水力发电学报
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2021 Vol. 40, No. 2
Published: 2021-02-25
 
     
1 Low-water channel adjustment in middle Yangtze River after operation of Three Gorges Project and its effect on navigation Hot!
XIA Junqiang, LIU Xin, YAO Jizhuo, ZHOU Meirong, DENG Shanshan
DOI: 10.11660/slfdxb.20210201
Since the operation of Three Gorges Project (TGP), significant channel erosion has occurred in the middle Yangtze River (MYR) mainstream, resulting in continual adjustments in low-water channel morphology in its different sub-reaches. This paper determines the low-water channel dimensions for different cross-sections of this reach, and calculates the reach-scale low-water channel dimensions for its four sub-reaches of 2003 to 2016 using a reach-averaged method. We find that the channel was developing into a narrower and deeper geometry and its width-depth ratio was generally decreased, thereby resulting in an improvement on navigation conditions. In addition, we develop empirical relationships of the low-water channel dimensions versus the previous years’ flow and sediment regime for different sub-reaches. The relationships show that in this period, the determination coefficients were maximized in the Yizhi and Jingjiang reaches at a flow-sediment responding lag of five years, while maximized in the Chenghan and Hanhu reaches at the lag of seven years. In all these sub-reaches, the adjustments of low-water channel morphology were significantly affected by the incoming flow and sediment conditions in the previous five or seven years respectively. Overall, the low-water channel (except for the width) responded well to the altered flow-sediment regime, and its adjustment will be larger in the sub-reaches closer to the dam.
2021 Vol. 40 (2): 1-11 [Abstract] ( 210 ) PDF (920 KB)  ( 654 )
12 Assessment method of benefits of interconnected water systems in data-scarce regions
ZHU Shijie, MAO Jingqiao, DAI Huichao
DOI: 10.11660/slfdxb.20210202
A great difficulty lies in applying the traditional index system to assessing water system connectivity in data-scarce regions, a Gordian knot in the management of ecological water conservancy projects. Based on the easy-to-access satellite data and conventional water quality data, we extract three characteristic indexes – water system connectivity, landscape fragility, and water quality pollution, and establish a comprehensive benefit index (CEI) for the projects of interconnected water systems (PIWS) in data-scarce regions. Then, the Delphi method is used to determine the weight, and fuzzy comprehensive evaluation is used to evaluate quantitatively the PIWS in the Gongqingcheng City in 2018 and 2019. The results show that its CEIs of these two years were 2.014 and 1.906 respectively, while its water system connectivity or landscape fragility index did not change significantly and water quality pollution index was the main pressure factor. The CEI-based method can not just assess quantitatively the PIWS effect in the absence of statistical data, but offer a spatiotemporal analysis of the indicators, helping improve the construction of similar projects.
2021 Vol. 40 (2): 12-19 [Abstract] ( 141 ) PDF (4430 KB)  ( 734 )
20 New approach to flume experiment for transport capacity of fine suspended sediment
YUAN Qiang, ZHANG Man, ZHOU Jianjun
DOI: 10.11660/slfdxb.20210203
River sediment transport capacity is of a key issue in suspended sediment studies. Due to the strong time-lag of fine sediment adjustment, it is difficult to obtain an equilibrium condition by the traditional recirculating flume experiments, especially for fine graded sediment. In this study, a special sand feeder and an outlet filter were implemented to the traditional experimental flume system, and experiments were carried out to approach the equilibrium transport process through sedimentation. Results were compared with traditional experiment data and the existing transport formulas, indicating: i) the implemented system can load more accurate inlet sediment for given compositions with the proposed feeder and outlet filter; ii) the non-equilibrium experiment can rather better approach equilibrium transport in a flume reach over the self-established depositional delta, where a sediment concentration, that is slighly higher than the actual transport capacity, can easily obtained without measurements; iii) results of limited runs indicate an extensively lower transport capacity than that from traditional experiments. Preliminary results reveal a somehow overestimation by the traditional formulas that calibrated using previous experiment data.
