Most tunnel projects are designed with cross-sectional loads,and the inhomogeneity of the longitudinal forces is ignored.In theory,such a support structure can resist large loads,but in practice,large deformation,conc...Most tunnel projects are designed with cross-sectional loads,and the inhomogeneity of the longitudinal forces is ignored.In theory,such a support structure can resist large loads,but in practice,large deformation,concrete cracking,steel frame distortion,and other phenomena often occur in tunnels under poor surrounding rock conditions.Hence,the longitudinal stability of the tunnel must be considered.In this study,the mechanism of longitudinal connecting ribs(LCRs)of tunnels was investigated through element tests,theoretical analyses,and numerical simulations,and the effect of the LCRs was evaluated experimentally.The applicability of the constitutive relations and boundary conditions of the numerical model was verified.The instability mode of the steel frame reflecting the longitudinal stress gradient of the tunnel was analyzed,and the longitudinal surrounding rock pressure and the verified numerical model were applied to analyze the LCR using the load structure method.The results indicate the following:(1)LCRs can effectively improve the ultimate bearing capacity and stability of a structure and reduce the area and degree of damage;(2)Two types of instability modes occur in tunnel steel frames,and the main factor is bending failure caused by the axial force;(3)The distance sensitivity of the LCR in the tunnel is higher than the stiffness sensitivity.For large deformations of tunnels,double rows of rebars with a spacing of less than 1.5 m should be used as longitudinal connections.展开更多
The agricultural and livestock activities surrounding the rivers flowing into the lakes have caused non-point source pollution, leading to excessive amounts of nutrient salts in downstream rivers. Introducing river wa...The agricultural and livestock activities surrounding the rivers flowing into the lakes have caused non-point source pollution, leading to excessive amounts of nutrient salts in downstream rivers. Introducing river water into constructed wetlands along river course has proven to be an effective solution for decreasing nitrogen(N) and phosphorus(P) loads. This paper reports 9 years of monitoring the Yong’an River and its surrounding constructed wetlands in the upper reaches of Erhai Lake, located in Yunnan Province, China. This study analyzed the main types of pollutants in the river, and evaluated the removal efficiency of pollutants by the constructed wetlands. The findings indicate that total nitrogen(TN) and nitrate nitrogen(NO_(3)^(–)-N) are the primary pollutants in the Yong’an River, which exhibit variation throughout the year corresponding to the alternating wet and dry seasons. Although constructed wetlands are effective in removing NO_(3)^(-)-N and P, their efficacy in removing ammonium nitrogen(NH_(4)^(+)-N)and organic pollutants is limited. This limitation can be attributed to the lack of timely disposal of aquatic plant residues. This research contributes to the understanding of the potential issues that may arise during the extended use of constructed wetlands and provides solutions to address them.展开更多
基金supported by the Major Project of Science and Technology Research and Development Plan of China Railway Corporation(2017G006-B)High-Speed Rail Joint-Fund Funded Projects(U1934213).
文摘Most tunnel projects are designed with cross-sectional loads,and the inhomogeneity of the longitudinal forces is ignored.In theory,such a support structure can resist large loads,but in practice,large deformation,concrete cracking,steel frame distortion,and other phenomena often occur in tunnels under poor surrounding rock conditions.Hence,the longitudinal stability of the tunnel must be considered.In this study,the mechanism of longitudinal connecting ribs(LCRs)of tunnels was investigated through element tests,theoretical analyses,and numerical simulations,and the effect of the LCRs was evaluated experimentally.The applicability of the constitutive relations and boundary conditions of the numerical model was verified.The instability mode of the steel frame reflecting the longitudinal stress gradient of the tunnel was analyzed,and the longitudinal surrounding rock pressure and the verified numerical model were applied to analyze the LCR using the load structure method.The results indicate the following:(1)LCRs can effectively improve the ultimate bearing capacity and stability of a structure and reduce the area and degree of damage;(2)Two types of instability modes occur in tunnel steel frames,and the main factor is bending failure caused by the axial force;(3)The distance sensitivity of the LCR in the tunnel is higher than the stiffness sensitivity.For large deformations of tunnels,double rows of rebars with a spacing of less than 1.5 m should be used as longitudinal connections.
基金supported by National Key Research and Development Program of China(2021YFD1700400)Yunnan Fundamental Research Projects(202201AU070001)Startup Fund for Young Faculty at SJTU(22X010500256).
文摘The agricultural and livestock activities surrounding the rivers flowing into the lakes have caused non-point source pollution, leading to excessive amounts of nutrient salts in downstream rivers. Introducing river water into constructed wetlands along river course has proven to be an effective solution for decreasing nitrogen(N) and phosphorus(P) loads. This paper reports 9 years of monitoring the Yong’an River and its surrounding constructed wetlands in the upper reaches of Erhai Lake, located in Yunnan Province, China. This study analyzed the main types of pollutants in the river, and evaluated the removal efficiency of pollutants by the constructed wetlands. The findings indicate that total nitrogen(TN) and nitrate nitrogen(NO_(3)^(–)-N) are the primary pollutants in the Yong’an River, which exhibit variation throughout the year corresponding to the alternating wet and dry seasons. Although constructed wetlands are effective in removing NO_(3)^(-)-N and P, their efficacy in removing ammonium nitrogen(NH_(4)^(+)-N)and organic pollutants is limited. This limitation can be attributed to the lack of timely disposal of aquatic plant residues. This research contributes to the understanding of the potential issues that may arise during the extended use of constructed wetlands and provides solutions to address them.
