Journal of Hydroelectric Engineering

水力发电学报

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2023 Vol. 42, No. 7 Published: 2023-07-25

	1	Study on improved stiffness index and comprehensive evaluation of RCC dam material compaction quality ^Hot!
		LIU Donghai, YANG Gang, SUN Longfei
		DOI: 10.11660/slfdxb.20230701
		Effective control of the compaction quality of roller compacted concrete (RCC) is an important prerequisite for ensuring the safety and stable operation of dams. This paper formulates an improved stiffness index of RCC dam material, considering its lag phase angle, and presents a new method for measuring the lag phase angle. Then, we develop a comprehensive evaluation method of RCC compaction quality, using an XGBoost algorithm that couples this index, dam material properties, rolling parameters, and frequency domain compaction indexes. The results of case analysis show that the improved stiffness index can better characterize the compaction quality of dam materials. The comprehensive evaluation model has a relatively high accuracy, with a correlation coefficient of determination of 0.86 and an average relative error of 0.47% in compactness calculation against measurements, thus providing a new effective approach to the compaction quality control of RCC dam construction.
		2023 Vol. 42 (7): 1-11 [Abstract] ( 114 ) PDF (3145 KB) ( 343 )

	12	Study on water exchange between concentrated leakage passage and its surrounding media in dams
		XU Zengguang, LI Haiyang, CHAI Junrui, CAO Cheng, CHEN Donglai
		DOI: 10.11660/slfdxb.20230702
		When a concentrated leakage passage exists in the body of a dam, the passage will exchange water with its surrounding porous media driven by pressure difference. Such exchange may lead to an increase in dam discharge, but it is often ignored in traditional seepage field analysis. This study develops a sand tank model to simulate the presence of concentrated seepage channels in a dam, and examines the mechanism of water exchange and the water discharges from the concentrated leakage passage and the porous medium. A new formula for calculating the water exchange coefficient is then suggested. Results show that the amount of water exchange is proportional to passage diameter (D), porous medium permeability coefficient (Km), and hydraulic gradient (J). Orthogonal tests are adopted to analyze the influence degree of each factor on the water exchange capacity, revealing D is most influential, followed by J and Km. The results demonstrate the importance of the channel-medium exchange in seepage calculation, and would lay a basis for seepage field analysis of concentrated seepage channels in the dam.
		2023 Vol. 42 (7): 12-23 [Abstract] ( 82 ) PDF (4511 KB) ( 239 )

	24	Study on polymer-fracturing grouting simulations using extended finite element method and modified Cam-clay model
		LI Xiaolong, CHEN Kunyang, CHEN Can , LI Yuanyuan, ZHONG Yanhui, ZHANG Bei, WANG Fuming
		DOI: 10.11660/slfdxb.20230703
		Previous simulation methods of the splitting diffusion of self-expanding polymer materials in soils are not complete yet. This paper develops a new, preliminary simulation method for simulating the splitting compaction effect of polymer on soil. This method uses the extended finite element method (XFEM) to solve numerically the regional soil medium, and adopts a modified Cam-clay model to describe the mechanical characteristics of the soil. And it calculates slurry expansion pressure acting on the surfaces of a soil fracture iteratively using the relationship of polymer density versus confining pressure. We realize numerical solutions of the process of crack propagation in the soil, and verify them against experimental data. Example analysis shows that the method is applicable and effective in the simulation of the soil’s crack initiation process, propagation direction, and grout vein thickness variation under the expansive force, and it gives the distribution characteristics of deformation modulus, void ratio, stress field, and density field over the soil zone around a crack, thus laying a basis for further study of the splitting compaction mechanism of expansive polymer grouting material in soil.
		2023 Vol. 42 (7): 24-36 [Abstract] ( 64 ) PDF (885 KB) ( 337 )

	37	Study on effect of prior loading history on volumetric creep of rockfill materials
		SU Yu, WANG Fuqiang, DENG Gang, ZHANG Yinqi, ZHANG Yanyi, WANG Xiangnan
		DOI: 10.11660/slfdxb.20230704
		To investigate the volumetric creep characteristic of rockfill in depth, we conduct a series of confined creep tests on air-dried slate rockfill materials, using different prior loading stress rates and different pre-consolidation states. We find that the subsequent initial stage creep rate is positively correlated with the prior stress rate, but it is less affected by the latter if the prior stress rate is higher than a certain value. In normal consolidation state, if a higher prior loading rate is adopted, the time developing process of the subsequent creep rate conforms to the Singh-Mitchell model. If the prior loading rate is low, the creep rate in the initial stage is less than that at a faster prior loading, and then decreases slowly. This slow decrease continues for a certain time period until the creep rate varies with time in the same trend as the case of high prior loading rate－a negative linear relationship that exists between creep rate and time in double logarithmic coordinates. In over-consolidation state caused by prior loading or compaction, the subsequent initial stage creep rate and the total amount of creep deformation are still positively correlated with the creep stress and the prior loading stress rate, but their values are far smaller than those in the normal consolidation of the same creep stress and prior loading stress rate. Similar to the situation with lower prior loading stress rate in normal consolidation, the initial subsequent creep rate with a high prior loading stress rate in over-consolidation decreases slowly for a certain period, until the creep rate starts to decrease in the same way as the high prior stress rate case in normal consolidation. For the subsequent creep in over-consolidation with the same pre-consolidation stress, the higher the creep stress, the lager the subsequent creep deformation and the subsequent creep rate.
		2023 Vol. 42 (7): 37-45 [Abstract] ( 66 ) PDF (2502 KB) ( 137 )

