0.4, the length of triangle block along the strike direction is 15 m and 15 m along the dip direction. And the mechanical property of the coal seam is listed in Table 1, the calculating results of the stability coefficient of triangle block are shown in Table 2. Table 1 The mechanical of the coal seamstratauniaxial compressive strength/Mpacohesion/Mpainternal friction angle/()soft coal10225middle hard coal204323. 1 Stability of triangle block before roadway excavationFrom the Table 2, it can be seen K1 0 before the roadway excavation, that is, in the vertical direction, the sum of supporting capacities of caving waste rocks and the coal seam for the triangle block B is greater than the sum of the shearing force of front and rear two rock blocks C on the triangle block and the weight of overlying weak strata and the triangle block, the triangle block B can keep its equilibrium without need of the upward acting force RAB of the rock block A on it. RAB0, i. e. the triangle block may not result in the sliding instability.Concerned in a relation between K2 and the mining height, increase of K2 with increasing the mining height means that the stability is decreased, and K2 changes not with increasing the buried depth of roadway, it presents the structure effect of the triangle block. K2 changes not with change of the mechanical parameters of coal seam, it indicates that the triangle block structure dont depend on the support of the coal seam and can reach self-equilibrium. Additionally, smaller K2 before the roadway excavation shows that the horizontal thrusting force among the rock blocks A, C and the triangle block B is smaller, and the triangle block may not result in the rotation instability.Table 2 Calculating results of the triangle block stabilitymining depth/mmining height/mbefore roadway excavationafter roadway excavationduring mining induced effectK1K2K1K2K1K2soft coal30030.0301 0.0326 0.0860 70.0356 0.0389 0.2410 50030.0301 0.0326 0.1600 70.0356 0.0389 0.3860 100030.0301 0.0326 5.7820 0.4810 70.0356 0.0389 4.5320 0.8480 middle hard coal30030.0301 0.0326 0.0543 70.0356 0.0389 0.2070 50030.0301 0.0326 0.1120 70.0356 0.0389 0.3270 100030.0301 0.0326 0.2230 70.0356 0.0389 0.7010 3. 2 Stability of the triangle block after roadway excavationAfter the roadway excavation, K1 is still smaller than 0, i. e. the triangle block may not result in the sliding instability after the roadway excavation. Compared with K2 before the roadway excavation, K2 is increased to some extent, but much smaller than 1 .This indicates that the stability of the triangle block structure after the roadway excavation is reduced, but it has gone down a little, and the triangle block can still keep its stable state. The roadway excavation has a little influence on the stability of the triangle block structure.3. 3 Triangle block stability influenced by mining activity (1)During the mining induced effect, K1 0, its value is also greater, and then the triangle block structure may not result in the sliding instability, but the change of K2 is greater, reaching 0. 9 in mining depth of 1000m. This indicates that the triangle block structure is close to the occurrence of the rotation instability. (2)The stability of the triangle block structure relates to the mechanical property of its lower coal seam, and the stability of medium-hard coal seam is higher than that of the weak coal seam. If the residual strength of the coal pillar is smaller than 1 MPa, the triangle block structure may result in the sliding instability. (3)The stability of the triangle block will be decreased with increasing the mining depth, but if the mining depth is smaller than 700m, the stability of the triangle block will be decreased a little with increasing the mining depth, and if the mining depth is greater than 700m, the strength of coal seam is decreased with increasing the mining depth and the stability of the triangle block structure is lowered rapidly. (4) The stability of the triangle block structure is reduced with incr