Lake area information in the Badain Jaran Desert in 1973, 1990, 2000, and 2010 was obtained by visual interpretation and water index analysis of remote sensing images, based on the spatial and temporal characteristics...Lake area information in the Badain Jaran Desert in 1973, 1990, 2000, and 2010 was obtained by visual interpretation and water index analysis of remote sensing images, based on the spatial and temporal characteristics of lake area changes during 37 years. Results indicated that the nttmber of lakes declined from 94 to 82 and the total surface area was reduced by 3.69 km2 during 1973-2010. The desert lake area reduced by different degrees in different periods, but this occurred most rapidly during 1973-1990. According to the statistics of lake area changes, lake area decreases mainly occurred in the lakes with areas less than 0.2 km2, while the areas of lakes greater than 0.9 km2 only fluctuated. The changes of lake areas were probably due to changes in the quantity of underground water supplies rather than the effects of local climate change or human factors.展开更多
Mechanism and modeling of the land subsidence are complex because of the complicate geological background in Beijing, China. This paper analyzed the spatial relationship between land subsidence and three factors, incl...Mechanism and modeling of the land subsidence are complex because of the complicate geological background in Beijing, China. This paper analyzed the spatial relationship between land subsidence and three factors, including the change of groundwater level, the thickness of compressible sediments and the building area by using remote sensing and GIS tools in the upper-middle part of alluvial-proluvial plain fan of the Chaobai River in Beijing. Based on the spatial analysis of the land subsidence and three factors, there exist significant non-linear relationship between the vertical displacement and three factors. The Back Propagation Neural Network (BPN) model combined with Genetic Algorithm (GA) was used to simulate regional distribution of the land subsidence. Results showed that at field scale, the groundwater level and land subsidence showed a significant linear relationship. However, at regional scale, the spatial distribution of groundwater depletion funnel did not overlap with the land subsidence funnel. As to the factor of compressible strata, the places with the biggest compressible strata thickness did not have the largest vertical displacement. The distributions of building area and land subsidence have no obvious spatial relationships. The BPN-GA model simulation results illustrated that the accuracy of the trained model during fifty years is acceptable with an error of 51% of verification data less than 20 mm and the average of the absolute error about 32 mm. The BPN model could be utilized to simulate the general distribution of land subsidence in the study area. Overall, this work contributes to better understand the complex relationship between the land subsidence and three influencing factors. And the distribution of the land subsidence can be simulated by the trained BPN-GA model with the limited available dada and acceptable accuracy.展开更多
Tianjin is one of the inland cities with the most severe cases of subsidence hazard in China.The majority of the existing studies have mainly focused on Beijing-Tianjin-Hebei,and little attention has been given to Tia...Tianjin is one of the inland cities with the most severe cases of subsidence hazard in China.The majority of the existing studies have mainly focused on Beijing-Tianjin-Hebei,and little attention has been given to Tianjin.In addition,these existing studies are short-term investigations,lacking long-term monitoring of surface subsidence.In the present study,we use the Small Baseline Subset Interferometric Synthetic Aperture Radar(SBAS-InSAR)technique to monitor the subsidence process in Tianjin between 2015 and 2020 and reveal its spatial and temporal variation.We divided the 44-view Sentinel-1A image data into three periods to avoid the effect of temporal and spatial decoherence by extracting the surface deformation field in Tianjin.We finally verified the accuracy and reliability of the inversion results using second-order leveling data.Results showed that the correlation coefficient r between the two reached 0.89,and the root mean square error was 4.84 mm/y.Obvious subsidence funnels exist in Tianjin,mainly in the towns of Wangqingtuo and Shengfang.These subsidence funnels have a subsidence deformation rate of-136.2 mm/y and a maximum cumulative settlement of-346.3 mm within the study period.The subsidence area tends to extend to the southwest.The analysis of annual rainfall,groundwater resource extraction,spatial location distribution of industrial areas combined with SBAS-InSAR inversion results indicates that overextraction of groundwater resources is the main cause of land subsidence in the area.Therefore,strict control of groundwater extraction is the main approach to mitigate land subsidence effectively.展开更多
Groundwater level change stands a momentous role in affecting the geotechnical construction stability and safety of underground structures.Global warming and active underground construction cause conspicuous changes i...Groundwater level change stands a momentous role in affecting the geotechnical construction stability and safety of underground structures.Global warming and active underground construction cause conspicuous changes in the groundwater level,which further leaves an impact on the underground structures’serviceability.To reveal the interaction between underground structure and soil under groundwater level change in the sand layer,model tests of circular transportation tunnel and rectangular utility tunnel were carried out.With the self-designed experimental equipment and innovative experimental methods,the changes in tunnel stress,bending moment,buoyancy,and vertical displacement of the rise and drawdown of the groundwater level in the sand layer were studied.The results revealed the developments of concentrated structural forces during the rising and falling process of the groundwater water level,indi-cating critical locations that should be strengthened.Meanwhile,both tunnels showed the same movement trend:settling first,floating afterwards and settling at last.And it is concluded that no reduction is required when calculating buoyancy in sands using measured pore pressure.Conclusions can provide a notable reference for future related research and engineering designs.展开更多
基金supported by the National Natural Science Foundation of China(41371114,41101187)the National Environmental Protection Public Welfare Industry Tar-geted Research Fund(201209034)the Ministry of Education,Humanities and Social Science Projects(10YJCZH053)
文摘Lake area information in the Badain Jaran Desert in 1973, 1990, 2000, and 2010 was obtained by visual interpretation and water index analysis of remote sensing images, based on the spatial and temporal characteristics of lake area changes during 37 years. Results indicated that the nttmber of lakes declined from 94 to 82 and the total surface area was reduced by 3.69 km2 during 1973-2010. The desert lake area reduced by different degrees in different periods, but this occurred most rapidly during 1973-1990. According to the statistics of lake area changes, lake area decreases mainly occurred in the lakes with areas less than 0.2 km2, while the areas of lakes greater than 0.9 km2 only fluctuated. The changes of lake areas were probably due to changes in the quantity of underground water supplies rather than the effects of local climate change or human factors.
