01 February 2020, Volume 37 Issue 2

    

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SPECIAL CONTRIBUTION
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  Practices of Health Assessment and Protection of the Yangtze River

  CHEN Jin

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 1-6. https://doi.org/10.11988/ckyyb.20191470

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  Yangtze River is a large river system and is rich in biodiversity. Its health status not only affects the sustainable development of the basin economy and society, but also receives wide concerns from both China and abroad. In this paper, the theories and practices of river health assessment in China and abroad are reviewed, and on this basis, the methods and standards of river health assessment suitable for the Yangtze River are discussed. The change of water environment and water ecology of the Yangtze River in the recent decade are analyzed in terms of two indexes: standard-reaching rate of water functional zone, and fish diversity. Last but not the least, the health progress of the Yangtze River after a series of great protection actions in recent years is summarized. The health assessment of the Yangtze River can be divided into different spatial and temporal scales according to management needs. Single index assessment or multi-index comprehensive assessment can be performed according to the integrity of data. The water quality of the Yangtze River has been improved continuously; the water quality in lakes and reservoirs and the biodiversity in rivers and lakes have begun to stabilize; the excessive disturbance on rivers and lakes by human beings has been restrained. Nevertheless, the improvement of water quality in lakes and reservoirs and the restoration of biodiversity still need to be carried out for a long time.
RIVER LAKE SEDIMENTATION AND REGULATION
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  Evaluation of the Impact of Three Gorges Reservoir on Three Outlets of Jingjiang River

  ZHAO Qiu-xiang, FU Xiang, SUN Zhao-hua

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 7-14. https://doi.org/10.11988/ckyyb.20181020

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  The three outlets of Jingjiang river, as the link between Dongting Lake and Jingjiang River, has always been the key point of flood control, shipping, water environment changes and water resources utilization in Dongting Lake area. In this paper, the diverted flow rates from Jingjiang River in the presence and in the absence of the Three Gorges Reservoir were calculated using a flow diversion model of the three outlets of Jingjiang River. The observed and corresponding naturalized data of daily flow rate at Zhicheng station during 2008-2015 were taken as the model inputs. Moreover, the influences of the Three Gorges Reservoir on the runoff, diversion ratio and diverted flow of the three outlets (including the comprehensive influence of runoff regulation and river channel adjustment) were discussed, and in particular, the influence of river channel adjustment on the runoff of the three outlets was expounded. In the presence of the Three Gorges Project, under the comprehensive influence of runoff change and river channel topography regulation, in pre-flood season the multi-year average diverted runoff and diversion ratio increased by 28.17% and 9.59%, respectively, and the zero-flow situation of the outlets basically remained unchanged; in flood period the annual average runoff decreased by 2.11% while diversion ratio increased by 0.56%, with the zero-flow situation changed little; in post-flood season, the multi-year average diverted runoff and diversion ratio decreased by 33.87% and 19.84% respectively, with barely no change in the zero-flow situation at Songzi and Taiping whereas increased and advanced days of zero-flow at Ouchi; in dry season, the multi-year average diverted runoff increased by 8.60%, the multi-year average diversion ratio decreased by 2.93%, and the multi-year average number of days of zero decreased by 30.43 days and 6.80 days respectively at Songzi and Ouchi, but increased by 30.86 days at Taiping. In addition, the adjustment of river channel topography increased the runoff of Jingjiang River by 2.73% in flood season, and reduced the runoff of Jingjiang River by 16.62%, 3.10%, and 18.49% respectively in pre-flood season, pre-flood season and dry season. The research findings lay a foundation for the study of lake drought and water resources utilization and protection in the Dongting Lake area as well as the operation of Three Gorges Reservoir.
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  Abrupt Changes of Hydraulic Characteristics in Curved Bifurcated Channel under Bankfull Discharge

  ZOU Ji, LIU Ya, LU Jin-you

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 15-20. https://doi.org/10.11988/ckyyb.20181012

