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01 August 2020, Volume 37 Issue 8
    

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    SPECIAL CONTRIBUTION
  • LI Jia-zheng
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 1-8. https://doi.org/10.11988/ckyyb.20200049
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Many concrete face plates of rockfill dams in cold region should be built by one-off construction technique due to limits of duration and weather conditions. The present paper focuses on the impacts of properties of raw materials, environmental conditions, rockfill structure and properties of interaction zone, curing method as well as insulation measures on the cracking performance of concrete face plate. In association with field test data of cracks, the causes of a long concrete face plate in cold region built by one-off construction technique are symmetrically analyzed. Investigations reveal that high adiabatic temperature rising, temperature shrinkage, autogenous shrinkage and drying shrinkage are internal causes of the cracks of concrete face plate in construction stage. Meanwhile, high casting temperature, large temperature difference between day and night, low temperature of maintenance water, and also temperature reduction in winter, as environmental causes, accelerate the crack of concrete face plate. Constraints of interaction zone exert significant impacts on the state, level and distribution of stress. Emulsified asphalt is helpful to reduce the constraints of interaction zone and brings down the cracking risks of concrete face plate.Elements including properties of raw materials,structure of rockfill and interaction zone,and environmental causes should be seriously considered in the design stage,construction stage and curing stage of concrete face plate.
  • RIVER-LAKE SEDIMENTATION AND REGULATION
  • LÜ Chao-nan, JIN Zhong-wu, LIN Mu-song, LI Qiu-li, WANG Yu-xuan
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 9-15. https://doi.org/10.11988/ckyyb.20190573
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    As an important tributary of the upper Yangtze River, Minjiang River provides a pivotal support for the social economic development in western Sichuan and Chengdu plain. The overall hydropower development in the Minjiang River basin took place slightly later than that in other major tributaries of the Yangtze River. In recent years, reservoir construction project increases unceasingly in the Minjiang River basin, giving rise to variations in the water and sediment condition. In this paper, the characteristics of reservoir construction and water-sediment transport as well as their interrelations are preliminary examined according to flow-sediment process lines and accumulative runoff-sediment load curves based on measured data. Results demonstrated that the number of reservoirs and the total storage capacity have surged since 1970 and 2005, respectively. Reservoirs are constructed from the mainstream to tributaries, with the number of reservoirs under construction declining while high dams and large reservoirs increasing. As dam construction technology improves, earth dam which is easy to construct is gradually changed into other dam types with high difficulty. Moreover, due to the enhancement of reservoirs’ regulation ability and sediment holding function, the runoff and sediment transport in main flood season of the basin have been flattening. Annual runoff and annual sediment transport both saw a downward trend after 1990, of which the annual sediment transport has been decreasing more obviously. Recently, the change of annual sediment transport volume at Gaochang station is in a negative correlation with reservoir construction. Such correlation intensifies with the further increase in the total capacity of reservoir in Minjiang River basin, and is more evident in flood season.
  • LI Zhi-wei, TANG Tao, YUAN Xin-ya, YU Guo-an
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 16-21. https://doi.org/10.11988/ckyyb.20190718
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    Geological disasters occur frequently in the Yarlung Tsangpo Grand Canyon, particularly in Yigong Tsangpo River and Parlung Tsangpo River where landslides, avalanches, and debris flows easily block the rivers and give rise to barrier lakes. According to multi-annual Landsat imagery of Yigong Lake, Guxiang Lake, Ranwu Lake, and Tianmo Gully as well as the longitudinal profile fitted by simple function, we analyze the morphological processes of upstream riverbed and its geomorphological significance in association with field investigation in 2011-2017. Taking Yigong Lake as an example, when water depth of the lake increases from 4 m to 8 m, we roughly estimate that the bedload transport rate per channel width increases by about 3 times, which however decays rapidly along the course. Thus, sediment deposition within the lake would be unavoidable. Meanwhile, unstable bars in flood period are eroded and split into irregular bars, which leads to the continuous change of bed morphology in the lake.The research findings provide a new understanding on the response of river morphology to barrier dams.