2021 Vol. 40 (2): 20-30 [Abstract] ( 171 ) PDF (3044 KB)  ( 619 )
31 Effect of water level fluctuation in flood season on thermal stratification and water quality in Xiangxi Bay
ZHAO Xingxing, JI Daobin, LONG Lianghong, HUANG Yanan, CHENG Zaiqiang
DOI: 10.11660/slfdxb.20210204
In this study, we have conducted field measurements in Xiangxi River, a typical tributary of the Three Gorges reservoir, to collect the meteorological and hydrological data of daily variations for the period of June 5 to 30 August, 2019, including water temperature and water quality measurements. This paper focuses on an analysis of the effects of water level fluctuation in Xiangxi Bay on its thermal stratification and water quality in flood season. The results show the daily cycle of an upper warm layer that led to sub-daily variations in the mixed layer depth in a range of 0.0 - 19.4 m, but in long term this depth was significantly negatively correlated with water level fluctuations (P = - 0.47). The bottom water temperature increased slowly and this increase was impacted by the cold inflows at the bay inlets significantly. No stable thermocline was observed due to strong mixing driven by the intrusion of density currents and vertical convection. Significant correlations of dissolved oxygen content and saturation degree with Chl.a concentration indicate the variations in dissolved oxygen can be caused by phytoplankton distribution. Further analysis reveals that large water level fluctuation could vary the plunge depth of density currents, and a shift from the overflow to interflow mode of the currents will result in altered mixing regime in the tributary bay, i.e., reducing the surface mixed layer and increasing vertical stratification, both significantly different from those of the reservoir filling period. This study sheds light on new understanding for effective utilization of water level fluctuation (through reservoir regulation) to improve water quality in the tributaries of Three Gorges Reservoir.
2021 Vol. 40 (2): 31-41 [Abstract] ( 175 ) PDF (4459 KB)  ( 613 )
42 Multi-objective optimal operation of cascade reservoirs in Xijiang River Basin considering different saltwater-suppressing levels
BAI Tao, LIU Xia, ZHANG Ming, HUANG Qiang
DOI: 10.11660/slfdxb.20210205
Salt tide intrusion has always been an important factor of water supply safety in the Xijiang River Basin, and reasonable reservoir operation becomes a key measure to suppress saltwater and fill freshwater. This study develops a real-time optimal operation model for the cascade reservoirs in the Xijiang River basin to maximize both the cascade’s total power output and the lower limit of saltwater-suppressing flows, considering power generation benefits and the saltwater-suppression goal for the downstream Wuzhou section. The results show that the basin should increase power output mainly by raising the Yantan reservoir’s water stage and the risk of salt suppression, while the other reservoirs be responsible for reducing this risk and ensuring the saltwater-suppression flowrate. With the basin inflow at a frequency of 90%, a loss of 0.06% in the cascade power output leads to the suppressing flow to be increased up to 3163 m3/s at Wuzhou in operation period. With a 95% basin inflow, the power output will be increased by 330,000 kW·h, while the saltwater suppression guarantee level increased to a period of three days. The results reveal how the saltwater control risk to transfer between different reservoirs, enhancing water supply safety for the Pearl River delta and the Greater Bay area.