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  The hydraulic characteristics of bifurcated channel under bankfull discharge have great impact on the sediment deposition and erosion, the diversion ratio and sediment distribution ratio, as well as the transport of pollutants. In this research, generalized fixed-bed experiment was performed on Daijiazhou segment of the middle stream of Yangtze River as a case study. The variations in hydrodynamic characteristics along curved bifurcated channel under different characteristic flows were analyzed, and the abrupt changes of hydraulic characteristics in different regions of the bifurcated channel under bankfull discharge were examined as well. Results implied that in flow diversion region, the longitudinal slope gradient increased under small discharge, while declined under big discharge; and vice versa in the convex bank; but in concave bank, the longitudinal slope gradient increased along the flow direction. In the adjacent of bankfull discharge, the longitudinal slope gradient in flow diversion region experienced a maximum value, whereas the amplitude of slope gradient undergone a minimum value. In addition, the locations of mainstream line and maximum bed shear stress transferred from the concave bank to the convex bank.
WATER RESOURCES AND ENVIRONMENT
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  A Holistic Method of Riverine Connectivity Assessment

  CHEN Ang, WU Miao, ZHOU Xiao-guo, ZHONG Zhou-wen, GAN Fang-mao, FU Xing-wei, HUI Er-qing

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 21-27. https://doi.org/10.11988/ckyyb.20181123

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  Guaranteeing riverine connectivity is of pivotal significance to protecting and restoring ecological system. In-depth research on the theory and methodology of assessing riverine connectivity is in urgent need to promote the linking among rivers, lakes and reservoirs. In this paper, a comprehensive assessment method for riverine connectivity is proposed. Five indicators including degree of fragmentation, coefficient of reservoir capacity regulation, water consumption rate, road network density, and nightlight intensity in urban areas are chosen to represent the connectivity in longitude, vertical, horizontal and temporal scales. On the basis of analyzing threshold value and weight of the indicators, the connectivity index is put forward to represent holistic connectivity. The assessment standard is also discussed to provide reference for river connectivity restoration. This research result will provide new ideas for the practice of river ecosystem protection.
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  Coupling Correlation Measure and Prospect Forecast of Water Resources Environment and Economic Development in Jinan

  LIU Yi, ZHANG Zheng-xian, ZHANG Feng-xian, LIU Bo

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 28-33. https://doi.org/10.11988/ckyyb.20181277

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  The coupling mechanism between water resources environment and economic growth in Jinan City is studied quantitatively and qualitatively by integrating coupling correlation degree model with environmental Kuznets curve (EKC). Meanwhile, the development prospect between the two is predicted using elasticity forecast method. Result illustrates that coupling relationship exists between water resources environment and economic growth in Jinan from 2005 to 2017. Under current conditions, the coupling between domestic water use as well as sewage and economic growth is higher than that between industry water use and economic growth. In addition, the concepts of potential risk control indicators and key monitoring indicators are introduced according to EKC trends and forecast results. Potential risk control indicators include domestic COD and industrial NH₃-N, while key monitoring indicators are domestic NH₃-N, wastewater, as well as industrial and domestic water use. The results are expected to provide basis for promoting the coordinated development between regional economy and water resources environment in Jinan.
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  Simulation of Urban Lake Cooling Effect with Varying Lake Factors: Case Study of Hunan Martyrs Park Lake

  LONG Li-juan, CHEN Cun-you, HU Xi-jun, HU Ying-xuan

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 34-40. https://doi.org/10.11988/ckyyb.20180933

