Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using ...Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using the fracture mechanics theory. The relationships between the fracture length of the roof and the working resistance of the supports were discovered, and the correlations between the load on the overlying strata and the ratio of the crack's length to the thickness of the roof were obtained. Using a working face of Jindi Coal Mine, Xing county Shanxi province as an example, the relationships between the fracture length of the roof and the working resistance of the supports were analysed in detail. The results give a design basis in hydraulic top coal caving supports, which could provide useful references in the practical application. On-site experiment proves that the periodic weighting step interval of the caving face is 15–16 m, which is basically consistent with the theoretical analysis results, and indicates that the mechanized caving hydraulic support is capable of meeting the support requirements in the mining of a super-thick but shallowly buried coal seam.展开更多
冲击荷载作用下的岩体层裂是围岩屈曲失稳及岩爆的重要诱发因素。为研究围岩内部浅层节理对层裂行为的影响,采用相关键元胞力学模型(Correlated Lattice Bond CellCLBC)对此问题进行数值模拟研究。为了便于分析,以冲击荷载作用下不含节...冲击荷载作用下的岩体层裂是围岩屈曲失稳及岩爆的重要诱发因素。为研究围岩内部浅层节理对层裂行为的影响,采用相关键元胞力学模型(Correlated Lattice Bond CellCLBC)对此问题进行数值模拟研究。为了便于分析,以冲击荷载作用下不含节理的石梁层裂作为参考,将其层裂裂纹作为参考裂纹,层裂位置作为参考位置。相对于参考位置,分别在石梁中预设平行裂纹和斜裂纹组(相对于参考层裂裂纹),然后模拟相同荷载作用下的层裂行为。研究结果表明:浅层节理是否对岩体层裂产生影响取决于其相对参考层裂的位置和夹角。当平行节理位于参考层裂以内(远离自由面)时,平行节理对层裂没有影响;而当其处于参考层裂以外(近于自由面)时,应力波将其拉开、扩展,形成阶梯状层裂。对于斜节理组情形则更为复杂,但对于不同斜节理组其共同点都会在参考位置处产生层裂,并且表层岩石(层裂以外)都会被切割成块体沿斜节理方向弹出。当斜节理组位于参考位置以内时,斜节理发生扩展至自由面;当其位于参考位置以外时,只是在参考位置发生层裂;而当其跨越参考位置延伸至自由面时,在参考位置以内会产生平行于斜节理的衍生裂纹。该研究揭示了含浅层节理的岩体层裂规律,为分析围岩层裂行为提供了有意义参考,进而为进一步分析围岩屈曲失稳和岩爆提供必要的前提。展开更多
Single edge notched bend (SENB) specimens were prepared from steel weldments and crack tip opening displacement (CTOD) tests were carried out at different temperatures. Two specimen geometries, square (B×B) and r...Single edge notched bend (SENB) specimens were prepared from steel weldments and crack tip opening displacement (CTOD) tests were carried out at different temperatures. Two specimen geometries, square (B×B) and rectangular (B×2B) were used with a/W ratio ranging from 0.1 to 0.5 to investigate the effect of notch depth on plastic rotation factor and CTOD toughness. The CTOD values at initiation ( δ i) and maximum load ( δ m) for shallow cracked specimens were found to be significantly higher than those for the deep notched specimens. The plastic rotation factor was experimentally determined for shallow cracked specimens and found to be about 0.2.展开更多
Based on the field observation results of ground pressure in shallow seam, the movement characteristics of overlying strata in front and behind and the subsidence of the earth’s surface are studied. Also, the paper a...Based on the field observation results of ground pressure in shallow seam, the movement characteristics of overlying strata in front and behind and the subsidence of the earth’s surface are studied. Also, the paper analyzes the stability of overlying bedrock according to the theory of voussoir beam’s "S-R" stability and the hypothesis of step subsidence. It points out that slide instability is the fundamental form of overlying bedrock movement.展开更多
文摘Based on break characteristics of roofs in fully mechanized top-coal mining of thick shallow coal seams, a fracture mechanics model was built, and the criterion of crack propagation in the main roof was derived using the fracture mechanics theory. The relationships between the fracture length of the roof and the working resistance of the supports were discovered, and the correlations between the load on the overlying strata and the ratio of the crack's length to the thickness of the roof were obtained. Using a working face of Jindi Coal Mine, Xing county Shanxi province as an example, the relationships between the fracture length of the roof and the working resistance of the supports were analysed in detail. The results give a design basis in hydraulic top coal caving supports, which could provide useful references in the practical application. On-site experiment proves that the periodic weighting step interval of the caving face is 15–16 m, which is basically consistent with the theoretical analysis results, and indicates that the mechanized caving hydraulic support is capable of meeting the support requirements in the mining of a super-thick but shallowly buried coal seam.
文摘冲击荷载作用下的岩体层裂是围岩屈曲失稳及岩爆的重要诱发因素。为研究围岩内部浅层节理对层裂行为的影响,采用相关键元胞力学模型(Correlated Lattice Bond CellCLBC)对此问题进行数值模拟研究。为了便于分析,以冲击荷载作用下不含节理的石梁层裂作为参考,将其层裂裂纹作为参考裂纹,层裂位置作为参考位置。相对于参考位置,分别在石梁中预设平行裂纹和斜裂纹组(相对于参考层裂裂纹),然后模拟相同荷载作用下的层裂行为。研究结果表明:浅层节理是否对岩体层裂产生影响取决于其相对参考层裂的位置和夹角。当平行节理位于参考层裂以内(远离自由面)时,平行节理对层裂没有影响;而当其处于参考层裂以外(近于自由面)时,应力波将其拉开、扩展,形成阶梯状层裂。对于斜节理组情形则更为复杂,但对于不同斜节理组其共同点都会在参考位置处产生层裂,并且表层岩石(层裂以外)都会被切割成块体沿斜节理方向弹出。当斜节理组位于参考位置以内时,斜节理发生扩展至自由面;当其位于参考位置以外时,只是在参考位置发生层裂;而当其跨越参考位置延伸至自由面时,在参考位置以内会产生平行于斜节理的衍生裂纹。该研究揭示了含浅层节理的岩体层裂规律,为分析围岩层裂行为提供了有意义参考,进而为进一步分析围岩屈曲失稳和岩爆提供必要的前提。
文摘Single edge notched bend (SENB) specimens were prepared from steel weldments and crack tip opening displacement (CTOD) tests were carried out at different temperatures. Two specimen geometries, square (B×B) and rectangular (B×2B) were used with a/W ratio ranging from 0.1 to 0.5 to investigate the effect of notch depth on plastic rotation factor and CTOD toughness. The CTOD values at initiation ( δ i) and maximum load ( δ m) for shallow cracked specimens were found to be significantly higher than those for the deep notched specimens. The plastic rotation factor was experimentally determined for shallow cracked specimens and found to be about 0.2.
文摘Based on the field observation results of ground pressure in shallow seam, the movement characteristics of overlying strata in front and behind and the subsidence of the earth’s surface are studied. Also, the paper analyzes the stability of overlying bedrock according to the theory of voussoir beam’s "S-R" stability and the hypothesis of step subsidence. It points out that slide instability is the fundamental form of overlying bedrock movement.
