Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend an...Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.展开更多
A zoned embankment dam is founded on clay underlain by a sand deposit.Major seepage phenomena were noticed in the foundation downstream from the dam where the vertical seepage forces in the sand layer were expected to...A zoned embankment dam is founded on clay underlain by a sand deposit.Major seepage phenomena were noticed in the foundation downstream from the dam where the vertical seepage forces in the sand layer were expected to exceed the downward forces due to the overlying clay.Modern technologies were applied to delineate critical zones to help design optimal rehabilitation measures.A global electromagnetic survey was carried out to detect and map the main sources,pathways and exits of seepage.Based on these global findings,a more detailed analysis was then conducted to identify zones where thickness of the foundation clay is minimal,pore pressures in sand are higher and thus where the factor of safety against uplift is lower and internal erosion is more likely to occur.Clay thickness evaluation required the determination of land surface as well as clay-sand contact elevations.A laser airborne survey was performed to model the land surface elevation.Data concerning the clay-sand contact elevation came from the interpreted stratigraphy based on a series of boreholes and cone penetration tests.This data was combined in a geostatistical model along with the measured piezometric levels in the foundation.This resulted in a contour map showing factors of safety against uplift over the entire downstream area.The use of modern technologies,namely electromagnetic and laser surveys as well as geostatistical tools,was instrumental in defining the limits of an otherwise spread-out problem and to provide an optimal solution,in terms of costs and effectiveness,for the long-term stabilization of the foundation.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51709021)the Open Foundation of the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering(Grant No.2016491111)
文摘Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.
文摘A zoned embankment dam is founded on clay underlain by a sand deposit.Major seepage phenomena were noticed in the foundation downstream from the dam where the vertical seepage forces in the sand layer were expected to exceed the downward forces due to the overlying clay.Modern technologies were applied to delineate critical zones to help design optimal rehabilitation measures.A global electromagnetic survey was carried out to detect and map the main sources,pathways and exits of seepage.Based on these global findings,a more detailed analysis was then conducted to identify zones where thickness of the foundation clay is minimal,pore pressures in sand are higher and thus where the factor of safety against uplift is lower and internal erosion is more likely to occur.Clay thickness evaluation required the determination of land surface as well as clay-sand contact elevations.A laser airborne survey was performed to model the land surface elevation.Data concerning the clay-sand contact elevation came from the interpreted stratigraphy based on a series of boreholes and cone penetration tests.This data was combined in a geostatistical model along with the measured piezometric levels in the foundation.This resulted in a contour map showing factors of safety against uplift over the entire downstream area.The use of modern technologies,namely electromagnetic and laser surveys as well as geostatistical tools,was instrumental in defining the limits of an otherwise spread-out problem and to provide an optimal solution,in terms of costs and effectiveness,for the long-term stabilization of the foundation.