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  Urban lake plays an important role in reducing the urban heat island effect. With the lake in the martyr park of Hunan Province as study object, we probed into the influences of lake area and lake shape index (perimeter-to-area ratio) on the lake cooling effect through field measurement and CFD (Computational Fluid Dynamics) simulation. Results show that: 1) Lake area is the major factor that affects the cooling effect of lake. The smaller lake area, the weaker the cooling effect. In the control area (area for comparison with no lake), the mean temperature increases by 1.8 ℃ in general, and the green land in lake increases by 4.1 ℃ to the maximum. 2) Lake shape index has a weak influence on the cooling effect of lake which increases slightly with the increase of shape index. 3) Under the condition that lake area remains unchanged, an excessive shape index will greatly affect the integrity of the water body, thus weakening the cooling effect.
ENGINEERING SAFETY AND DISASTER PREVENTION
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  Cloud Model of Evaluating Debris Flow Susceptibility Based on Combinatorial Weighting of Game Theory

  WANG Nian-qin, ZHANG Shuai, LIU Peng

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 41-47. https://doi.org/10.11988/ckyyb.20180136

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  Debris flow is a common geological disaster in the mountainous area of west China leading to huge loss of people’s property and life and devastating ecology and geological environment. Evaluating the susceptibility of debris flow accurately is of crucial importance to disaster prevention and mitigation. In this paper, a cloud model of evaluating the susceptibility of debris flow is built based on the game theory. The susceptibility of debris flow is classified into four levels: not susceptible (level Ⅰ), lowly susceptible (level Ⅱ), moderately susceptible (level Ⅲ), and highly susceptible (level Ⅳ). Qualitative indices are determined as slope gradient of gullies (index X₁), longitudinal gradient of gully bed (index X₂), vegetation coverage (index X₃), solid material source storage per unit area (index X₄), catchment area (index X₅), and rainfall in wet season (index X₆). The criteria of rating these indices and the characteristic quantities of the corresponding cloud models are proposed. Moreover, the subjective weights and objective weights of the evaluation indices are calculated using hierarchy analytical method and entropy method respectively, and the combinatorial subjective and objective weights are given in the light of the game theory. The effectiveness of the proposed model is verified by five debris flow examples in the west Qinling Mountain area. The evaluation result is consistent with the actual situation in general. The model is further applied to evaluating the susceptibility of debris gully in Xi’an, and the result suggests that the debris flow is moderately susceptible (level Ⅲ).
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  Rainfall Thresholds of Rainfall-triggered Landslides in Cili County,Hunan Province

  LIN Wei, LI Yuan-yao, XU Yong, LIAN Zhi-peng, CAO Ying, SHENG Yi-fan

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 48-54. https://doi.org/10.11988/ckyyb.20181125

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  The key to hazard control and reduction for rainfall-triggered landslide is to identify the warning threshold scientifically. With Wuling mountain area as an example, historical landslide data and rainfall data from 1987 to 2011 were analyzed statistically using SPSS to reveal the relevance between rainfall and landslide event. Rainfall-triggered landslide in this region was mainly affected by the accumulated rainfall in the first three days of rainfall, and the effective coefficient of early-stage rainfall was only 0.6. Subsequently, based on the empirical threshold analysis model, the macroscopic I-D(intensity-duration) rainfall threshold curve for staged early-warning was established and verified through known rainfall landslide events. In view of the differences in scale, thickness, and slope gradient of landslides in the region, the I-D threshold curves corresponding to different geological conditions were built. Results unveiled that the rainfall threshold was evidently positively correlated with the scale and thickness of landslide, whereas slope gradient had an apparent susceptible interval (25° to 35°) where rainfall threshold reached the minimum. The conclusion offers reference for the forecast of rainfall landslide in Wuling mountain area and related areas.
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  Distribution Characteristics of Geological Hazards in Southwestern Shallow Hill Based on AHP-Logistic Entropy Combined Weight Model:A Case Study of Neijiang City

  CHEN Chao-liang, PENG Shu-hong, QIAN Jing, HU Zeng-yun, ZHANG Wen-jun, XU Kai-bin

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 55-61. https://doi.org/10.11988/ckyyb.20181136

