The first permanent magnet driven rectangular pipe jacking machine independently developed in China is used for the construction of pedestrian passage in Banxuegang Science and Technology City area of Shenzhen. The re...The first permanent magnet driven rectangular pipe jacking machine independently developed in China is used for the construction of pedestrian passage in Banxuegang Science and Technology City area of Shenzhen. The rectangular pipe jacking machine occupies a small area during the initial excavation. It is suitable for shallow soil covering and short-distance excavation. It is more economical and applicable than shield machine and has high construction efficiency. During the construction process, technical measures such as attitude measurement and adjustment of pipe jacking machine, surrounding rock grouting and friction reduction can effectively ensure the smooth construction of pipe jacking machine, and provide reference for large section pipe jacking machine in shallow soil construction.展开更多
It is inevitable to cut reinforced concrete(RC)appeared in cross passage of city metro by cutting tools when constructing in densely populated area.The previous cutters employed to cut RC are insufficient and easily d...It is inevitable to cut reinforced concrete(RC)appeared in cross passage of city metro by cutting tools when constructing in densely populated area.The previous cutters employed to cut RC are insufficient and easily damaged,so a new polycrystalline diamond compact(PDC)cutter is used to solve this question.Based on the theoretical analysis of cutting mechanism,both circular and tapered PDC cutters with cutting edge angle of 90and negative front rack angle of 10are used to cut RC.The peeling and breaking patterns of cutting concrete are proposed,the nodular and grainy chips are the preferred modes in cutting steel bars.The LS-DYNA is employed to investigate the cutting performance in advance.The simulation results show that the average and peak cutting forces increase with the growth of penetration depth,cutting speed,and roundness,and subsequently the recommended penetration depth less than 1.2 mm is obtained to cut RC due to the existence of steel bars.Moreover,the linear cutting platform is adopted to investigate the force ability and damage state of PDC cutters.It is concluded that the cutting force increases abruptly and fluctuates heavily when cutting the coarse aggregates.The patterns occurred in both numerical and experimental results are generally similar.Notably,the steel bar is pulled out and the PDC cutter is damaged at the penetration depth of 0.8 mm,while a good cut occurs at the penetration depth of 0.3 mm.The tapered PDC cutter with a relatively low cutting force is prone to be broken compared with circular PDC cutter.It is suggested that the circular PDC cutter at the penetration depth of 0.3 mm should be used to cut RC in practical engineering.展开更多
文摘The first permanent magnet driven rectangular pipe jacking machine independently developed in China is used for the construction of pedestrian passage in Banxuegang Science and Technology City area of Shenzhen. The rectangular pipe jacking machine occupies a small area during the initial excavation. It is suitable for shallow soil covering and short-distance excavation. It is more economical and applicable than shield machine and has high construction efficiency. During the construction process, technical measures such as attitude measurement and adjustment of pipe jacking machine, surrounding rock grouting and friction reduction can effectively ensure the smooth construction of pipe jacking machine, and provide reference for large section pipe jacking machine in shallow soil construction.
基金supported by the Shanghai Science and Technology Development Funds(Grant No.20QB1401800)Xuzhou Science and Technology Plan Social Development Key Special Project(Grant No.SHFZZDZX20210017)Yunlong Lake Laboratory of Deep Underground Science and Engineering Project(Grant No.104023006).
文摘It is inevitable to cut reinforced concrete(RC)appeared in cross passage of city metro by cutting tools when constructing in densely populated area.The previous cutters employed to cut RC are insufficient and easily damaged,so a new polycrystalline diamond compact(PDC)cutter is used to solve this question.Based on the theoretical analysis of cutting mechanism,both circular and tapered PDC cutters with cutting edge angle of 90and negative front rack angle of 10are used to cut RC.The peeling and breaking patterns of cutting concrete are proposed,the nodular and grainy chips are the preferred modes in cutting steel bars.The LS-DYNA is employed to investigate the cutting performance in advance.The simulation results show that the average and peak cutting forces increase with the growth of penetration depth,cutting speed,and roundness,and subsequently the recommended penetration depth less than 1.2 mm is obtained to cut RC due to the existence of steel bars.Moreover,the linear cutting platform is adopted to investigate the force ability and damage state of PDC cutters.It is concluded that the cutting force increases abruptly and fluctuates heavily when cutting the coarse aggregates.The patterns occurred in both numerical and experimental results are generally similar.Notably,the steel bar is pulled out and the PDC cutter is damaged at the penetration depth of 0.8 mm,while a good cut occurs at the penetration depth of 0.3 mm.The tapered PDC cutter with a relatively low cutting force is prone to be broken compared with circular PDC cutter.It is suggested that the circular PDC cutter at the penetration depth of 0.3 mm should be used to cut RC in practical engineering.