2021 Vol. 40 (2): 42-52 [Abstract] ( 199 ) PDF (613 KB)  ( 468 )
53 Analysis on monthly trans-province transmission capacity of large-scale hydropower stations
CHENG Xiong, TANG Yingling, LIU Ji, ZHONG Hao, LI Wenwu, WU Yaliang
DOI: 10.11660/slfdxb.20210206
The trans-province transmission capacity of large-scale hydropower stations depends on the sending end factors: the installed scale, regulating performance, natural water flow, and ultra high-voltage power transmission capacity. This paper presents an analysis model of the trans-province transmission capacity of large-scale hydropower stations. This model evaluates the time variations in runoff in different months using a flood-dry season method, and uses a power maximization model to calculate the maximum theoretical power generation of the hydropower system under the inflows of different frequencies. Then, it analyzes the power balance of the grid. If the daily generating capacity, after the local and overseas load demands deducted, is higher than the total capacity of trans-province transmission, it indicates that the current transmission channel are not enough to meet the demand of external transmission, and new channels should be added to avoid water spilling. The model is applied to the trans-province transmission of the large-scale hydropower stations in Yunnan. The results indicate our model is effective and satisfactory in quantitative analysis of the transmission capacity under different inflow conditions, as a theoretically and practically useful tool for improving the absorption capacity of clean energy and the planning and construction of new transmission channels.
2021 Vol. 40 (2): 53-63 [Abstract] ( 140 ) PDF (899 KB)  ( 345 )
64 Optimization and decision-making model of multi-power grid joint operation for promoting clean energy consumption
JI Changming, ZHAO Yawei, ZHANG Yanke
DOI: 10.11660/slfdxb.20210207
In Southwest China, tremendous power has been abandoned and the consumption of clean energies hindered. Aimed at this problem and the minimum operation cost of interconnected power grids, this study develops a multi-objective optimization model of multi-power grid joint operation, considering clean energy consumption and power sending-out. This model uses the niche multi-objective particle swarm optimization (NMOPSO) algorithm to seek Pareto frontiers, and the entropy-based technique for order preference by similarity to ideal solution (TOPSIS) to decide the optimal trade-off solution. It is applied in a case study of one sending grid plus two receiving grids system for power transmission from Yunnan to Guangdong and Guangxi. The results show that NMOPSO gives approximate Pareto frontiers with a uniform distribution; the TOPSIS optimal trade-off solution is featured with a clean energy consumption rate up to 100% of that of the sending grid and daily hours of the transmission channels in use reaching the greatest. Thus, our new method of optimization calculation greatly improves the grids’ consumption capability of clean energy and the use factor of transmission channels.
2021 Vol. 40 (2): 64-76 [Abstract] ( 170 ) PDF (2676 KB)  ( 627 )
77 Study on design rainfalls in Beijing based on Copula functions
ZUO Binbin, XU Zongxue, YE Chenlei, REN Meifang, CHEN Hao
DOI: 10.11660/slfdxb.20210208
An accurate description of design rainfalls with different return periods is an important basis for planning and design of water conservancy structures, flood control, and disaster reduction. Based on the hourly rainfall data of 2005 to 2018 from 20 stations in Beijing, this study uses an over-threshold method to extract the depth and duration of heavy rainfalls over different regions, and estimates their joint distribution functions to calculate the design rainfalls of different return periods in each region. The results show that significantly more heavy rainfall events were observed in the downtown of this city than in the mountainous areas; the duration of most rainfalls follows the generalized extreme value (GEV) or Lognormal distributions, while the rainfall depths follow the GEV distribution. The joint distribution of the depth and duration of rainfalls is better characterized using a Gumbel Copula function for most of the regions in the study area, while a Frank Copula function is better in several other regions. The use of binary Copula functions can improve the estimation of design rainfalls of different return periods.
2021 Vol. 40 (2): 77-88 [Abstract] ( 180 ) PDF (1188 KB)  ( 499 )
89 Fitting reservoir stage-capacity curves and its application in reservoir operation
JIA Benjun, ZHOU Jianzhong, CHEN Xiao, TIAN Mengqi, ZHANG Yongchuan
DOI: 10.11660/slfdxb.20210209
Discrete representation of the stage-capacity curve of a reservoir in a power generation dispatching model usually leads to difficulty in mathematical analysis and low efficiency in model solution. However, this relationship lacks a unified function expression and we need to examine its curve fitting. Using discrete data points of reservoir stage and capacity measured in-situ, this study derives the relationship for three different curves through linear and nonlinear least square fitting, and evaluates comprehensively their goodness of fit and the effect in practical application. A case study of 23 reservoirs in the upper Yangtze basin shows that in describing the relationship, stage-capacity curves of the power function have wide applicability and good reliability and can be used as a general curve type. The study can help promote a unified analytical expression of reservoir stage-capacity relationship and improve the solution efficiency of hydropower generation scheduling and optimization models.