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  In an attempt to probe into the distribution of geological disasters in southwest China where geological disasters happen frequently, we built an index system for assessing the eco-geological environment of Neijiang City as a case study based on remotely sensed images and geographical monitoring data. The index system includes factors of natural geography, ecological condition, and fundamental geology. Furthermore, the subjective weight and objective weight of each index were determined by analytic hierarchy process (AHP) and dichotomous Logistic regression model; and the combinatorial weight was synthesized according to minimum relative information entropy principle. The evaluation model of geological hazard was hence established with the support of GIS to evaluate the risk of geological disasters in Neijiang City. The distribution characteristics and laws of geological disaster was acquired by spatial analysis using higher weight coefficients and the corresponding historical geological disaster points. Results show that the low mountainous area in the west of Neijiang, which accounts for 28.93% of the total area, is highly susceptible to geological disasters. Altitude and slope gradient are major influential factors that induce geological disasters; geological disasters are highly prone to occur in high-altitude and steep-slope areas on both sides of highway, whereas in the adjacent of quiet tectonic line the geological formation is relatively stable.
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  Degradation Law of Lateral Bearing Behavior of Corroded Reinforced Concrete Square Piles

  XU Qiu-hong, SHI Dan-da, SHAO Wei

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 62-67. https://doi.org/10.11988/ckyyb.20181158

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  To study the degradation law of lateral bearing behavior of corroded RC (reinforced concrete) square piles, the governing model of chloride diffusion into RC square pile was established based on Fick’s second law. According to the initial and boundary conditions, the analytical solution of chloride diffusion equation was presented. Based on Faraday’s law, the corrosion depth and the time for corrosion-induced cover cracking in RC square pile were estimated. On this basis, the degradation coefficient of the bending stiffness of the RC square pile was introduced, and the lateral bearing behavior of corroded RC square piles exposed to marine environment was further analyzed. The analysis results illustrated that the chloride-induced reinforcement corrosion had a significant influence on the behavior of laterally loaded RC square piles exposed to marine environments. The bending stiffness of the RC square pile decreased obviously with the increase of the exposed time and deterioration of exposure condition; while the maximum negative shear force, the lateral deflection and the bending moment increased with the increase of the exposed time. Given the same load, the exposed time posed a more obvious impact on the horizontal displacement of pile than on shear force and bending moment. The research findings offer reference for the design of RC pile foundation subjected to marine environment.
AGRICULTURAL WATER CONSERVANCY
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  Influence of Exogenous Humic Acid on Heavy Metal Cd Activity in Clayey Farmland Soil

  ZHANG Di-meng, HU Yan-ping, WANG Zhen-hua, LI Qing-yun, LI Guan-ya

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 68-71. https://doi.org/10.11988/ckyyb.20181110

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  The effects of two different extrogenous humic acids on the activity of Cd in clayey farmland were examined by measuring the content of total Cd, DTPA-Cd and MgCl₂-Cd after leaching treatment. After two humic acid treatments, the total content of Cd content in the soil remained unchanged in general, the content of DTPA-Cd decreased from 0.421 mg/kg to 0.313 mg/kg, and the content of MgCl₂-Cd declined from 0.2 mg/kg to 0.169 mg/kg. When leaching time increased from 1 day to 5 days, the total content of Cd also remained unchanged overall, DTPA-Cd decreased from 0.325 mg/kg to 0.265 mg/kg, and MgCl₂-Cd reduced from 0.196 mg/kg to 0.165 mg/kg. In conclusion, both the exogenous humic acids could remove Cd in the soil of clayey farmland.
ROCK SOIL ENGINEERING
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  Appraisal on Selection of Disturbance Factor for Engineered Slopes by Hoek-Brown Criterion 2018 Edition

  CHEN Zu-yu, ZHOU Jia-wei, CAI Yun-peng, SUN Ping, DENG Cheng-jin

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 72-80. https://doi.org/10.11988/ckyyb.20191279

