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Monitoring models for base flow effect and daily variation of dam seepage elements considering time lag effect

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Water Science and Engineering 2018年第4期11卷 344-354页

作者： Shao-wei Wang Ying-li Xu Chong-shi Gu Teng-fei Bao School of Environmental and Safety Engineering Changzhou University State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University

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 *** 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.

关键词： Dam seepage monitoring model time lag effect Support vector machine(SVM) Sensitivity analysis Base flow Daily variation Piezometric tube water level

effects of time lag and stress loading rate on permeability in low permeability reservoirs

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Mining Science and Technology 2009年第4期19卷 526-530页

作者： WANG Rui YUE Xiang-an ZHANG Wei TAN Xi-qun ZHANG Yan MOE Key Laboratory for Petroleum Engineering China University of Petroleum Beijing 102249 China Sinopec Exploration ＆ Production Research Institute Beijing 100083 China China Huayou Group Corporation Beijing 100011 China

In order to study the effect of time lag and stress loading rates on rock deformation,the conventional stepped stress loading mode was changed into a continuous mode to investigate the effect of effective pressure on permeability and *** time lag effect of rock deformation illustrating the relationship between changes in permeability and steady time was *** reduction ratios were measured under different stress loading rates which were achieved by different pump rate *** results show that permeability and porosity gradually decrease with increases in effective *** at high effective pressure attains stability *** times at low effective pressure are very *** in permeability at lower stress loading rates is small,while,in contrast,it is large at high stress loading rates.

关键词： low permeability stress sensitivity time lag effect stress loading rate

Model-scale tests to examine water pressures acting on potentially buoyant underground structures in clay strata

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第3期14卷 861-872页

作者： Zhisheng Ren Qixian Lu Kaiwen Liu Pengpeng Ni Guoxiong Mei School of Civil Engineering Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)Guangdong Key Laboratory of Oceanic Civil EngineeringGuangdong Research Center for Underground Space Exploitation TechnologySun Yat-sen UniversityGuangzhou510275China Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education College of Civil Engineering and ArchitectureGuangxi UniversityNanning530004China State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan430072China Key Laboratory of High-speed Railway Engineering(MOE) School of Civil EngineeringSouthwest Jiaotong UniversityChengdu610031China

Throughout the service life, underground structures are subjected to transient and sustained hydrostatic pressures. The reservoir impoundment results in an increase in water level, as well as hydraulic gradient,which can endanger the uplift performance of infrastructure. In uplift design, a reduction factor is often suggested for buoyant force acting on underground structures in clays due to the time lag ***, the mechanism of pore pressure generation in clays is not fully understood. This investigation presents a novel U-shaped test chamber to assess the pore pressure generation with time in the horizontal branch subjected to an increase in reservoir level in the left vertical branch. A mathematical model is developed to explain the time lag effect of pore pressure generation. The test program also involves the evaluation of uplift pressure acting on foundation model in the right vertical branch due to adjacent reservoir impoundment. It is found that the time lag effect of pore pressure generation in clays can be observed irrespective of hydraulic gradient, but a higher hydraulic gradient can lead to a faster response in pore pressure sensors. A reduction factor of 0.84-0.87 should be considered to reduce the conservatism of uplift design.

关键词： Buoyant force Reservoir impoundment Pore pressure generation Reduction factor Uplift pressure time lag effect

Grassland coverage inter-annual variation and its coupling relation with hydrothermal factors in China during 1982-2010

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Journal of Geographical Sciences 2014年第4期24卷 593-611页

作者： ZHOU Wei GANG Chengcheng CHEN Yizhao MU Shaojie SUN Zhengguo LI Jianlong School of Life Science Nanjing University Nanjing 210093 China College of Animal Sciences Nanjing Agricultural University Nanjing 210095 China

GIMMS （Global Inventory Modeling and Mapping Studies） NDVI （Normalised Difference Vegetation Index） from 1982 to 2006 and MODIS （Moderate Resolution Imaging Spectroradiometer） NDVI from 2001 to 2010 were blended to extract the, grass coverage and analyze its spatial pattern. The response of grass coverage to climatic variations at annual and monthly time scales was analyzed. Grass coverage distribution had increased from northwest to southeast across China. During 1982-2010, the mean nationwide grass coverage was 34% but exhibited apparent spatial heterogeneity, being the highest （61.4%） in slope grasslands and the lowest （17.1%） in desert grasslands. There was a slight increase of the grass coverage with a rate of 0.17% per year. Increase in slope grasslands coverage was as high as 0.27% per year, while in the plain grasslands and meadows the grass coverage in- crease was the lowest （being 0.11% per year and 0.1% per year, respectively）. Across China, the grass coverage with extremely significant increase （P〈0.01） and significant increase （P〈0.05） accounted for 46.03% and 11% of the total grassland area, respectively, while those with extremely significant and significant decrease accounted for only 4.1% and 3.24%, respectively. At the annual time scale, there are no significant correlations between grass coverage and annual mean temperature and precipitation. However, the grass coverage was somewhat affected by temperature in alpine and sub-alpine grassland, alpine and sub-alpine meadow, slope grassland and meadow, while grass coverage in desert grassland and plain grassland was more affected by precipitation. At the monthly time-scale, there are significant correlations between grass coverage with both temperature and precipitation, indicating that the grass coverage is more affected by seasonal fluctuations of hydrothermal conditions. Additionally, there is one-month time lag-effect between grass coverage and climate factors for each grassland types.

关键词： grass coverage climate factors spatial-temporal dynamic correlation time lag effect

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