  • WATER RESOURCES AND ENVIRONMENT
  • DENG Hong-wei, WANG Peng
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 22-28. https://doi.org/10.11988/ckyyb.20190679
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    Regional water environmental carrying capacity (WECC) is of crucial significance for the formulation of sustainable development policy. In line with the current situation of water environment in Enshi Prefecture, 15 indexes in regards to society, resource environment, and economy were selected to constitute an index system for evaluating WECC. In association with the spatial analysis function of geographic information system(GIS), the subjective and objective weights of each index were given using the sum of deviation square, and each index was rasterized and superimposed in GIS to obtain the quantitative value of WECC and the spatial distribution map of WECC of Enshi Prefecture in 2017. Results suggest that the overall WECC of Enshi Prefecture is at a moderate level. The area proportion with WECC of 5 grades (excellent, good, moderate, inferior, and very inferior) is 1.23%, 27.24%, 42.62%, 19.17%, and 9.74%, respectively. The WECCs of Laifeng, Xuanen, and Hefeng counties are the highest, and those of Jianshi, Badong and Xianfeng are slightly lower, while the WECCs of Lichuan and Enshi are the most inferior.
  • LIU Shu-feng, CHEN Ji-chen, GUAN Shuai
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 29-34. https://doi.org/10.11988/ckyyb.20190462
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    The water storage and power generation of small hydropower on small and medium-sized rivers not only brings about economic benefits but also affects the environment. The ecological flow calculation and ecological operation of small hydropower are particularly important to refrain from dehydration in the downstream. With Hengxi Hydropower Station on Yangxi River as a case study, we first of all calculate the runoff according to the relation between rainfall and runoff depth, and further calculate the ecological flow of wet year, flat year, and dry year respectively using the modified flow duration curve (FDC) method. Subsequently we calculate the ecological operation in consideration of ecological flow, power generation, and irrigation. Results reveal that we could accurately calculate the runoff of Hengxi Hydropower Station by using the relationship between rainfall and runoff depth. In the absence of operation, the inflow of Hengxi Hydropower Station could not fully meet the requirements of ecological flow calculated by the modified FDC method at each level year. The modified FDC method is applicable and rational. After ecological operation, the dam-crossing discharge of Hengxi Hydropower Station could meet the demand of aquatic ecology and maximize the benefit of power generation. The research results offer reference for promoting the sustainable development of hydropower, balancing the benefits of power generation and ecology, as well as the healthy management of small and medium-sized rivers.
  • ZOU Shan, LI Yu, CHEN Jin-feng, ZHANG Guo-xue, ZHOU Xin-chun
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 35-41. https://doi.org/10.11988/ckyyb.20190524
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    Affected by multiple factors such as climate change, cascade reservoir operation, and tributary influx, the temporal and spatial distribution of water temperature in the segment of the Yangtze River from Panzhihua to Yichang has changed remarkably, which will surely have a profound impact on the river ecosystem. The water temperature data in nearly 60 years(1956-2016) of typical hydrological stations in mainstream and tributary were selected for analysis. The characteristics of spatial-temporal variation and distribution of water temperature along this segment were studied by using attribution analysis and multi-scale comparative analysis. Results revealed an apparent warming trend in the mainstream of Panzhihua-Yichang segment, while in the tributary Minjiang River, as affected by air temperature, the water temperature underwent a continuous drop by 1 ℃ between 1956 and 1990, and then gradually recovered. The range of the water temperature during a year decreased annually, with a declining range of 0.38-1.46 ℃ per decade, which means that the process of water temperature during a year tends to flatten. The construction of cascade reservoirs reduced the water temperature in the downstream rivers in spring and summer while increased in autumn and winter at Pingshan and Yichang stations. The changes in April and December after the impoundment were the largest, amounting to -2.6 ℃ and 4 ℃, respectively. The distribution pattern of water temperature along the stream was generally stable: the water temperature of the Panzhihua-Pingshan segment increased ceaselessly by 2 ℃; affected by large amount of low-temperature water (occupying over 50% of the discharge) from the Minjiang River, the water temperature of the Pingshan-Zhutuo segment dropped by 0.6 ℃; the high-temperature water in the Jialing River and the low-temperature water in the Wujiang River have little impact on the water temperature of the Zhutuo-Yichang segment due to small proportion of discharge.
