Monitoring Three-Dimensional Displacements Of Open-Pit Mine Slopes By Incorporating InSAR With Spatial Moving Characteristics

Open-pit mining would disturb the original stress balance of surrounding rock mass,potentially causing geological disasters such as landslides or collapses of slope.Since surface displacement is an important indicator to identify mining-related geohazards,it is important to monitor surface displacements over open-pit mines and further analyze the spatiotemporal evolution.Interferometric Synthetic Aperture Radar(InSAR)technique has been widely used in open-pit mine slopes displacements monitoring at present,owing to its advantages of all-time,all-weather,wide coverage,and so on.However,it is challenging to reveal the real deformation pattern of open pit slopes from one-dimensional displacements of single-track InSAR measurements,dramatically hindering the application scope of InSAR.Existing InSAR three-dimensional displacements monitoring methods have different limitations when applied to open-pit mine slopes.For example,the multi-track InSAR fusion method for retrieving threedimensional displacements has a stringent requirement on SAR images,and the accuracy of the retrieved north-south movements is poor.Consequently,it is difficult to reliably identify landslide risks of open pit mines with InSAR.To circumvent the limitation,we proposed a new method to monitor three-dimensional displacements of open-pit mine slopes by incorporating InSAR with spatial moving characteristics in this paper.Theoretically,the introduction of prior information can reduce the requirements on SAR data that InSAR three-dimensional displacements solution needs,and improve the accuracy of north-south solution which is poor caused by the current polar flight orbit of SAR satellites.In order to apply this method to large area,this paper introduced the concept of slope angle of open-pit mine,and proposed a three-dimensional displacements monitoring method for openpit mine slopes in a large area.The main contents and innovations of this paper are as follows:(1)A new three-dimensional displacements monitoring method for open-pit mine slopes was proposed.Firstly,a prior constraint was constructed based on the prior knowledge that slopes in open-pit mine horizontally moves towards the aspect direction in theory.Then,a functional model involving the prior constraint and three-dimensional displacements of open-pit mine slope was created,according to the projection of three-dimensional displacements onto SAR line of sight direction.Thirdly,three-dimensional displacements of open-pit mine slopes were solved based on the function model.In addition,simulation experiments demonstrated that the accuracy of the north-south displacements monitored by the proposed model is higher than that of the multi-track InSAR fusion method.Finally,this paper took the slope of an open-pit mine in Fuxin City,Liaoning Province as the research area,and the results show that the accuracy of three-dimensional displacements is about 1.2 cm,occupying 5.6% of the maximum displacements,indicating that the three-dimensional deformation field of open-pit mine slope solved by the method proposed in this paper is reliable.(2)A method combined space-borne optical photogrammetry and InSAR to monitor three-dimensional displacements of open-pit mine slopes in large area was proposed.Firstly,the DEM of the study area was generated based on satellite optical stereo images,and the slope of the area was calculated.Then,according to the numerical characteristics of the slope angle of the open-pit mine,the identification threshold was established to extract the open-pit mine slopes in study area.Finally,the method of combining InSAR and aspect constraint was used to solve the three-dimensional displacements of the identified slope,and realized the three-dimensional displacements monitoring of the open-pit mine slopes in a large area.In order to verify the application potential of the proposed method in engineering practice,this paper selected the Xinqiu mining area in Fuxin City,Liaoning Province as the study area.This mining area is a demonstration area for comprehensive treatment of abandoned mining areas in China.Currently,it is striving to become a Centennial International Circuit City through industrial transformation and upgrading.The results showed that during the period from December 2020 to October 2021,the slopes of 1# pit,the northeast and southwest slopes of 3# pit,the east and west slopes of 4# pit,and the northeast and the southwest slopes of 5# pit had great displacements,which were potential geological hazards.In addition,by analyzing the three-dimensional time series displacements process curve of each slope and the daily rainfall data in the study area,most of the displacements characteristics of these slopes are closely related to rainfall during the monitoring period.With the increase of rainfall,the displacements velocity of slopes accelerates.Under the heavy rain and rainstorm,some slopes even have accelerated displacements for many times.The proposed method in this paper is beneficial to improve the accuracy of InSAR-based three-dimensional displacements of open-pit mine,and further to enhance the ability to identify potential landslides in open-pit mine slope.