According to the distribution of abutment stress in a stope,this research established the mechanical model of mining abutment pressure transmission in floor base on the theory of semi-infnite plate body in elasticity....According to the distribution of abutment stress in a stope,this research established the mechanical model of mining abutment pressure transmission in floor base on the theory of semi-infnite plate body in elasticity.This study takes the 762 working face of Haizi Coal Mine as a case in point,and analyzed the dynamic evolution law of seam floor stress during the mining process.With an organic combination of the mining floor stress and surrounding rock stress,the study obtained the change laws of the maximum principle stress and the minimum one for the floor roadway surrounding rock when mining the upper working face.Considering the non-constant pressure force state and the cracks revolution mechanisms of floor roadway surrounding rock,the research built the mechanical model of roadway stress.Simulation results verify the reliability of the above conclusions.Moreover,this model could provide the theoretical basis and technical support for controlling floor roadway surrounding rock.展开更多
Abutment piles in soft ground may be subjected to both vertical and horizontal soil movements resulting from approach embankment loads. To constrain the soil movements, the soft soil ground beneath the approach embank...Abutment piles in soft ground may be subjected to both vertical and horizontal soil movements resulting from approach embankment loads. To constrain the soil movements, the soft soil ground beneath the approach embankment is often improved using composite pile foundations, which aim at mitigating the bump induced by high-speed trains passing through the bridge. So far, there is limited literature on exploring the influence of the degree of ground improvement on abutment piles installed in soft soil grounds. In this paper, a series of three-dimensional （3D） centrifuge model tests was performed on an approach embankment over a silty clay deposit improved by cement-fly ash-gravel （CFG） piles combined with geogrid. Emphasis is placed on the effects of ground replacement ratio （m） on the responses of the abutment piles induced by embankment loads. Meanwhile, a numerical study was conducted with varying ground replacement ratio of the pile-reinforced grounds. Results show that the performance of the abutment piles is significantly improved when reinforcing the ground with CFG piles beneath the approach embankment. Interestingly, there is a threshold value of the replacement ratio of around 4.9% above which the effect of CFG pile foundations is limited. This implies that it is essential to optimize the ground improvement for having a cost-effective design while minimizing the risk of the bump at the end of bridge.展开更多
An investigation was conducted on the overall burst-instability of isolated coal pillars by means of the possibility index diagnosis method（PIDM）. First, the abutment pressure calculation model of the gob in side di...An investigation was conducted on the overall burst-instability of isolated coal pillars by means of the possibility index diagnosis method（PIDM）. First, the abutment pressure calculation model of the gob in side direction was established to derive the abutment pressure distribution curve of the isolated coal pillar. Second, the overall burst-instability ratio of the isolated coal pillars was defined. Finally, the PIDM was utilized to judge the possibility of overall burst-instability and recoverability of isolated coal pillars.The results show that an overall burst-instability may occur due to a large gob width or a small pillar width. If the width of the isolated coal pillar is not large enough, the shallow coal seam will be damaged at first, and then the high abutment pressure will be transferred to the deep coal seam, which may cause an overall burst-instability accident. This approach can be adopted to design widths of gobs and isolated coal pillars and to evaluate whether an existing isolated coal pillar is recoverable in skip-mining mines.展开更多
目的观察瓷基台和钛基台用于种植体支持全瓷单冠修复的美观效果以及两者对种植体周围软硬组织的影响。方法 19例单颗上颌前牙缺失患者,分为瓷基台组(8例)和钛基台组(11例),行种植体支持全瓷单冠修复,随访观察2年,用改良的美国公共卫生署...目的观察瓷基台和钛基台用于种植体支持全瓷单冠修复的美观效果以及两者对种植体周围软硬组织的影响。方法 19例单颗上颌前牙缺失患者,分为瓷基台组(8例)和钛基台组(11例),行种植体支持全瓷单冠修复,随访观察2年,用改良的美国公共卫生署(United States PublicHealth Service,USPHS)标准评价两者的美观效果,并在修复后6、12、18和24个月测量种植体周围牙龈出血指数和骨吸收量,所得数据进行秩和检验和方差分析。结果在随访期间内未发现全瓷冠和钛基台折断,1例瓷基台在修复后15个月折断。瓷基台组和钛基台组达到 USPHS 标准 A 级的分别为8例和10例,差异无统计学意义(P>0.05)。种植体周围牙龈组织颜色正常,无炎性反应,瓷基台和钛基台修复2年后种植体周围骨吸收量分别为0.70 mm 和0.77 mm。统计学分析表明,瓷基台组和钛基台组两组间,以及同种基台修复后不同时间的牙龈出血指数和骨吸收量差异均无统计学意义(P>0.05)。结论瓷基台和钛基台用于种植体支持全瓷单冠修复可取得理想的美观效果,两者均对种植体周围软硬组织无明显的不良影响。展开更多
The presence of ice cover in winter can significantly change the flow field around bridge abutments, which can also cause a different local scour pattern. To investigate the impacts of ice cover, results from a recent...The presence of ice cover in winter can significantly change the flow field around bridge abutments, which can also cause a different local scour pattern. To investigate the impacts of ice cover, results from a recent flume experiments were presented. Smooth and rough ice covers were created to investigate the impacts of ice cover roughness on the scour geometry around the semi-circular abutment. Three bed materials were used, with 50D s of 0.58 mm, 0.50 mm, 0.47 mm respectively. Scour volume and scour area were calculated. It was found that the maximum scour depth was located 75o inclined to the flume wall. Under rough ice cover, the scour area and scour depth were the largest. An empirical equation on the maximum scour depth was also developed.展开更多
基金supported by the National Natural Science Foundation of China(No.51074004)the Open Project of State Key Laboratory Breeding Base for Mining Disaster Prevention and Control of Shandong University of Science and Technology of China(No.MDPC2012KF06)+1 种基金the Natural Science Foundation of Anhui Province of China(No.11040606M102)Young Teachers Science Foundation of Anhui University of Science&Technology of China(No.2012QNZ14)
文摘According to the distribution of abutment stress in a stope,this research established the mechanical model of mining abutment pressure transmission in floor base on the theory of semi-infnite plate body in elasticity.This study takes the 762 working face of Haizi Coal Mine as a case in point,and analyzed the dynamic evolution law of seam floor stress during the mining process.With an organic combination of the mining floor stress and surrounding rock stress,the study obtained the change laws of the maximum principle stress and the minimum one for the floor roadway surrounding rock when mining the upper working face.Considering the non-constant pressure force state and the cracks revolution mechanisms of floor roadway surrounding rock,the research built the mechanical model of roadway stress.Simulation results verify the reliability of the above conclusions.Moreover,this model could provide the theoretical basis and technical support for controlling floor roadway surrounding rock.