	46	Study on dynamic mechanical properties of hydraulic asphalt concrete under compression-shear action
		DONG Jing, CHEN Liangliang, LIU Yunhe, YU Chengyang, QI Yujun
		DOI: 10.11660/slfdxb.20230705
		Study on the dynamic mechanical properties of hydraulic asphalt concrete under compression-shear load is important to ensure the safe operation of asphalt concrete core wall earth-rock dams. In this paper, we use an independently-developed compression-shear test device to study the dynamic mechanical properties of hydraulic asphalt concrete at different shear rates (0.0005 s-1, 0.001 s-1, 0.005 s-1 and 0.01 s-1) under different temperatures (5 °C and 15 °C) and different normal stresses (1 MPa, 2 MPa and 3 MPa). The results show that each specimen has obvious characteristics of oblique shear failure, and different normal stresses or shear rates impose an impact on its failure mode and shear stress-strain curve to different degrees. With increasing the normal stress or shear rate, shear strength and shear modulus increase; peak strain increases with the decreasing normal stress or increasing shear rate. Using the Mohr-Coulomb criterion, we obtain the laws of two strength parameters－cohesion c and internal friction angle φ of hydraulic asphalt concrete－varying with shear rate.
		2023 Vol. 42 (7): 46-55 [Abstract] ( 73 ) PDF (5017 KB) ( 211 )

	56	Dam deformation analysis model based on characteristic decomposition screening of coupling time series
		QI Yining, SU Huaizhi, YAO Kefu, YANG Jiaquan, XU Weinan
		DOI: 10.11660/slfdxb.20230706
		Accurate deformation prediction is of great significance to safe operation and long-term maintenance of dams, but previous methods have low prediction accuracy and lack sufficient information extraction from monitoring data. This paper constructs a relationship of dam deformation components versus their influencing factors through variational mode decomposition on the deformation series, and constructs Long Short-Term Memory neural networks with different structural parameters. Then, we develop a dam deformation analysis model that can realize optimal modeling through integrating the Grey Wolf Optimizer algorithm, the Minimum Redundancy Maximum Relevance method, and other strategies to improve its accuracy from three aspects－front-end decomposition, information extraction, and time series prediction. A case study shows that compared with the conventional monitoring model, this new model is more accurate in the simulations of dam deformation time variations and better in generalization performance, thus useful for dam deformation safety analysis.
		2023 Vol. 42 (7): 56-68 [Abstract] ( 94 ) PDF (777 KB) ( 350 )

	69	Improved zonal deformation prediction model for super-high arch dams
		HU Jiang, WANG Chunhong, LI Xing
		DOI: 10.11660/slfdxb.20230707
		Previous zonal deformation prediction models lack the capability of capturing spatial differences in the trend, periodic and fluctuating components of dam deformation. This paper describes an improved zonal deformation prediction model to solve this problem. First, we adopt a variational mode decomposition algorithm to split dam displacements into trend, periodic and fluctuating components, and determine the representative environmental and load factors using hierarchical clustering of the principal components, so that these factors can be decomposed into the trend, low- and high-frequency components according to their physical meanings. Then, an optimized dynamic time warping algorithm based on a shape-based distance is used to divide the displacement components at the measured points into different deformation zones; for these zones, a sequence of their centroids is calculated to capture shared characteristics. The zonal data sets of the centroid sequences and their strongly related components of the dominant influencing factors can be established. Finally, we construct an improved zonal deformation prediction models using three machine learning algorithms－random forest, least squares support vector machine, and boosted regression tree－and an improved hydrostatic-thermal-time model. These improved models are verified against the measurements of Xiluodu super-high arch dam. The verification shows satisfactory results in accuracy and well explains the spatiotemporal correlation and differences in the trend, periodic and fluctuating components of dam displacements.
		2023 Vol. 42 (7): 69-83 [Abstract] ( 69 ) PDF (1119 KB) ( 326 )