2021 Vol. 40 (2): 89-99 [Abstract] ( 211 ) PDF (3565 KB)  ( 612 )
100 Study on improved nonparametric disaggregation model of monthly runoff using variable kernel
WU Haohao, SONG Songbai
DOI: 10.11660/slfdxb.20210210
Synthetic simulation of streamflow series can afford a reliable basis for planning and management of a water resources system. Previous nonparametric disaggregation models cannot preserve a back and forth auto-correlation structure of variables and may lead to boundary problems of generating a large number of negative values of flow. In this paper, we apply the kernel density estimation theory to develop an improved nonparametric disaggregation model of monthly streamflow through a comprehensive consideration of the relationship among annual runoff, previous first-order monthly runoff, and simulated monthly streamflow, using the variable kernel bandwidth method to reduce boundary impact. This model is compared with the traditional relative disaggregation model, and used for simulating the natural monthly runoffs at Lanzhou station in the Yellow basin for the period of 1932 to 2010. The results show it can better preserve the probability distribution and statistical parameters of the original runoff series, overcome the inconsistency in the back and forth auto-correlation structure, and avoid generating negative flows, thus being applicable to stochastic simulations of monthly streamflow.
2021 Vol. 40 (2): 100-110 [Abstract] ( 121 ) PDF (1072 KB)  ( 412 )
111 Extraction of water body information from GF-1 satellite images using spatiotemporal reconstruction approach
BAI Liangliang, ZENG Chao, GE Changsong, HUANG Qi, LONG Di
DOI: 10.11660/slfdxb.20210211
To facilitate dynamic monitoring of the spatial distribution of water bodies in the Three Gorges reservoir area, we have developed a framework of water body detection, reconstruction and extraction using China’s GF-1 satellite images of high spatiotemporal resolution. Results show the method of object-oriented change detection has an overall accuracy of cloud detection up to 97%, with the producer's accuracy and user's accuracy of cloud detection both higher than 76%. Large cloud-contaminated areas can be effectively recovered using a spatiotemporal reconstruction approach, which can reflect the complete spatial variations. In addition, we find the water surface area of this reservoir, with a mean of 540.6 km2, did not significantly increase or decrease during 2013-2017. This study is useful for comprehensive, integrated management of the reservoir area, with important implications for applying GF-1 satellite images in this region.