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  The Hoek-Brown failure criterion for determination of non-linear shear strength of rock mass has been under constant upgrading during the past two decades. The latest 2018 version summarizes the main issues on utilizations and key factors of this system. One major concern of using this system comes from the appropriate selection of the disturbance factor D that ranges from 0 to 1, covering the applications in tunneling and slope engineering with conditions varying from well controlled to uncontrolled excavations. This paper focuses on the values of D that best fits the application in hydro-slopes, normally excavated under controlled blasting works. The main approaches include the comparisons between GSI-1995 and GSI-2018 versions. The former has been suggested in China’s hydro-slope design standard. A simple test example was investigated by varying its geometry and physical parameters, with the finding that D ranges from 0.78 to 0.88 as the two versions offer the same factor of safety. Three engineered slopes of hydropower projects that originally adopted GSI-1995 version were investigated. The calibration work that equivalents the two versions suggests that D ranges from 0.72 to 0.85. The authors then suggest adopting D ranging from 0.7 to 0.9 for hydro-slope design.
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  Application of Pressure Transient Analysis Method in Mini-Frac Test

  XU Bin, LIU Ru-ming, CHEN Zi-yang, REN Qiang

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 81-86. https://doi.org/10.11988/ckyyb.20181013

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  Mini-Frac test is the most reliable in-situ testing protocol for measuring the in-situ stress condition at deep. A critical part of a Mini-Frac testing analysis is the analyzing of the fracture closure pressure which, in theory, equals to the minimum in-situ stress. The foundation of all Mini-Frac analysis is the one-dimensional fluid flow model considering a vertical well intersected by a vertical fracture with finite or infinite fracture conductivity, which naturally lead to the concept of pressure transient analysis (PTA). Although the PTA method has been widely used in the oil/gas industry for more than three decades, the application of PTA in the Mini-Frac test in rock mechanics engineering is new and few publications are available. Based on literature review, we introduce the concept of pressure transient analysis and its application in the Mini-Frac stress measurements. With the support of the partial differential equation (PDE) simulating the process of pressure falloff stage during a Mini-Frac test, we present different flow regimes describing open, closing, and closed fracture systems. These flow regimes are manifested on the pressure derivative plots which are used to identify the fracture closure pressure. In the last section of this paper, we share a real Mini-Frac test example and discuss the analysis results and compare it with other analysis methods.
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  Correction of 3D Modelling Errors for Tunnel’s Working Face Using Sirovision

  ZHOU Shen, HU Chao, LI Li-ping, WANG Xiang-guo, DONG Chen-yang, XU Xiao-bin, LIU Hong-liang

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 87-92. https://doi.org/10.11988/ckyyb.20180783

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  In view of the low efficiency, high risk factor, and poor accuracy of traditional methods in measuring the structural information of rock mass, a method for measuring the information of tunnel rock mass based on Sirovision was studied. Through quantitative analysis and comparative experiments, the environment factors and work process of measurement were analyzed, and the sources in 3D modeling errors of tunnel surrounding rock under complex tunnel environment were studied. Moreover, corresponding correction methods, such as determining control positions, marking measurement points, and matching photogrammetric points were proposed. The proposed method was applied to the information acquisition and stability analysis of the tunnel rock mass in Yaojiayu tunnel of Binzhou-Laiwu high-speed project, and good results were obtained. The proposed method could be taken as reference for researchers when applying photogrammetry technology to tunnel’s safe construction and support parameter optimization.
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  Macroscopic and Microscopic Experimental Research on One-dimensional Consolidation Compressibility of Marshy-Lacustrine Clay

  ZHU Nan, LIU Chun-yuan, ZHAO Xian-hui, WANG Wen-jing

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 93-99. https://doi.org/10.11988/ckyyb.20181023