  • WU Zhen-hui, MEI Ya-dong, CAI Hao
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 42-48. https://doi.org/10.11988/ckyyb.20190487
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    A dynamic optimal allocation method for total amount control of water resources is proposed in this paper to determine the annual gross control index of water consumption and to rationally control water allocation according to inflow. With Fuhe River drainage basin as a case study, a model for optimal allocation of water resources is established with minimizing the water shortage in remaining stage (operation stage) as the objective, and water demand in water use area as well as flux requirements for control sections as constraints. The control index is real-time adjusted through the dynamic operation mode “forecast-decision-implementation-renewal”. Result shows that the water shortage rate in the water use area declines by 3.8%-25.3% when inflow scenario (IS) changes from wet to dry, while the water use in remaining stage is always controlled within the total amount control index when dry IS turns to wet. The annual total amount control index of water consumption calculated by the present method effectively adapts to different water conditions in the year, and meanwhile instigates or limits the supply of water according to different water supply conditions.
  • ZENG Kai, WANG Jia-sheng, ZHANG Yun-chao, ZHANG Lin, YANG Qi-hong
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 49-53. https://doi.org/10.11988/ckyyb.20190419
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    According to measured data of water level and water quality at typical sites of Huayang River and Lake Group, we analyzed the influences of spatial and temporal changes of water level on water quality indicators and the correlation between water level and water quality using the Spearman method. Results demonstrated that affected by the incoming water quality of the Yangtze River, the water quality of Huyang River and Lake Group was inferior in the west while superior in the east. In interannual scale, the water quality of Longgan Lake, Huanghu Lake, Bohu Lake and Daguan Lake fluctuated from 2015 to 2018, and particularly in 2018, the water quality of Longgan Lake, Huanghu Lake and Bohu Lake were inferior; in annual scale, the pollutant concentration index of each lake was larger in dry season than that in wet season. In addition, water level fluctuation is negatively correlated with the concentration of TN, TP and COD. The average correlation coefficient is about -0.43, -0.41, -0.09, respectively, and the absolute values are all smaller than 0.5.
  • FLOOD PREVENTION AND DISASTER REDUCTION
  • LI Chang-wen, YOU Zhong-qiong, XU Zhao-ming
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 54-60. https://doi.org/10.11988/ckyyb.20190396
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    Tonle Sap Lake is the largest lake linked with Mekong River. The variations of water level and area exert vital impact on the structure and function of Tonle Sap Lake. Identifying the evolvement rule of water level and area is of guiding significance for flood control and drought relief as well as eco-environmental protection in Tonle Sap Lake and the Mekong Delta. According to long series of daily water level data of Phnom Penh Port, Prek Kdam and Kampong Luong stations and topographic data of lake area, we analyzed the inter-annual and annual variations of water level and area of Tonle Sap Lake. Results reveal that the water level of Tonle Sap Lake raise and fell slowly, with the rising duration shorter than falling duration and rising rate higher than falling rate. The water level of Tonle Sap Lake fluctuated frequently between years, with the annual average water level, annual maximum water level, annual water level range, annual flood duration, annual average flood level and daily rising rate all showing slight downward trend, while the annual lowest water level, water withdrawal days and daily falling rate showing upward trend. The annual water level and area of Tonle Sap Lake changed with a single peak value. The lowest water level was in May, when the average water level was 1.51 m and the corresponding area 2 487 km2, the measured minimum water level 1.11 m and the corresponding area 2 053 km2; the water level reached the maximum value in October, when the average water level was 8.70 m and the corresponding area 12 768 km2, the measured maximum water level 10.54 m and the corresponding area 15 261 km2. Multi-year average water level range of Tonle Sap Lake was 7.63 m and the corresponding area range was 10 628 km2.
  • ENGINEERING SAFETY AND DISASTER PREVENTION
  • HAN Fei, NIU Rui-qing, LI Shi-yao, ZHAO Ling-ran, BAI Xing-yu
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 61-68. https://doi.org/10.11988/ckyyb.20190638
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    Frequent landslide disasters in the Three Gorges Reservoir area threaten the safety of people’s lives and property. Predicting landslide displacement rationally and effectively is of crucial significance for reducing property losses and protecting people’s lives. In view of the limits of conventional decomposition methods, the variational decomposition method which could control the number of decomposition modes was introduced into the decomposition of displacement time series. The Baijiabao landslide in the Three Gorges reservoir area was taken as a case study. The parameters are compared to improve the accuracy and effectiveness of the decomposition model. Moreover, a deep confidence network model involving landslide triggers was established to predict the displacement subsequences, and the results of all subsequences are reconstructed to obtain the total displacement prediction value. The mean average error of predicted total displacement is 3.657 mm, and the mean average percentage error is 0.010%, indicating a high accuracy.