2021 Vol. 40 (2): 111-120 [Abstract] ( 251 ) PDF (3118 KB)  ( 668 )
121 Derivation of river surface temperature from Landsat thermal infrared data
SHI Xi, SUN Jian, SHI Lidi
DOI: 10.11660/slfdxb.20210212
水温是影响河流环境与生态过程的重要因素。应用卫星遥感资料反演海洋和湖泊等大尺度水体温度的方法流程已较为成熟，但对于河流或河道型水库，受河道尺度、岸线边界及河道内船舶等随机因素影响，水温反演数据质量较差，目前还没有较完整的数据处理流程。本文基于Landsat系列卫星数据，应用大气辐射传输模型反演了三峡水库库首庙河站及库尾寸滩站两个特征站位的水体表面温度，并使用增强水体获取方法进行水体-陆地边缘效应的剔除，采用不同验证窗口选取方法确定的反演温度与实测水温进行比对验证。研究结果表明，剔除边缘异常像素可显著提高水温反演精度，误差可降低0.2℃以上；相较于单栅格法，利用方形选框法可使误差降低约0.1℃；本文所提出的水温反演方法在两个特征研究区域内具有相同的精度，并且Landsat-5的反演精度较Landsat-7更高，其均方根误差处于0.87 ~ 0.91℃。本文反演方法和数据处理过程可为今后使用Landsat系列卫星遥感影像获取河道内水温数据提供参考数据处理流程。
2021 Vol. 40 (2): 121-130 [Abstract] ( 412 ) PDF (2571 KB)  ( 583 )
131 Hydraulic performance analysis of reverse osmosis seawater desalination turbo energy recovery device
LIU Zishi, XIAO Yexiang, WANG Chengpeng, ZHU Yilin, LIU Sihan, CUI Yongkang, YIN Xilong
DOI: 10.11660/slfdxb.20210213
Nowadays, reverse osmosis (RO) seawater desalination has already become a type of the widest application of all the desalination technologies. A RO desalination device usually consumes much energy, since in working mode it needs to retain a RO membrane work pressure of about 6 MPa at the seawater side to produce fresh water continuously; and after RO processing, a large amount of pressure energy still remains in the concentrated brine. Therefore, adding a turbo energy recovery device – that takes advantage of the pressure energy left in the concentrated brine to drive the pump side and boosts feed-seawater pressure – can greatly reduce energy consumption. This study focuses on an analysis of such a device running in the RO seawater desalination plant on Sansha Island. First, we develop a numerical model for the 3D steady flows in the entire channel of both its pump side and turbine side, using a SST model to account for turbulence effect. Then, we simulate its channel flows under different operating conditions, and analyze the hydraulic performances and flow behaviors of its turbine and pump sides based on numerical simulations. The results show that the calculated overall energy conversion efficiencies of this device agree well with measurements; under the present optimal operating condition, the hydraulic efficiency of its turbine or pump side has a large room for improvement. The turbine side features with a relatively wider range of high-efficiency operation. Under partial operating conditions, both the turbine and pump sides show a reduction in hydraulic efficiency and more complicated internal flow patterns.
2021 Vol. 40 (2): 131-140 [Abstract] ( 232 ) PDF (3455 KB)  ( 473 )
141 Analysis of power oscillation of generating units at Bailianhe pumped-storage power station
XIA Ziping, YAN Wenjie, YANG Jiebin, CHENG Yongguang, HUANG Gaopeng, YANG Jiandong
DOI: 10.11660/slfdxb.20210214
This paper explores the cause of power oscillation and analyzes its relationship with system parameters through a case study of the power oscillation of generating units at Bailianhe pumped-storage station in generation mode under the conditions of low heads and large valve openings. First, we construct a one-dimensional numerical model for time domain analysis including the calculation of draft tube cavity vortices; then, the method of characteristics is used to solve the model with its simulations compared with measurements. Finally, we conduct a sensitivity analysis of the relationship between cavity vortex parameters, governor parameters, peak opening and closing speeds of guide vanes, regulation mode, and power oscillation. The results show that the power oscillation is caused by the cavity vortex rope, while governor parameters or peak opening and closing speeds have little effect on its occurrence under the influence of the cavity vortex. And it mainly depends on the cavity compliance and the mass flow gain factor of the cavity vortex rope. Thus, the results lay a theoretical basis for safe operation of pumped-storage stations.