基金funded by the Science and Technology Department of Railway Ministry (Grant No. Z2012061)
文摘Abutment piles in soft ground may be subjected to both vertical and horizontal soil movements resulting from approach embankment loads. To constrain the soil movements, the soft soil ground beneath the approach embankment is often improved using composite pile foundations, which aim at mitigating the bump induced by high-speed trains passing through the bridge. So far, there is limited literature on exploring the influence of the degree of ground improvement on abutment piles installed in soft soil grounds. In this paper, a series of three-dimensional （3D） centrifuge model tests was performed on an approach embankment over a silty clay deposit improved by cement-fly ash-gravel （CFG） piles combined with geogrid. Emphasis is placed on the effects of ground replacement ratio （m） on the responses of the abutment piles induced by embankment loads. Meanwhile, a numerical study was conducted with varying ground replacement ratio of the pile-reinforced grounds. Results show that the performance of the abutment piles is significantly improved when reinforcing the ground with CFG piles beneath the approach embankment. Interestingly, there is a threshold value of the replacement ratio of around 4.9% above which the effect of CFG pile foundations is limited. This implies that it is essential to optimize the ground improvement for having a cost-effective design while minimizing the risk of the bump at the end of bridge.
基金supported by The National Natural Science Foundation of China(Grant No.51427804)National Key Technology Support Program(Grant No.2012BAF14B00)Natural Science Foundation of Anhui Province(Grant Nos.1408085MKL92,1408085MKL93)
文摘An investigation was conducted on the overall burst-instability of isolated coal pillars by means of the possibility index diagnosis method（PIDM）. First, the abutment pressure calculation model of the gob in side direction was established to derive the abutment pressure distribution curve of the isolated coal pillar. Second, the overall burst-instability ratio of the isolated coal pillars was defined. Finally, the PIDM was utilized to judge the possibility of overall burst-instability and recoverability of isolated coal pillars.The results show that an overall burst-instability may occur due to a large gob width or a small pillar width. If the width of the isolated coal pillar is not large enough, the shallow coal seam will be damaged at first, and then the high abutment pressure will be transferred to the deep coal seam, which may cause an overall burst-instability accident. This approach can be adopted to design widths of gobs and isolated coal pillars and to evaluate whether an existing isolated coal pillar is recoverable in skip-mining mines.
文摘目的观察瓷基台和钛基台用于种植体支持全瓷单冠修复的美观效果以及两者对种植体周围软硬组织的影响。方法 19例单颗上颌前牙缺失患者,分为瓷基台组(8例)和钛基台组(11例),行种植体支持全瓷单冠修复,随访观察2年,用改良的美国公共卫生署(United States PublicHealth Service,USPHS)标准评价两者的美观效果,并在修复后6、12、18和24个月测量种植体周围牙龈出血指数和骨吸收量,所得数据进行秩和检验和方差分析。结果在随访期间内未发现全瓷冠和钛基台折断,1例瓷基台在修复后15个月折断。瓷基台组和钛基台组达到 USPHS 标准 A 级的分别为8例和10例,差异无统计学意义(P>0.05)。种植体周围牙龈组织颜色正常,无炎性反应,瓷基台和钛基台修复2年后种植体周围骨吸收量分别为0.70 mm 和0.77 mm。统计学分析表明,瓷基台组和钛基台组两组间,以及同种基台修复后不同时间的牙龈出血指数和骨吸收量差异均无统计学意义(P>0.05)。结论瓷基台和钛基台用于种植体支持全瓷单冠修复可取得理想的美观效果,两者均对种植体周围软硬组织无明显的不良影响。
基金funded partially by the Research Project Awards from UNBCthe Natural Science and Engineering Research Council of Canada(NSERC)
文摘The presence of ice cover in winter can significantly change the flow field around bridge abutments, which can also cause a different local scour pattern. To investigate the impacts of ice cover, results from a recent flume experiments were presented. Smooth and rough ice covers were created to investigate the impacts of ice cover roughness on the scour geometry around the semi-circular abutment. Three bed materials were used, with 50D s of 0.58 mm, 0.50 mm, 0.47 mm respectively. Scour volume and scour area were calculated. It was found that the maximum scour depth was located 75o inclined to the flume wall. Under rough ice cover, the scour area and scour depth were the largest. An empirical equation on the maximum scour depth was also developed.
