Monitoring And Prediction Of Landslides Based On GNSS

The GNSS technology applied in the stability of landslide monitoring system,the main process is precisely for a long time to determine the information of surface displacement of landslide monitoring and information through data transmission,real-time and accurately send data processing center,through the analysis of the data processing center,contrast,forecast trends,implementation of landslide forecast warning.Taking a landslide in east Lanzhou as the main research object and referring to typical landslide cases at home and abroad,this paper systematically studied the application of GNSS in landslide stability monitoring,the layout of landslide GNSS monitoring network,and the design and application of automatic landslide monitoring and prediction system.The main research contents are as follows:(1)GNSS technology is used for high-precision positioning,and carrier phase observation is usually adopted.However,in high-precision positioning by carrier phase observation,due to the existence of cycle slip and the whole cycle ambiguity,it needs to be solved by combining the pseudo-distance observation values of the measurement code.The relative positioning of carrier phase usually adopts the phase observation value to evaluate the difference.There are three common methods to evaluate the difference,namely,single difference method,double difference method and three difference method.The single difference method can eliminate the influence of satellite clock error and ephemeris error,the double difference method can not only eliminate the satellite clock error and ephemeris error,but also can eliminate the influence of receiver clock error,and the three-difference method can eliminate the influence of cycle slip.Therefore,when GNSS technology is applied to landslide deformation monitoring and prediction,double difference method of carrier phase relative positioning is needed to solve the problem.For the deformation monitoring of a landslide in the east of Lanzhou,the observation data of IGS base stations BJFS,LHAZ,TWTF and CUSV for 24 hours a day were put together with the observation data of three base points GP02,BX03 and JZ02 for the baseline calculation in the absence of high-precision reference points nearby.GAMIT/GLOBK software was used to calculate the coordinates of the three reference points,and the results were compared with those of TBC software.GAMIT software had advantages that could not be replaced by other commercial software in the process of long baseline and baseline calculation.In order to verify the feasibility of GNSS technology in landslide stability monitoring,8 Leica GS18 GNSS receivers are adopted to be installed on the base points and monitoring points of landslide deformation monitoring,among which 3 are installed on the base points,5 on the monitoring points,and 5 on the areas where landslide deformation is relatively obvious.Infinity software was used to solve the baseline calculation of the observed data,and the results were analyzed to obtain the baseline calculation accuracy of the landslide monitoring network.The maximum plane accuracy was 0.39 mm,the maximum elevation accuracy was 0.24 mm,and the maximum plane + elevation accuracy was0.46 mm.At the same time,TBC software was used for comparative calculation,and the adjustment error of geodetic coordinate elevation in the free network adjustment results was within 1mm.The plane grid coordinate east and north errors are 0,and the elevation errors are all within 1mm.In order to verify the feasibility of GNSS landslide deformation monitoring network in the aspect of elevation change(settlement observation),the monitoring network uses second-class leveling technology to conduct leveling of 8 monitoring sites while conducting GNSS static layout.The maximum difference in elevation between the leveling monitoring network and GNSS monitoring network is 5mm at BM11.By comparing the height increment of GNSS network baseline calculation and second-class leveling measurement on each baseline,the maximum value of baseline BM11-BM09 is 9mm.From the above results,GNSS deformation monitoring network can be applied to the settlement observation of deformation at cm level.(2)Appropriate reference points and reference networks should be selected.Monitoring points and points are of great importance for landslide deformation monitoring.Based on relevant examples,this paper analyzes the terrain,geology,scale of landslide and denature-characteristic of landslide,and analyzes the applicable conditions of different landslide monitoring network,so as to select an appropriate monitoring network for this landslide monitoring.The size,geological conditions,topographic conditions,development mechanism,deformation and equipment of a collapsible loess landslide in east Lanzhou are considered.In order to verify the stability of the relative position of the three reference points,three reference points are set in the deformation body and can be monitored by traditional instruments.A total of 8 monitoring points were set up,and the trailing edge of the slide-tension type landslide was the key observation area.Therefore,3 monitoring points and2 monitoring points were set up on both sides of the landslide body.At the same time,considering that the landslide has a transmission effect,1 monitoring point is set in the middle of the landslide and 2 monitoring points are set in the front end.(3)Trimble 4D landslide automatic prediction system consists of three parts: data processing center,real-time surface displacement monitoring,and Ethernet real-time data transmission.The data processing center equipped with Trimble 4D Control Monitoring software includes software installation and debugging,GNSS software configuration,total station software configuration,Ethernet configuration,Excle automatic download database data,etc.By collating and analyzing the monitoring data of GNSS receiver and total station,the deformation trend of landslide is predicted.Trimble Net R9 GNSS receiver and Trimble S9 total station are used to monitor the surface displacement and deformation of landslide in real time,and the 3d surface deformation information of landslide monitoring point can be collected in real time.Ethernet real-time monitoring data transmission ensures the stability of data transmission and provides communication guarantee for automatic monitoring and prediction of landslide.In order to realize automatic deformation monitoring and prediction of landslide,it is necessary to establish corresponding automatic monitoring indexes of landslide.The automatic monitoring indexes established according to the actual measured deformation data are more feasible and representative.A comparative analysis of the deformation amount and deformation rate on the top and both sides of a collapsible loess landslide in east lanzhou on June 30,2019 solstice and August 30,2020 for a total of 427 days.The average of the top three landslide monitoring deformation rate of 0.20 mm/d,on both sides of the ridge line monthly average deformation rate of 0.14 mm/d,front three monitoring average deformation rate is 0.21 mm/d,based on the index to determine the level of landslide deformation rate,it is concluded that the landslide deformation is safe,forecast for level 1 grade,deformation of slow and stable.