2021 Vol. 40 (2): 141-148 [Abstract] ( 257 ) PDF (3077 KB)  ( 593 )
149 Study on influence of weak climbing vibration on plane gate vibration
LIU Fang, WU Minrui, LI Wensheng, SHENG Chuanming, XU Guobin
DOI: 10.11660/slfdxb.20210215
This study examines the phenomenon of weak climbing vibration during hydrodynamic gate closing and its effect on gate vibration through an experiment on a 1:25-scale hydroelastic plane gate model for the Batang hydropower station. We control the weak gate vibrations by changing the upstream water stage, observe time variations in local stress at different locations of the gate and in its overall acceleration and displacement during gate closing after weak climbing vibration starts, and examine the characteristics of gate vibrations. The results show that 1) weak climbing vibration does not modify the overall vibration modes of the gate, though it can increase the energy of vertical vibration acceleration by 2.6 times. 2) The gate’s vertical vibration displacement is about 11 times that of the non-climbing vibration case, with its mean square deviation amplitude beyond the standard, indicating a serious vibration that may produce adverse effects on the gate and its connection structures. 3) Weak climbing vibration has the greatest effect on the measuring point No.15 located directly below the lifting lug and could tear the lug under high water head conditions. A roughly 10-time increase in the dominant frequency of stress can be observed at this point, and the local forced vibration of the gate switches to the state of periodic vibration. Thus, to avoid structure damage, it is necessary to strengthen the upper part of the main longitudinal beam of the gate and the lifting lug, which are both greatly affected by climbing vibration.
2021 Vol. 40 (2): 149-157 [Abstract] ( 118 ) PDF (835 KB)  ( 396 )
158 Study on optimization of start-up modes of Francis hydropower units
WU Shuangjie, QI Jie, AN Xueli, PAN Luoping, GUO Xilong, ZHANG Jianming
DOI: 10.11660/slfdxb.20210216
This study conducts operation stability tests on a large Francis hydropower unit in four start-up modes–large acceleration open loop start of guide vanes, small acceleration open loop start of guide vanes, closed loop start of unit acceleration control, and open-plus-closed-loop start. We analyze and compare the stability of unit operation in these modes comprehensively. The results show that considering start-up time and unit stability, the first mode above is best. This study lays a basis for selecting and optimizing the start-up mode of Francis turbines.
2021 Vol. 40 (2): 158-166 [Abstract] ( 191 ) PDF (811 KB)  ( 602 )
167 Characteristics of compressibility and collapsibility of Ili loess under varying water content and dry density
NIU Lisi, ZHANG Aijun, WANG Yuguo, REN Wenyuan, ZHANG Wan
DOI: 10.11660/slfdxb.20210217
To reveal the deformation characteristics of the Ili loess in westerly wind regions, we conduct laboratory tests on its collapsibility with different dry densities and water contents using the double line method and a YS-I high-pressure consolidation apparatus, focusing on the characteristics of its compressibility and collapsibility. Results show that higher water content or smaller dry density leads to smaller yield stress, larger compression coefficient a1-2, and stronger softening on the δs-p curve. And collapsibility coefficient has negative linear correlation with water content or dry density, and it diminishes to nearly zero when the dry density is bigger than 1.6 g/cm3. We derive an expression of compressibility with the parameter of dry density and reveal that under different water contents, the normalized compressibility curve can be characterized using an exponential relationship of e/e0 versus lg(p/pc). For typical collapsible curves, we construct a four-parameter model that better reflects the softening characteristics of collapsible deformation curves, and present a normalized model formula including the parameters of dry density and water content. This work may be helpful to engineering construction in the westerly wind loess region of Central Asia.
2021 Vol. 40 (2): 167-176 [Abstract] ( 128 ) PDF (944 KB)  ( 432 )
177 Study of soil thickness regional evaluation using horizontal scales of fluctuation
DUAN Guijuan, LI Sa, SUN Liqiang, LIU Xiaolong, CHEN Wenwei
DOI: 10.11660/slfdxb.20210218
In recent years, evaluation of site geological conditions attracts more attention as more offshore projects are developed. Based on side-scan sonar data, this study calculates the horizontal scale of fluctuation using an improved space average method and an autocorrelation function method, and obtains a map of soil thickness distribution on the seabed over an offshore area by applying the ordinary Kriging method and the data of horizontal scale calculations. Results show that it is feasible to analyze the spatial autocorrelation and variability of soil thickness using the side-scan sonar data, and our scale calculation method is more stable and simpler. It is found that this scale falls in the range of 400-600 m for the soil layers in the study area. Generally, the accuracy of soil thickness distribution calculated using a data interpolation scheme that is determined by the calculated scales is satisfactory. However, evaluation errors may be quite big for those locations with small correlation distance, indicating a significant special variation in soil properties. To reduce such errors, the sweeping path of the side-scan sonar and the number of boreholes near these locations should be replanned to meet project needs.
