Land subsidence is a major factor that affects metro line （ML） stability. In this study, an improved multi- temporal interferometric synthetic aperture radar （InSAR） （MTI） method to detect land subsidence near M...Land subsidence is a major factor that affects metro line （ML） stability. In this study, an improved multi- temporal interferometric synthetic aperture radar （InSAR） （MTI） method to detect land subsidence near MLs is presented. In particular, our multi-temporal InSAR method provides surface subsidence measurements with high observation density. The MTI method tracks both point-like targets and distributed targets with temporal radar back- scattering steadiness. First, subsidence rates at the point targets with low-amplitude dispersion index （ADI） values are extracted by applying a least-squared estimator on an optimized freely connected network. Second, to reduce error propagation, the pixels with high-ADI values are classified into several groups according to ADI intervals and processed using a Pearson correlation coefficient and hierarchical analysis strategy to obtain the distributed targets. Then, nonlinear subsidence components at all point-like and distributed targets are estimated using phase unwrapping and spatiotemporal filtering on the phase residuals. The proposed MTI method was applied to detect land subsidence near MLs of No. 1 and 3 in the Baoshan district of Shanghai using 18 TerraSAR-X images acquired between April 21, 2008 and October 30, 2010. The results show that the mean subsidence rates of the stations distributed along the two MLs are -12.9 and -14.0 ram/year. Furthermore, three subsidence funnels near the MLs are discovered through the hierarchical analysis. The testing results demonstrate the satisfactory capacity of the proposed MTI method in providing detailed subsidence information near MLs.展开更多
Though a comprehensive in situ measurement project,the performance of a deep pit-in-pit excavation constructed by the top-down method in seasonal frozen soil area in Shenyang was extensively examined.The measured exca...Though a comprehensive in situ measurement project,the performance of a deep pit-in-pit excavation constructed by the top-down method in seasonal frozen soil area in Shenyang was extensively examined.The measured excavation responses included the displacement of capping beam and retaining pile,settlement of ground surface,and deformation of metro lines.Based on the analyses of field data,some major findings were obtained:1)the deformations of retaining structures fluctuated along with the increase of temperature,2)the deformation variation of retaining structures after the occurrence of thawing of seasonal frozen soil was greater than that in winter,although the excavation depth was smaller than before,3)the influence area of ground settlement was much smaller because of the features of seasonal frozen sandy soil,4)the displacement of metro line showed a significant spatial effect,and the tunnel lining had an obviously hogging displacement pattern,and 5)earth pressure redistribution occurred due to the combined effects of freezing-thawing of seasonal frozen soil and excavation,leading to the deformation of metro line.The influence area of ground settlement was obviously smaller than that of Shanghai soft clay or other cases reported in literatures because of special geological conditions of Shenyang.However,the deformation of metro lines was significantly lager after the thawing of the frozen soil,the stress in deep soil was redistributed,and the metro lines were forced to deform to meet a new state of equilibrium.展开更多
文摘Land subsidence is a major factor that affects metro line （ML） stability. In this study, an improved multi- temporal interferometric synthetic aperture radar （InSAR） （MTI） method to detect land subsidence near MLs is presented. In particular, our multi-temporal InSAR method provides surface subsidence measurements with high observation density. The MTI method tracks both point-like targets and distributed targets with temporal radar back- scattering steadiness. First, subsidence rates at the point targets with low-amplitude dispersion index （ADI） values are extracted by applying a least-squared estimator on an optimized freely connected network. Second, to reduce error propagation, the pixels with high-ADI values are classified into several groups according to ADI intervals and processed using a Pearson correlation coefficient and hierarchical analysis strategy to obtain the distributed targets. Then, nonlinear subsidence components at all point-like and distributed targets are estimated using phase unwrapping and spatiotemporal filtering on the phase residuals. The proposed MTI method was applied to detect land subsidence near MLs of No. 1 and 3 in the Baoshan district of Shanghai using 18 TerraSAR-X images acquired between April 21, 2008 and October 30, 2010. The results show that the mean subsidence rates of the stations distributed along the two MLs are -12.9 and -14.0 ram/year. Furthermore, three subsidence funnels near the MLs are discovered through the hierarchical analysis. The testing results demonstrate the satisfactory capacity of the proposed MTI method in providing detailed subsidence information near MLs.
基金National Natural Science Foundation of China(Grant No.52108380)Natural Science Foundation of Jiangsu Province of China(No.BK20210721)Natural Science Foundation of Jiangsu Province of China(No.BK20230500).
文摘Though a comprehensive in situ measurement project,the performance of a deep pit-in-pit excavation constructed by the top-down method in seasonal frozen soil area in Shenyang was extensively examined.The measured excavation responses included the displacement of capping beam and retaining pile,settlement of ground surface,and deformation of metro lines.Based on the analyses of field data,some major findings were obtained:1)the deformations of retaining structures fluctuated along with the increase of temperature,2)the deformation variation of retaining structures after the occurrence of thawing of seasonal frozen soil was greater than that in winter,although the excavation depth was smaller than before,3)the influence area of ground settlement was much smaller because of the features of seasonal frozen sandy soil,4)the displacement of metro line showed a significant spatial effect,and the tunnel lining had an obviously hogging displacement pattern,and 5)earth pressure redistribution occurred due to the combined effects of freezing-thawing of seasonal frozen soil and excavation,leading to the deformation of metro line.The influence area of ground settlement was obviously smaller than that of Shanghai soft clay or other cases reported in literatures because of special geological conditions of Shenyang.However,the deformation of metro lines was significantly lager after the thawing of the frozen soil,the stress in deep soil was redistributed,and the metro lines were forced to deform to meet a new state of equilibrium.