基金Under the auspices of National Natural Science Foundation of China(No.41201420,41130744)Beijing Nova Program(No.Z111106054511097)Foundation of Beijing Municipal Commission of Education(No.KM201110028016)
文摘Mechanism and modeling of the land subsidence are complex because of the complicate geological background in Beijing, China. This paper analyzed the spatial relationship between land subsidence and three factors, including the change of groundwater level, the thickness of compressible sediments and the building area by using remote sensing and GIS tools in the upper-middle part of alluvial-proluvial plain fan of the Chaobai River in Beijing. Based on the spatial analysis of the land subsidence and three factors, there exist significant non-linear relationship between the vertical displacement and three factors. The Back Propagation Neural Network (BPN) model combined with Genetic Algorithm (GA) was used to simulate regional distribution of the land subsidence. Results showed that at field scale, the groundwater level and land subsidence showed a significant linear relationship. However, at regional scale, the spatial distribution of groundwater depletion funnel did not overlap with the land subsidence funnel. As to the factor of compressible strata, the places with the biggest compressible strata thickness did not have the largest vertical displacement. The distributions of building area and land subsidence have no obvious spatial relationships. The BPN-GA model simulation results illustrated that the accuracy of the trained model during fifty years is acceptable with an error of 51% of verification data less than 20 mm and the average of the absolute error about 32 mm. The BPN model could be utilized to simulate the general distribution of land subsidence in the study area. Overall, this work contributes to better understand the complex relationship between the land subsidence and three influencing factors. And the distribution of the land subsidence can be simulated by the trained BPN-GA model with the limited available dada and acceptable accuracy.
基金Natural Science Foundation of Guangxi(Nos.2018GXNSFBA050006,2020GXNSFBA159033)Wuhan Science and Technology Plan Project(No.2019010702011314)+2 种基金Guangxi Science and Technology Plan Project(No.GUIKE AD19110107)National Natural Science Foundation of China(Nos.42064003,42064002)Guangxi Universities Young and Middle-aged Teachers’Basic Scientific Research Ability Improvement Project(No.2020KY0603)。
文摘Tianjin is one of the inland cities with the most severe cases of subsidence hazard in China.The majority of the existing studies have mainly focused on Beijing-Tianjin-Hebei,and little attention has been given to Tianjin.In addition,these existing studies are short-term investigations,lacking long-term monitoring of surface subsidence.In the present study,we use the Small Baseline Subset Interferometric Synthetic Aperture Radar(SBAS-InSAR)technique to monitor the subsidence process in Tianjin between 2015 and 2020 and reveal its spatial and temporal variation.We divided the 44-view Sentinel-1A image data into three periods to avoid the effect of temporal and spatial decoherence by extracting the surface deformation field in Tianjin.We finally verified the accuracy and reliability of the inversion results using second-order leveling data.Results showed that the correlation coefficient r between the two reached 0.89,and the root mean square error was 4.84 mm/y.Obvious subsidence funnels exist in Tianjin,mainly in the towns of Wangqingtuo and Shengfang.These subsidence funnels have a subsidence deformation rate of-136.2 mm/y and a maximum cumulative settlement of-346.3 mm within the study period.The subsidence area tends to extend to the southwest.The analysis of annual rainfall,groundwater resource extraction,spatial location distribution of industrial areas combined with SBAS-InSAR inversion results indicates that overextraction of groundwater resources is the main cause of land subsidence in the area.Therefore,strict control of groundwater extraction is the main approach to mitigate land subsidence effectively.
基金the financial support from National Major Scientific Instruments Development Project of China(Grant no.5202780029)High-end Foreign Expert Introduction program(No.DL2021165001L)Science and Technology Research Program of Chongqing Municipal Education Commission(No.KJCXZD2020002).
文摘Groundwater level change stands a momentous role in affecting the geotechnical construction stability and safety of underground structures.Global warming and active underground construction cause conspicuous changes in the groundwater level,which further leaves an impact on the underground structures’serviceability.To reveal the interaction between underground structure and soil under groundwater level change in the sand layer,model tests of circular transportation tunnel and rectangular utility tunnel were carried out.With the self-designed experimental equipment and innovative experimental methods,the changes in tunnel stress,bending moment,buoyancy,and vertical displacement of the rise and drawdown of the groundwater level in the sand layer were studied.The results revealed the developments of concentrated structural forces during the rising and falling process of the groundwater water level,indi-cating critical locations that should be strengthened.Meanwhile,both tunnels showed the same movement trend:settling first,floating afterwards and settling at last.And it is concluded that no reduction is required when calculating buoyancy in sands using measured pore pressure.Conclusions can provide a notable reference for future related research and engineering designs.