2021 Vol. 40 (2): 177-186 [Abstract] ( 123 ) PDF (894 KB)  ( 437 )
187 Experimental study on consolidation-rheology characteristics of soil-aggregate mixture materials
ZHANG Yanyi, DENG Gang, WEN Yanfeng, WANG Junpeng, WAN Qiwei, WANG Xiaohui
DOI: 10.11660/slfdxb.20210219
The materials of most barrier dams comprise soil-aggregate mixture featured with a wide range of grading, and its rheological deformation is crucial to the long-term safe dam operation. This study conducts a consolidation-rheology test of three typical mixture materials with wide grading, using a large-scale testing apparatus. Analysis on the test results reveals that rheological strain increases with vertical stress following a logarithmic law, and the trend of increase is more prominent in the case of high vertical stress. We have examined the effect of material grading characteristics on rheological deformation, finding relatively small deformation in well-graded materials with large non-uniformity coefficients, while more significant deformation in materials with low grading characteristic values and high contents of fine particles. A four-parameter hyperbolic rheological model is constructed for time variations in the deformation; and it proves quite accurate as shown in our test results, well reflecting the consolidation-rheology characteristics of soil-aggregate mixture materials with wide grading.
2021 Vol. 40 (2): 187-194 [Abstract] ( 92 ) PDF (608 KB)  ( 415 )
195 Real-time quality control on lift thickness and pavement roughness of asphalt concrete core walls
LIU Donghai, ZHANG Yifei, LIU Qiang
DOI: 10.11660/slfdxb.20210220
In response to the pavement quality control requirements of asphalt concrete core walls, this study develops a real-time lift thickness detection and positioning device based on GNSS technologies and high-accuracy ultrasonic distance measurements, and formulates a real-time calculation method of determining lift thickness and pavement roughness. For dynamic monitoring and accurate positioning of lift thickness and pavement roughness, we also develop a corresponding real-time monitoring system that can display automatically the thickness and roughness profiles at the longitudinal sections of the core wall and broadcast an alarm to remind the construction personnel in time when the pavement is unqualified. Application to a real project shows very small errors in both the thickness and roughness measured by the device, meeting the required control accuracy. The proposed system achieves a real-time, remote, and synchronous monitoring of construction process, thus proving effective in the lean management and quality control of asphalt concrete core wall pavement.
2021 Vol. 40 (2): 195-203 [Abstract] ( 152 ) PDF (3700 KB)  ( 472 )
204 Effect of particle breakage on movement and heaping of debris flow
SHEN Zhihao, GUO Yutai, JIANG Hui, ZHOU Yuande
DOI: 10.11660/slfdxb.20210221
High-speed debris flow is commonly characterized by finite deformation, large displacement, and particle fragmentation. Using the particle discrete element method (DEM), this study simulates the size reduction of rock particles by adjusting the gradation distribution of the slide mass particles. We conduct parametric numerical simulations of a sloping site connected by a flat ground, and examine the influence of variable fragmentation factors on the movement and accumulation of non-cohesive granular assemblies. Simulations demonstrate that the difference in fragmentation degrees can induce a notable difference in the migration distance of the debris flow, and the stacking patterns of final deposits all exhibit a reverse segregation structure, while maintaining the original sequence to a certain extent. From analysis of particle velocity distribution during sliding, a dual-layer structure migration model is developed, and the simulations agree with the field observations and laboratory model tests of typical debris flow landslides. This study is most attractive for migration description of debris flows and prevention of relevant disasters.
