Earth-rockfill Dam Surface Deformation Analysis And Modeling Based On BDS/GPS Times Series Results

As a result of the dead load,hydraulic load and earthquakes,dam deformation remains along its full life cycle.Deformation monitoring and results analysis on the dam surface help to understand the dam operation states,grasp its deformation pattern and furtherly forecast and early warn.In China,there are nearly 100,000 reservoirs with a water storage capacity over 100,000 m3,and most of them are allocated with small or medium size earth-rockfill dam.For a long time,a manual method using"total-station and levelling" is mostly applied to dam deformation monitoring,which is neither real-time nor continuous.With the application of GPS,this problem can be perfectly solved.Therefore,GPS technology is widely adopted in big dams which belong to well-known water conservancy projects like Geheyan reservoir,Xiaolangdi reservoir and Nuozhadu hydropower station.As we know,signal blocks due to slopes and surroundings of these projects could lead to a shortage in visible satellites,bad satellites geometry structure,and even drop in precision,if stand-alone GPS were applied.Thus,it is necessary to position with multi GNSS system observations.By the end of 2012,BDS(Beidou Satellite System)is capable to provide regional positioning service.In this paper,application of BDS/GPS in automated dam deformation monitoring is studied.Taking Xikeng reservoir BDS/GPS automated dam deformation monitoring system as an example,its prototype design and realization were discussed firstly,then data quality and precision were assessed,and lastly,dam displacements time series with a time span of 2 years were analyzed to achieve deforming characteristics and patterns of this dam.Model for displacements time series in Y direction was fitted and compared utilizing times series analysis,multiple regression analysis and load regression model proposed in this paper.The main work and contribution are concluded as follows:1.Fundamental theory of BDS/GPS combined relative positioning was summarized from aspects like datum unification,observation equation,double difference observation equation and influence and elimination of observation errors.2.Fundamental theory(including mathematical statistics model,deterministic model and mixed model)for dam deformation modeling was introduced and compared,and simplified modeling process of commonly used modeling methodology for small and medium size earth-rockfill dams was given.3.Taking Xikeng reservoir BDS/GPS automated dam deformation monitoring system as an example,we discussed its prototype design and realization.Its precision and reliability were then validated by statistical and experimental analysis,showing that baseline resolution was under 2mm in both X and Y and 3mm vertically for 4h session and under 2mm in X,1mm in Y and 2.5mm in Z for 24h session.The precision of BDS/GPS fusion is 10.3%better than that of GPS horizontally.4.With BDS/GPS observation data from monitoring stations in 3#transverse section,data quality was analyzed and compared to each other.The result showed that data quality of monitoring stations near to the bottom were worse than those on both side of the top.5.By characteristic analyzing for dam displacements time series with 2 years' time span,we proposed a hydraulic load regression model combining dam structure and water level data and compared both fitting and forecasting effect of this model with time series model and multiple regression model.It showed that,this model could well meet the pattern and scale of dam displacements,and explain the physical process of dam displacements in Y.It is capable for similar earth rock-fill dam deformation analysis and modeling.