  • ROCK-SOIL ENGINEERING
  • WANG Bin, ZHU Jie-bing, ZHANG Zhen-jie, ZHANG Li-jie
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 69-74. https://doi.org/10.11988/ckyyb.20191526
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    The classification of engineering rockmass is a most basic content in rock mechanics and rock engineering application research area. However, current applied rockmass classification system doesn’t cover the rockmass classification method for surrounding rockmass under special geological conditions, such as high ground temperature and high temperature gradient. On background of a hydropower station construction in south Xinjiang, a segment of diversion tunnel with high ground temperature is chosen for surrounding rockmass classification research. On the basis of field geological mapping, in-situ acoustic test and laboratory rock mechanics test results, the RMR, GSI, BQ and HC systems are applied respectively to the rockmass classification and rockmass quality evaluation for the research segment. According to actual surrounding rockmass grade as well as qualitative and quantitative grading results, the influence factors and threshold indexes of high ground temperature are proposed. The evaluation method of surrounding rock quality method of tunnel under complex geological conditions is obtained. Results show that the rockmass quality evaluation grade results with the proposed method are reduced by 1/4~1/2 grade, much closer to the actual grading results.
  • DONG Long-jun, ZHANG Ling-yun
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 75-81. https://doi.org/10.11988/ckyyb.20190430
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    The change in b-value of rock acoustic emission is an important precursors of rock fracture. However, b-value is affected by artificial settings such as sample size, start amplitude and amplitude interval. It is of great significance to quantify the error of b-value. In this paper, the maximum likelihood method and the least squares method are employed to calculate the b-value of the rock fracture acoustic emission amplitude catalogues composed of random numbers with different sample sizes, start amplitudes and amplitude intervals. The results distributed within the error are recorded as valid data, and the error of b-value is analyzed according to the proportion of valid data. The result is verified using the acoustic emission amplitude catalog of indoor triaxial compression test data. For maximum likelihood method, the valid data proportion reduces as the sample size increases, while augments as the start amplitude increases. For least squares method, as sample size increases, valid data proportion first increases and then declines. The most valid data is obtained when the sample size is around 2000. Given the same amplitude interval, as the start amplitude increases, the corresponding optimal amplitude interval reduces from 22 dB to 18 dB. This study provides a conducive reference for the reasonable calculation of b-values of rock fracture acoustic emission.
  • CAO Wei-ping, ZHAO Cheng, LI Yuan, ZHANG Wei-wei
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 82-88. https://doi.org/10.11988/ckyyb.20190515
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    Batter piles are subjected to horizontal loads and meanwhile uplift loads. To investigate the influence of uplift load on the horizontal bearing behavior of batter piles, we conducted indoor model tests on two groups of batter piles subjected to different uplift loads and vertical pile subjected only to horizontal load as control group. According to test result we examined the effects of uplift load on horizontal displacement and horizontal bearing capacity of the top of batter pile, compared the bending moment and shearing force between vertical pile and batter pile, and also analyzed the effects of uplift load on the internal force and frictional resistance of positive and negative batter piles. When uplift load increased from 12.5% to 75% of the horizontal ultimate bearing capacity of vertical piles, the horizontal bearing capacity ratio of positive batter piles increased by 21% while that of negative batter piles decreased by 25%. Uplift load augmented the axial force of both positive and negative batter piles. The larger the uplift load, the greater the axial force of pile. Uplift load also reduced the bending moment and shear force of positive batter piles, hence improving their ability to resisting moment and shear force, while weakened the ability of negative batter piles to resisting bending moment and shear force by increasing the bending moment and shear force. Both positive batter piles and negative batter piles witnessed an upward frictional resistance on the lateral surface of the pile body in the upper section, and downward frictional resistance in the lower section. With the increasing of uplift load, such side frictional resistance increased gradually.
  • YE Hong, CHEN Yan-ping
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 89-94. https://doi.org/10.11988/ckyyb.20190504
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    In the purpose of studying the seismic behavior of pressure-type cable in weak rock and soil under earthquake more accurately, the expressions of prestress and prestress loss under the coupling effect of prestress of anchor rope and creep of rock and soil mass were derived based on the material relaxation of steel strand subjected to long-term load. Furthermore, the expressions of equivalent compressive stress and equivalent shear stress of the anchorage segment of pressure-type anchor cable under circular uniform load were derived using pseudo-static method, Mindlin basic solution and integral simplification method. Case study demonstrated that the loss of prestress was large in the initial stage, stabilized in mid-stage and changed little in later stage, with the loss rate declining consistently. The equivalent stress of mortars in anchorage segment concentrated mainly within 0.5 m from the pressure plate. The maximum equivalent stress was in 0.1 m from the pressure plate rather than on the contact surface between pressure plate and mortars. The research findings enriched the theoretical research in regards to seismic design of pressure-type anchor cables, and offered some references for the reasonable seismic design of slope strengthened with pressure-type cable.