	84	Risk evaluation of urban flooding with social information
		WANG Qianning, ZHOU Zhiyi, WU Jian, LIU Fuxin, WANG Xinyi, PENG Yong, ZHANG Chi
		DOI: 10.11660/slfdxb.20230708
		This paper presents a novel method for urban flooding risk assessment, incorporating social information that was not yet or less considered in previous studies. We have obtained flooding data from an urban storm water model and collected social information from webpages using the web crawler technology. Then, using these two types of information, we build an assessment index system of urban flooding and an exponential model, so as to achieve a comprehensive evaluation of urban flooding risk for the study area. Application to a study site, the Qingnishier region in Dalian, shows that for the 50- and 100-year return periods, the calculated areas of high-risk zones are 0.53 km2 and 1.24 km2, respectively, if only the flooding information is taken into account, while they become 1.12 km2 and 1.50 km2, respectively, if the social information is also included, revealing considerable increases in the latter case. Incorporating social information in the model will significantly raise the flooding risk level in strategic locations such as densely populated urban areas, traffic arteries, but it will lower the risk level in those unimportant areas, which indicates an improvement of the modeling.
		2023 Vol. 42 (7): 84-95 [Abstract] ( 86 ) PDF (8545 KB) ( 142 )

	96	Study on optimizing drought-resistant strategy of staged reservoir operation based on Bayes decision
		LI Jie, LIU Zhao, MAO Qinnan, YU Yucong, YANG Zhou, WANG Shumin
		DOI: 10.11660/slfdxb.20230709
		Under the influence of global climate change and ever-increasing human activities, frequent droughts have imposed great impacts on social and economic developments. The study on drought-resistant strategies for staged reservoir operation can produce a remarkable effect on efficient utilization of water resources, drought-resistance, and disaster reduction. This paper examines how to determine an optimal drought-resistant scheduling strategy in multi-year available water supply combination scenarios based on the minimum risk Bayesian decision, using a bee colony algorithm and a reverse recursion method that is equipped with an objective function to maximize water supply guarantee rate and minimize water supply failure depth. In a case study of the Jinpen reservoir in the Heihe River basin, we make a comparative analysis of the drought-resistant strategy of its operation based on the Bayes joint reverse sequential recursion, against those based on conventional operation, traditional reverse sequential recursion, and optimized reverse sequential recursion. We find that the former can not only reduce the probability of extreme water shortage under extreme drought conditions, but also improve the water supply guarantee rate and reduce the water supply failure depth. This shows the Bayes decision-based operation strategy raises the capability of a reservoir against extreme droughts and lays a theoretical basis for drought-resistant operation.
		2023 Vol. 42 (7): 96-107 [Abstract] ( 81 ) PDF (2889 KB) ( 226 )

	108	Identifying upstream-downstream relationship of cascade reservoirs in Xijiang River watershed
		DING Qirong, ZHAO Tongtiegang, TIAN Yu, YAN Denghua, CHEN Xiaohong
		DOI: 10.11660/slfdxb.20230710
		Upstream-downstream relationship among cascade reservoirs is a key component of water resources system modelling. This paper builds a framework for identifying this relationship based on the river coding method, and applies it to analysis of the spatial characteristics of a cascade reservoirs system and its watershed development and utilization. In a case study of the Xijiang River watershed, the results show the cascade reservoirs are connected only by a few of them, and more than 70% are functionally headwater reservoirs. Only five of them are leading reservoirs that have the largest confluence areas and totally control 23.6% of the watershed area, but they play a key role in flood control, water supply, and power generation through their hydraulic connections with many upstream reservoirs. Overall, each tributary in this watershed presents obvious characteristics of typical cascade development, and the number of its upstream reservoirs increases exponentially with the raising in its grade. The results are of great significance for analyzing the function of cascade reservoirs.
		2023 Vol. 42 (7): 108-118 [Abstract] ( 93 ) PDF (5322 KB) ( 181 )

	119	Numerical study of optimizing on-cam operation of horizontal bulb tubular turbines
		ZHAO Yaping, QIN Dige, ZHENG Xiaobo, LI Zhihua, LIAO Weili
		DOI: 10.11660/slfdxb.20230711
		Differences exist between the prototype machine at a tubular power station and its model machine, often leading to an incorrect on-cam operation relationship of the guide vanes and runner blades. This could cause many power stations after being put into operation to suffer from insufficient output and severe vibration. However, adjusting the on-cam operation through on-site prototype experiments is time-consuming and labor-intensive. In this work, numerical optimization of the on-cam operation of a prototype tubular turbine is studied using the dynamic grid technology, considering the effect of free surface and water gravity. The results show that before and after the optimization in low head conditions, the turbine has a wider range of variations in on-cam operation, and its efficiency is more sensitive to changes in guide vane opening. Therefore, for a hydropower station under low head conditions during the wet season, an on-cam operation adjustment is more necessary, and numerical simulations of the optimization is of greater significance. An adjustment to on-cam operation usually imposes a significant impact on the flow regime in the runner near the hub, and a good one will cause an increase in the relative flow angle and a decrease in the positive circular rector at the outlet of the runner near the hub. This brings about a significant improvement in the distribution of backflows and vortex belts in the draft tube, thereby reducing hydraulic loss in the draft tube and raising hydraulic efficiency of the tubular turbine. Thus, numerical optimization of on-cam operation is a useful guide for the design and field test of tubular units.
		2023 Vol. 42 (7): 119-128 [Abstract] ( 64 ) PDF (1776 KB) ( 223 )