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  The physico-mechanical properties and compressibility of marshy-Lacustrine clay, a special regional soft soil, differ from those of other soft soils markedly. We performed oedometer tests to investigate the consolidated compressibility and mechanism of marshy-Lacustrine clay, and analyzed quantitatively and qualitatively the change of microstructure characteristics by extracting the microstructural parameters under different pressures using scanning electron microscopy and computer image processing. Results demonstrated that due to apparent structural strength, the compressibility of undisturbed marshy-Lacustrine clay was significantly smaller than that of reconstituted soil. Such structural strength perished gradually when the consolidation pressure exceeded the structural yield stress. Moreover, the change laws of the microstructural parameters varied and displayed a form of two broken lines when the consolidation pressure was around the structural yield stress, and also at this time the dynamic restructuring of the soil is the fundamental cause of the change of compressibility of marshy-Lacustrine clay. During consolidation compression, the morphological characteristics and directionalities of pores changed markedly, while the morphological characteristics of particles changed slightly but the directionalities of particles changed remarkably. The particles and pores affect the compressibility of soil in different ways.
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  Experimental Study on Flexural Bearing Capacity of Micropiles

  CHEN Zai-qian, SHUAI Shi-jie, PU Shu-tao, ZHANG Li-hua, RAO Jun-ying, LIU Deng-kai, XIE Cai-jin

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 100-105. https://doi.org/10.11988/ckyyb.20181056

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  Micropile is superior to conventional retaining structures in the emergency treatment of landslide, embankment slope, or foundation pit with poor stability. Since the bearing capacity and failure characteristics of different micropiles vary, we improved the yas-2000 compression testing machine and applied it to measuring the flexural bearing capacity of three different micropiles: reinforced concrete pile, steel pipe concrete filled rebar pile, and steel pipe concrete filled I-beam pile. Results unveiled that the whole process of force acting on reinforced concrete pile can be divided according to three phases, namely, uncracked phase, cracked phase, and destruction phase. The stress process of steel pipe concrete filled rebar pile, and steel pipe concrete filled I-beam pile can be divided into four phases, compaction phase, elastic phase, elasto-plastic phase, and reinforcement phase. In addition, comparison of the load-displacement curves of these three micropiles revealed that given the same diameter, steel pipe concrete filled I-beam pile has the largest flexural bearing capacity with the ultimate bending moment reaching 209.21 kN·m.
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  DEM-based Analysis of Movement and Accumulation Characteristics of Turning-type Landslide

  YANG Hai-long, FAN Xiao-yi, PEI Xiang-jun

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 106-111. https://doi.org/10.11988/ckyyb.20180788

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  Understandings on the movement characteristics of turning-type landslide in Shanyang county, Shaanxi Province, are obtained through discrete element analysis. The notable difference of movement velocity in the front edge of landslide lies in the differences in motion space, energy transfer, and deflection and blocking effect at each monitoring point in the leading edge of the landslide. The rock and soil mass in the middle of the landslide, as the major medium of energy transfer between the leading edge and the trailing edge, experienced multiple accelerations. The monitoring points in the trailing edge mainly experienced two stages, namely, acceleration and deceleration. Affected by the turning force, Shanyang landslide is a short-range landslide with high velocity according to the movement speed and horizontal distance, and the thickness of the accumulation body increased at first and then decreased along the motion direction.
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  A Simplified Calculation Method for Shear Strength of Tap Root-Soil Composite

  MA Qiang, LI Zhi, XIAO Heng-lin, WAN Juan

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 112-118. https://doi.org/10.11988/ckyyb.20181184

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  A simplified formula for calculating the shear strength of tap root-soil composite is derived based on the stress analysis of tap root-soil composite in consideration of the failure mode of root system. The calculation results are compared with field measured values. Moreover, the influences of reduction coefficient, root weight, and plant species on the strength of the root-soil composite are also investigated. Results imply that the cohesion of the composite is an exponential function of soil depth. When normal stress is constant, the shear strength of the composite increases with the augment of reduction coefficient. When the reduction coefficient is in the range of 0.84-0.86, the result is closer to the measured value. In addition, the shear strength of the composite increases with the increase of root weight, and then decreases gradually. A optimum root weight is found to make sure a maximum shear strength. With the normal stress increasing, the shear strength of the composite is also increasing. The relative error between calculated shear strength and measured strength is kept within 10%.
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  Nonlinear Characteristics and Expression of Viscosity Coefficient of Coastal Soft Clay