  • WEI Zi-yang, HUANG Zhi-hong, MU Rui, HUANG Yan-sen, PU Shao-yun, WU Ning-bo, WANG Bo
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 95-100. https://doi.org/10.11988/ckyyb.20190552
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    The low recycling rate of ever increasing waste tire has brought about severe environmental problems. In this research we prepared mixed soil samples by adding waste tire rubber powder into red clay, and examined the compaction strength, shear strength and permeability of the mixed soils with varied rubber powder content (0%, 3%, 8%, 15%, 25%) and water content via standard light compaction test, equivalent compaction test, direct shear test and penetration test. Results unveiled that (1) the maximum dry density of red clay mixed with rubber powder was lower than that of original red clay, and the maximum dry density decreased with the increase of rubber powder content. (2) With the growth of rubber powder content, the optimum water content augmented in standard compaction test but reduced in equivalent compaction test. (3) When rubber powder content was lower than 15%, both the shear strength and internal friction angle of the mixed soil climbed with the increase of rubber powder content, showing strain hardening features. (4) In standard compaction test, when rubber powder content was 8%, the permeability rate of mixed soil rarely changed, while when rubber powder content was 15%, the permeability rate soared with an increasing rate of 97.3%. The research findings offer reference for the recycling of waste rubber powder and the engineering application of modifying red clay with rubber powder.
  • LIU Peng-cheng, HUANG Wu-feng, BAO Tai, GUO Jian-qiang, MU Lin
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 101-105. https://doi.org/10.11988/ckyyb.20190505
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    Water-rock interaction has always been a hot topic of research. Water-rock interaction deteriorates rock properties and affects the strength of rock. In this paper, the strength and deformation of argillaceous dolomite undergone different dry-wet cycles are investigated through uniaxial and triaxial compression tests. Moreover, the damage statistic constitutive model of rock under dry-wet cycles is derived based on the continuous damage mechanics and statistical theory. Results reveal that: the peak strength of argillaceous dolomite declines with the proceeding of cyclic drying and wetting. In uniaxial compressive test, the total deterioration degree of argillaceous dolomite increases in general with the increase of dry-wet cycles, while the staged deterioration degree and average deterioration degree gradually reduces and tends to be stable. In triaxial compressive test, the total deterioration degree of argillaceous dolomite decreases before increasing with the climbing of confining pressure. Larger number of cycle has a greater effect on the deformation of rock than higher confining pressure does. The elastic modulus of argillaceous dolomite also declines basically with the proceeding of cyclic drying and wetting. Comparison between theoretical curves and experimental curves demonstrates that the constitutive model well reflects the triaxial stress-strain relationship of rock, hence is rational.
  • ROCK-SOIL ENGINEERING
  • LIU Xue-ying, WANG Yong-hong, ZHANG Ming-yi, SUN Shao-xia, SANG Song-kui, MIAO De-zi
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 106-112. https://doi.org/10.11988/ckyyb.20190345
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    Jacked pipe has been widely used in practical engineering. The excess pore water pressure at the pile-soil interface has a great influence on the performance of jacked pile. Most current researches focus on the distribution of excess pore water pressure in the soil around the pile rather than the real situation of stress at the pile-soil interface. In this paper, by drilling holes in pile body and embedding silicone piezo-resistance pore water pressure sensor, static pile pressure test was conducted on two groups of model piles in clayey soil. The variations of pore water pressure and excess pore water pressure at the pile-soil interface were investigated. The pore water pressure generated at the pile-soil interface during pile jacking has been successfully monitored for the first time by the silica-piezo-resistance sensor. The pore water pressure and excess pore water pressure of pile-soil interface both increased with the growth of pile jacking depth. In the meantime, the excess pore water pressure generated in the process of pile jacking was relatively large, up to 4.21 kPa, which was about 75% of the effective overburden soil weight. In practical engineering, the relatively large excess pore water pressure generated in the process of pile jacking should be paid attention to. The excess pore water pressure at the same depth dissipated, and such dissipation attenuated with the increase of depth. In practical engineering, effective measures should be taken to prevent from excessive excess pore water pressure. The test results offer reference for static pressure pile construction and theoretical research on pile-soil interface.