2021 Vol. 40 (2): 204-213 [Abstract] ( 215 ) PDF (4282 KB)  ( 634 )
214 Permeability dependency of fly ash concrete in natural tidal environment
GAO Yanhong, SHAO Xinjie, ZHANG Yurong, FANG Runhua, ZHANG Junzhi
DOI: 10.11660/slfdxb.20210222
This study conducts an 840 d exposure experiment of fly ash concrete in natural tidal environment, and measures its water and air permeability coefficients and chloride diffusion coefficients using fly ash contents of 0, 20%, 30%, 40% and 50%. Then, we calculate the age reduction coefficients of the three coefficients and examine their dependency using a gray relative analysis method. Results indicated that all these coefficients decrease with the increasing exposure time or fly ash content and their dependency increases with fly ash content. Besides, a power function can be used to describe the time dependent water or air permeability, and the age reduction coefficient increases with fly ash content.
2021 Vol. 40 (2): 214-222 [Abstract] ( 143 ) PDF (858 KB)  ( 344 )
223 Second peak strength of steel fiber reinforced concrete under uniaxial tension
HUO Linying, BI Jihong, WANG Zhaoyao, ZHAO Yun
DOI: 10.11660/slfdxb.20210223
In uniaxial tensile tests, steel fiber reinforced concrete (SFRC) manifests two tensile strength peaks in the stress-strain curves, a phenomenon already revealed in a number of observations and different from the plain concrete case of a single strength peak. This study considers the effect of fibers bridging a crack using the bond-slip model for the interaction between the fibers and matrix, and formulates a relationship of steel fiber reinforcement stress versus crack width. The sum of the softening modulus of the matrix and the reinforcement modulus of the fiber is used for judging the occurrence of the second peak. When the sum is always non-negative, the SFRC stress-strain curve has a unique stress peak; otherwise, this curve will have two tensile strength peaks. Hence, we suggest three peak strength cases for SFRC, construct a finite element model to simulate its tensile tests, and examine the effects of fiber contents and fiber aspect ratios on its mechanical properties under the occurrence of concrete cracking. A calculation formula for the tensile strength of SFRC is given, which shows effective predictions.
2021 Vol. 40 (2): 223-233 [Abstract] ( 190 ) PDF (907 KB)  ( 408 )
234 Pixel-level shape segmentation and feature quantification of hydraulic concrete cracks based on digital images
REN Qiubing, LI Mingchao, SHEN Yang, ZHANG Ye, BAI Shuo
DOI: 10.11660/slfdxb.20210224
Concrete cracking is common in the main structures of hydraulic buildings, and crack detection is always crucial to hydraulic engineering safety appraisal. Shape segmentation and feature quantification are the main tasks of digital image processing technology that has been widely used in structural surface crack detection due to its advantages of high efficiency and low cost, but traditional image processing has the shortcomings of more manual intervention and weaker generalization ability. This paper describes a new method for pixel-level shape segmentation and feature quantification of hydraulic concrete cracks based on deep convolutional neural networks. This method is on the basis of U-net semantic segmentation architecture and incorporates the transfer learning technology. Specifically, it uses a pre-trained VGG16 network to enhance the encoder and extract multi-scale and high-level semantic information, and alleviates class imbalance problems by improving the cross-entropy loss function, so that the crack shape can be accurately segmented. Then, we present a set of algorithms based on the binarized segmentation mask and computer vision technology for calculating key geometric parameters such as crack area, length and width. To verify and evaluate this crack detection method, we generate an image dataset of hydraulic concrete cracking through numerical simulations and conduct comparative experiments demonstrating its effectiveness and superiority. The results indicate that its segmentation effect is significantly better than that of classical image segmentation methods, and its calculations of crack feature parameters meet the required detection accuracy. Thus, it is a new useful technique for quality control of hydraulic concrete structures.
2021 Vol. 40 (2): 234-246 [Abstract] ( 413 ) PDF (2536 KB)  ( 1287 )
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