A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field m...A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field model using more different truncated solid conical blocks to clarify the multiblock failure mechanism.Furthermore,the shape of blocks between the failure surface and the tunnel face was considered as an entire circle,and the supporting pressure was assumed as non-uniform distribution on the tunnel face and increased with the tunnel embedded depth.The ground surface settlements and failure mechanism above large-diameter shield tunnels were also investigated under different supporting pressures by the finite difference method.展开更多
In large-diameter shield tunnels,applying the double-layer lining structure can improve the load-bearing properties and maintain the stability of segmental lining.The secondary lining thickness is a key parameter in t...In large-diameter shield tunnels,applying the double-layer lining structure can improve the load-bearing properties and maintain the stability of segmental lining.The secondary lining thickness is a key parameter in the design of a double lining structure,which is worth being explored.Based on an actual large-diameter shield tunnel,loading model tests are carried out to investigate the effect of the secondary lining thickness on the mechanical behaviours of the double lining structure.The test results show that within the range of secondary lining thicknesses discussed,the load-bearing limit of the double-layer lining increases with growing secondary lining thickness.As a passive support,the secondary lining acts as an auxiliary load-bearing structure by contacting the segment.And changes in secondary lining thickness have a significant effect on the contact state between the segment and secondary lining,with both the contact pressure level and the contact area between the two varying.For double-layer lining structures in large-diameter shield tunnels,it is proposed that the stiffness of the secondary lining needs to be matched to the stiffness of the segment,as this allows them to have a coordinated deformation and a good joint load-bearing effect.展开更多
An analysis of the stability of large-diameter circular tunnels and ground settlement during tunnelling by a pressurized shield was presented. An innovative three-dimensional translational multi-block failure mechanis...An analysis of the stability of large-diameter circular tunnels and ground settlement during tunnelling by a pressurized shield was presented. An innovative three-dimensional translational multi-block failure mechanism was proposed to determine the face support pressure of large-shield tunnelling. Compared with the currently available mechanisms, the proposed mechanism has two unique features:(1) the supporting pressure applied to the tunnel face is assumed to have a non-uniform rather than uniform distribution, and(2) the method takes into account the entire circular excavation face instead of merely an inscribed ellipse. Based on the discrete element method, a numerical simulation of the Shanghai Yangtze River Tunnel was carried out using the Particle Flow Code in two dimensions. The immediate ground movement during excavation, as well as the behaviour of the excavation face, the shield movement, and the excavated area, was considered before modelling the excavation process.展开更多
Space radiation has been identified as the main health hazard to crews involved in manned Mars missions.Active shielding is more effective than passive shielding to the very energetic particles from cosmic rays.Partic...Space radiation has been identified as the main health hazard to crews involved in manned Mars missions.Active shielding is more effective than passive shielding to the very energetic particles from cosmic rays.Particle motion in a magnetic field is studied based on the single-particle theory and Monte Carlo method.By comparing the shielding efficiency of different magnetic field configurations,a novel active magnetic shielding configuration with lower mass cost and power consumption is proposed for manned Mars missions.The new magnetic configuration can shield 92.8%of protons and 84.4%of alpha particles with E<4 GeV·n^(-1),when considering the passive shielding contribution of 10.0 g·cm^(-2) Al Shielding,the required magnetic stiffness can be reduced from 27 Tm to 16 Tm.The detailed analysis of mass cost and power consumption shows that active shielding will be a promising means to protect crews from space radiation exposure in manned Mars missions.展开更多
基金Project(41202220) supported by the National Natural Science Foundation of ChinaProject(2011YYL034) supported by the Fundamental Research Funds for the Central Universities,China
文摘A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field model using more different truncated solid conical blocks to clarify the multiblock failure mechanism.Furthermore,the shape of blocks between the failure surface and the tunnel face was considered as an entire circle,and the supporting pressure was assumed as non-uniform distribution on the tunnel face and increased with the tunnel embedded depth.The ground surface settlements and failure mechanism above large-diameter shield tunnels were also investigated under different supporting pressures by the finite difference method.
基金supported by the National Natural Science Foundation of China(Grant Nos.52178398,51991394,and 51278424).
文摘In large-diameter shield tunnels,applying the double-layer lining structure can improve the load-bearing properties and maintain the stability of segmental lining.The secondary lining thickness is a key parameter in the design of a double lining structure,which is worth being explored.Based on an actual large-diameter shield tunnel,loading model tests are carried out to investigate the effect of the secondary lining thickness on the mechanical behaviours of the double lining structure.The test results show that within the range of secondary lining thicknesses discussed,the load-bearing limit of the double-layer lining increases with growing secondary lining thickness.As a passive support,the secondary lining acts as an auxiliary load-bearing structure by contacting the segment.And changes in secondary lining thickness have a significant effect on the contact state between the segment and secondary lining,with both the contact pressure level and the contact area between the two varying.For double-layer lining structures in large-diameter shield tunnels,it is proposed that the stiffness of the secondary lining needs to be matched to the stiffness of the segment,as this allows them to have a coordinated deformation and a good joint load-bearing effect.
基金Project(41202220)supported by the National Natural Science Foundation of ChinaProject(20120022120003)supported by the Research Fund for the Doctoral Program of Higher Education,China+1 种基金Project(2652012065)supported by the Fundamental Research Funds for the Central Universities of ChinaProject(2013006)supported by the Research Fund for Key Laboratory on Deep GeoDrilling Technology from the Ministry of Land and Resources of China
文摘An analysis of the stability of large-diameter circular tunnels and ground settlement during tunnelling by a pressurized shield was presented. An innovative three-dimensional translational multi-block failure mechanism was proposed to determine the face support pressure of large-shield tunnelling. Compared with the currently available mechanisms, the proposed mechanism has two unique features:(1) the supporting pressure applied to the tunnel face is assumed to have a non-uniform rather than uniform distribution, and(2) the method takes into account the entire circular excavation face instead of merely an inscribed ellipse. Based on the discrete element method, a numerical simulation of the Shanghai Yangtze River Tunnel was carried out using the Particle Flow Code in two dimensions. The immediate ground movement during excavation, as well as the behaviour of the excavation face, the shield movement, and the excavated area, was considered before modelling the excavation process.
基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDA17010301)。
文摘Space radiation has been identified as the main health hazard to crews involved in manned Mars missions.Active shielding is more effective than passive shielding to the very energetic particles from cosmic rays.Particle motion in a magnetic field is studied based on the single-particle theory and Monte Carlo method.By comparing the shielding efficiency of different magnetic field configurations,a novel active magnetic shielding configuration with lower mass cost and power consumption is proposed for manned Mars missions.The new magnetic configuration can shield 92.8%of protons and 84.4%of alpha particles with E<4 GeV·n^(-1),when considering the passive shielding contribution of 10.0 g·cm^(-2) Al Shielding,the required magnetic stiffness can be reduced from 27 Tm to 16 Tm.The detailed analysis of mass cost and power consumption shows that active shielding will be a promising means to protect crews from space radiation exposure in manned Mars missions.