  • WANG Wei-guang, HAO Xiu-wen, LI Wan, YAO Zhi-hua
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 113-119. https://doi.org/10.11988/ckyyb.20190599
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    The influence of compaction mode on the mechanical deformation performance of coral sand foundation is examined by means of in-situ detection and settlement monitoring. The reinforcement project for coral sand foundation of an airport is taken as a case study. In line with the engineering properties of reclaimed coral sand foundation, vibratory compaction method and impact compaction method are employed in foundation treatment in different test areas. Results show that the CBR (California Bearing Ratio) could reach 38% after 20 times of vibration compaction, whereas after 30 times of impact rolling, the CBR value is only 28%. After 30 times of vibration rolling, the uncorrected characteristic value of foundation bearing capacity is above 270 kPa, the response modulus of soil foundation is up to 106.68 MN/m3, and the rolling-induced settlement deformation tends to be stable. Under the same number of times of compaction, the bearing capacity and deformation resistance of the foundation after vibration compaction are obviously higher than those after impact compaction, indicating that vibration compaction is more suitable for coral sand foundation treatment than impact compaction. The in-situ immersion test in the vibratory rolling area shows that coral sand foundation is not easily affected by surface water changes in terms of deformation properties. The research results can be used as reference in guiding the foundation treatment of reclaimed coral sand foundation and similar projects.
  • ZHANG Pan, XU Yong-fu, WU Xiao-tian
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 120-125. https://doi.org/10.11988/ckyyb.20190375
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    Due to transpiration, the uptake of water by plant root plays a vital role in the stability of soil slope. To quantify such effect, the water uptake by four types of plant roots(uniform, triangular, exponential, and parabolic) were simulated using finite element method,and the effects of root’s geometry and depth on pore water pressure were also analyzed. Results demonstrate that with the proceeding of water uptake, shallow pore water pressure gradually decreases, while safety factor climbs, the shear strength of unsaturated soil increases, and slope stability enhances. The envelopes of pore water pressure and safety factor ratio of the four types of plant roots are basically the same as the root distribution’s shape function. The exponential root has the most superior reinforcement effect on slope because of its lowest ground surface pore water pressure and largest safety factor ratio. Given the same total root amount, the greater the root depth is, the larger the influence zone is, and the lower vegetated soil’s shear strength and smaller factor of safety increment.
  • PU Quan, WU Dao-yong, ZUO Shuang-ying, ZHANG Yan-zhao, YANG Chong
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 126-130. https://doi.org/10.11988/ckyyb.20190307
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    The dispersion status of Guiyang red clay in different media environment was accurately tested in the present research. In the light of the effect of Guiyang red clay’s special microstructure on particle size distribution, particle size analysis test was carried out using mechanical grinding method, ultrasonic method, and chemical dispersion method, respectively, to study the particle size distribution law. Results unveil that the dispersion of soil particles treated with chemical reagent is better than that with mechanical grinding or ultrasonic wave. Five types of chemical reagents were further used for particle dispersion, among which sodium hexametaphosphate ((NaPO3)6), as a strongly alkaline and weakly acid salt, has the optimum dispersion effect. Moreover, concentration, temperature, and test dose were selected as influential factors to obtain the most favorable dispersion conditions for Guiyang red clay: (NaPO3)6 solution with a concentration of 2% and dose of 10-15 mL at a temperature around 40 ℃. On such basis, the dispersion mechanism of Guiyang red clay was expounded: cemented agglomerations, a particular spatial structure, were formed among the micro-structural cells of Guiyang red clay via free iron oxide. Free iron oxide is of strong activity and is prone to be hydrated under varying environment, thus affecting the fastness of cemented agglomerations, and therefore is a key factor leading to different dispersion effects.
