The Impact Of Groundwater Level Fluctuation On Loess Landslide Deformation

Due to the long-term arid and rainless conditions in the Loess Plateau,irrigation is necessary for agricultural development in the loess terrace.However,the infiltration of irrigation water has caused the groundwater level to rise,resulting in a large number of loess landslides along the edges of the loess terrace.Heifangtai is known as a"natural experimental site for loess landslides,"and the extensive loess landslides caused by the rising groundwater level due to long-term irrigation have resulted in several casualties and have constrained local economic development.Therefore,studying the impact of long-term groundwater level fluctuations on loess landslides in the entire Heitai region is of great significance.This study is based on hydrogeological conditions in the study area and survey data collected from irrigation,rainfall,excretion,and borehole monitoring.It comprehensively applies Visual Modflow software and high-density electrical resistivity imaging to obtain the changes in groundwater level from 2015 to 2021 in the study area.SBAS-InSAR technology with millimeter-level accuracy and weather independence is used to analyze the deformation of the Heitai from 2015 to 2021.Based on the results of both,the groundwater level change curve and cumulative deformation in the deformation area of the plateau slope were extracted.Time series analysis and correlation analysis were conducted on the two,and the number and type of landslides before and after irrigation cessation were investigated.Combining multi-source remote sensing methods,discuss the impact of groundwater level changes on loess landslides in the study area,and speculate on the possibility of subsequent landslides.This study comprehensively analyzed the impact of groundwater level on the deformation of loess landslides before and after the cessation of flood irrigation in the Heitai area at a regional scale through engineering geological survey,geophysical exploration,numerical simulation,and remote sensing technology.It is of great significance for the formation mechanism,monitoring,warning,and prevention of loess landslides.This paper achieved the following three main research results:(1)Groundwater numerical simulation was used to obtain the temporal changes in the groundwater level from 2014 to 2021 in the Heitai area.The monitoring well data and electrical resistivity imaging method were used to validate the simulation results.The simulation results were relatively accurate,showing an overall trend of first rising then falling groundwater levels.From 2015 to 2019,the groundwater level increased by approximately 3.6 meters,and from 2019 to 2021,the groundwater level decreased by approximately 2.1 meters.The groundwater elevation is highest in Zhuwang Village and lowest in the northeast corner of Heitai.(2)From 2015 to 2021,the deformation rate of the edge zone of Heitai was relatively high,and most of them were located behind the landslide group,with a maximum deformation rate of-146 mm/yr,located near the Moshigou landslide group,with an area of about 0.56 km~2.The maximum cumulative deformation of deformation area 8 near the Moshigou landslide group,deformation area 7 near the Chenjia landslide group,deformation area 6 in the northeast part of the Heitai,and deformation area 4 near the Yehu ditch landslide group exceeded 300 mm,with an average annual deformation rate of more than 54 mm/yr in the two areas with the largest groundwater discharge in the north and east of the Heitai.(3)After irrigation was stopped in August 2019,the groundwater level fell,and the overall slope deformation rate was slightly lower than before.There was a good correlation between the changes in groundwater level and cumulative deformation,indicating that groundwater level is the main cause of slope deformation.62 landslides occurred before the cessation of irrigation in Heitai,and 15 landslides occurred after the cessation of irrigation,including 76 loess landslides and 1 loess bedrock landslide.The annual frequency of landslides before the cessation of irrigation was 14.31,and after the cessation of irrigation was 6.43.The frequency of landslides significantly decreased after the cessation of irrigation,indicating that the cessation of irrigation measures is more effective in controlling loess landslides in the Loess Plateau area.As time goes by,the stability of the slopes along the plateau gradually increases.Based on the results of temporal and correlation analyses,it is predicted that there is a higher probability of subsequent landslides occurring in Yehu ditch,Moshigou,and Jiaojia landslide groups.