  • HYDRAULIC STRUCTURE AND MATERIAL
  • NIU Jian-gang, WANG Meng-yu, LIU Xiao, LUAN Rui-lin
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 131-136. https://doi.org/10.11988/ckyyb.20190616
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    In order to investigate the joint strengthening effect of Concrete Canvas (CC) and Carbon Fiber Reinforced Plastic (CFRP) on the mechanical properties of reinforced concrete square column, we designed axial compression tests on eight groups of sixteen CC+CFRP reinforced columns, and examined the influences of CFRP band constraint, full constraints and the number of CFRP layers on the failure mode, bearing capacity and ductility of CC+CFRP reinforced columns. Results reveal that the mechanical properties of reinforced concrete square columns are remarkably affected by the restraint mode and quantity of CFRP layers under joint strengthening. CFRP band wrapping is superior to full wrapping in terms of improving bearing capacity, and the bearing capacity of column strengthened by two layers of CFRP improves the most. In terms of deformation, CC ameliorates the failure form of the column, and enhances the ductility and deformation capacity of the column. The research results are of referential value to reducing the corrosion of reinforced steel and upgrading the durability of concrete structures.
  • JIANG Ping-wei, FANG Jiang-hua, PANG Jian-yong, HUANG Jin-kun
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 137-141. https://doi.org/10.11988/ckyyb.20190646
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    The microstructure of plant fiber shotcrete (PFSC) is analyzed by means of scanning electron microscopy (SEM) in a purpose of investigating the influence of plant fiber dosage on the mechanical properties and thermal conductivity of PFSC. Compared with those of plain shotcrete, the compressive strength and splitting tensile strength of PFSC dosed with 2.0 kg/m3 plant fiber increase by 17.35% and 20.26%, respectively, while the thermal conductivity reduces by 20.61%. SEM analysis shows that plant fiber in low-volume well disperses in the interior of the shotcrete and adheres to the concrete matrix. However, large content of plant fiber agglomerates in the shotcrete, leading to more internal defects of PFSC. According to the comprehensive mechanical properties test results, we recommend that the plant fiber content should not exceed 2.0 kg/m3.
  • XING Yue, TIAN Zheng-hong, DU Hui
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 142-149. https://doi.org/10.11988/ckyyb.20190644
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    An intelligent evaluation method for the interlayer bonding quality of roller compacted concrete (RCC) dam is proposed in the light of reliable evaluation and dynamic control of interlayer bonding quality of RCC dam. (1) An evaluation indicator system with moisture content and compaction degree of RCC thermal layers as evaluation parameters and splitting tensile strength at 90 d-age of RCC core samples as evaluation target is established to reasonably characterize the interlayer bonding quality in the field. (2) The inverse distance weighted (IDW) interpolation method was employed to simulate the discrete parameters obtained by sampling detection with self-developed intelligent devices in the entire work area of RCC dam, and the spatial uncertainty was analyzed quantitatively by comparing the parameter simulation accuracy of sample sequences with different quantities and different mesh sizes. (3) The intelligent evaluation model for the interlayer bonding quality was established based on Bagging algorithm integrated with back-propagation artificial neural network (BP-ANN). The model was applied to the dynamic evaluation of the interlayer bonding quality of a typical construction warehouse of Wunonglong RCC Dam. Results suggest that the present method accurately and dynamically evaluates the interlayer bonding quality in consideration of spatial uncertainty, and also integrates the intelligent perception, transmission and evaluation of construction information.
  • 2020 ANNUAL CONFERENCE (ACADEMIC SEMINAR) OF SURVEY SPECIALIZEDCOMMITTEE OF CHINESE HYDRAULIC ENGINEERING SOCIETY
  • SI Fu-an, LI Kun, DUAN Shi-wei
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 150-154. https://doi.org/10.11988/ckyyb.20200567
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    Commonly applied methods of classifying the surrounding rock of hydraulic tunnels are based on the construction of shallow buried tunnels and drilling and blasting. Such classifications show poor adaptability to deep buried long hydraulic tunnels constructed with tunnel boring machine (TBM). On the basis of classification methods in China and abroad, we propose a comprehensive classification method which describes not only the surrounding rock stability, and also the types and levels of geological risks for deep buried long hydraulic tunnels constructed with TBM. According to the characteristics of deep buried long hydraulic tunnels and the main geological risks that may be encountered during TBM construction, we select some major assessment factors inclusive of surrounding rock stability, high geostress risk, groundwater risk, as well as excavability. The proposed method is applied to a water conveyance project in Xinjiang and has achieved good result. The research offers technical support for the excavation and support design of deep buried hydraulic tunnel, and also can be regarded as a basis for targeted treatment of possible geological risks during TBM construction.
  • ZHOU Bing-qiang, HUANG Can-xin, WANG Tuan-le, HUANG Xiao-quan, LIU Ke, XU Qi
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 155-160. https://doi.org/10.11988/ckyyb.20200558
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    As the most dominant means to tackle reservoir leakage, anti-seepage curtain has been broadly used in the construction of hydropower projects. In recent years, many hydropower projects have been built in southwest China where carbonate strata develops widely with complex karst conditions, giving rise to frequent grouting abnormalities such as excessive amount and leakage in construction period of anti-seepage curtain. As a giant hydropower station built in typical carbonate rock area, Wudongde hydropower station has a maximum dam height of 270 m and a largest water retaining head of about 160 m, with large curtain scale, high water head, and complex geological conditions. In view of the local grouting abnormality at 850 m grouting adit on the left bank of anti-seepage curtain of the dam, we propose to employ a “3D geological information visualization of grouting engineering analysis system (GEAS 3D)” for examining the scope of abnormal area, the engineering geological characteristics and grouting characteristics in association with traditional means such as grouting hole, special investigation hole, construction branch hole and geophysical detection so as to provide basis for targeted treatment. This paper offers a solution for grouting anomaly comprehensive analysis based on “geological BIM plus grouting information” analysis management platform, which can be used for reference for similar projects.
  • GENG Hong-bin
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 161-165. https://doi.org/10.11988/ckyyb.20200568
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    The compactability of soil plays a very important role in water conservancy project. In order to study the correlation between fine-grained soil’s compactability and particle composition , according to eight water conservancy projects since 2017, we collected data of compaction test and grain size test. Most test samples are collected from a range of about 200 km between Yangtze river and Huaihe river in Anhui province. The correlation between maximum dry density, optimum water content of fine-grained soil and sand-silt-clay data was examined by simple linear regression and binary linear regression. A binary linear regression result was obtained by using clay-silt content as independent variable and maximum dry density and optimum water content as dependent variable while excluding the data of clay content larger than 37%. Results suggest that particle composition is the major factor affecting the compactability of fine-grained soil, while water and gas in soil also have some effects on the compactability at the same time. A good correlation was found between maximum dry density and optimum water content and soil composition while fine-grained soil content is in the range from 10% to 37%. This study will help us to understand the compactability of fine-grained soil meanwhile avoid poor accuracy and artificial factor during compaction test and grain size test.
  • YAO Zhen-guo, XU Wen-jie, LUO Yan-ting, WANG Hong-fei
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 166-169. https://doi.org/10.11988/ckyyb.20200573
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    Landslide surge is a grave disaster in the operation of reservoir. The prediction of landslide surge requires an analysis of the sliding speed of the landslide. With a high-level loose landslide body in a reservoir as an example, the sliding speed of the landslide body was calculated using traditional empirical formula and discrete element method (DEM) respectively. Traditional method has some limitations in calculating the sliding speed of loose landslides, while DEM is superior in analyzing the process of landslide surge of high-level loose landslide as the DEM-simulated deformation process is basically consistent with qualitative instability process. According to DEM-calculated deformation and failure process of landslide at different instances and the velocity of DEM spherical particles,the speed of unstable materials was not large in the incipience of sliding under the action of gravity, but increased continuously during the movement on bedrock slope, and finally reached about 40 m/s upon entering water. The present method has advantages in analyzing the disaster process of high-level loose landslides and provides a good reference for similar engineering problems.
  • WEI Zhen-jing, YU Jing-zong, ZHANG Dong-dong
    Journal of Changjiang River Scientific Research Institute. 2020, 37(8): 170-174. https://doi.org/10.11988/ckyyb.20200563
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    The main dam of the Datengxia hydro-project is a concrete gravity dam. According to survey and excavations, many soft and weak interlayers develop in the dam foundation rockmass of the release sluice segment. The soft and weak interlayers are characterized by poor performance, good continuity, gentle dip towards the downstream left bank, forming a deep sliding boundary of the dam foundation. In this study, the mechanical parameters of structural plane are determined by analyzing the distribution and properties of these soft interlayers, and the slid patterns are determined by the spatial combination of soft interlayers and faults. Moreover, the sensibility of sliding surface to depth is analyzed using rigid limit equilibrium method, and the deep anti-sliding stability of dam foundation is calculated and evaluated. According to the calculation results, treatment measures are put forward for dam segment which do not meet requirements. This research provides a typical case for the study of deep anti-sliding stability of gravity dams in large hydro-projects, and also provides enlightenment and reference for similar projects around the world.