  LIU Su-mei, HU Hui-ying, LI Chun-guang, WANG Li

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 119-125. https://doi.org/10.11988/ckyyb.20181066

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  Analysis on triaxial creep test data of coastal soft soil reveals that viscosity coefficient is not only related to time, but also to the deviatoric pressure and confining pressure of soil. The relation between strain rate and time is of perfect double logarithmic linear characteristics. Hence, viscosity coefficient is a power function of time. Sensitivity analysis of deviatoric pressure unveils that viscosity coefficient is linearly dependent on deviatoric pressure and exponentially on confining pressure. Last but not the least, the nonlinear relations between viscosity coefficient with time, deviatoric stress and confining pressure are established and applied to the direct shear creep test of coastal soft soil. The proposed expression is applicable to describe the variation of viscosity coefficient of soft soil with apparent nonlinear characteristics and high stress level along with time and stress. In addition, factors affecting the relevant parameters are also put forward. The research findings lay a foundation for building the nonlinear rheological model coastal soft soil
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  Size Effect on Brazilian Splitting Tensile Strength of Sandstone

  XU Kuai-le, LIU Cong-ying, NI Xing, ZHU Yu, WAN Liang-peng, DENG Hua-feng

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 126-129. https://doi.org/10.11988/ckyyb.20180858

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  Size effect is an unavoidable problem in rock mechanics experiment, and is directly related to the rationality of rock mechanics parameters. In previous studies on the size effect of rock splitting tensile strength, the influence of thickness-to-diameter ratio of rock specimen was mostly considered rather than the influence of rock sample diameter. In view of this, we performed Brazilian splitting tensile strength tests on specimens of five different diameters (25, 30, 50, 100, 150 mm). Results unveiled that: 1) at given thickness-to-diameter ratio, the tensile strength of rock sample declined from being sharply towards gently as the diameter augmented from 25 mm to 150 mm. When the diameter exceeded 50 mm, tensile strength tended to be stable. Such variation trend can be well fitted by exponential function. 2) The size effect of splitting tensile strength of rock is not only related to the thickness-to-diameter ratio, but also related to the diameter of rock specimen. According to previous research experience, we suggest that the thickness-to-diameter ratio around 0.3, and diameter more than 50 mm, in which case the size effect on splitting tensile strength can be well eliminated.
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  Initial Yield Function about the Moistening Deformation of Undisturbed Loess

  ZHANG Li-xin, DING Ye, REN Yong-zhong

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 130-134. https://doi.org/10.11988/ckyyb.20181029

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  The stress-strain relation of undisturbed loess with varied initial moisture content was examined via conventional triaxial shear test and isotropic compression test. Shear test revealed that the critical state lines of undisturbed loess approximated to be straight lines which shifted along the q axis up and down horizontally with the variation of moisture content but do not pass through the coordinate origin of the p-q plane. Triaxial compression test demonstrated that the e-lnp curve of undisturbed loess was a broken line rather than a straight line, and the spherical stress at the fold point declined with the increase of initial moisture content. Under the hypothesis of ellipse yield locus, the initial yield function of undisturbed loess was acquired, according to which the initial yield stress and initial moisture content in different stress paths can be predicted. The present research lays a foundation for establishing the constitutive model of undisturbed loess during the process of moistening deformation.
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  Influence of Dry-Wet Cycles on Shear Properties of Xigeda Soil

  WANG Ying

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 135-140. https://doi.org/10.11988/ckyyb.20180847

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  The influence of cyclic drying and wetting on shear parameters (cohesion and internal friction angle) must be identified in calculating the earth pressure of filling by Xigeda soil involved with water. The shear stress-displacement curve of Xigeda soil was acquired from consolidated drained shear test under cyclic drying and wetting. Soil specimens were humidified by vacuum saturation and dehumidified in natural status to simulate the drying-wetting progress. The variations of peak shear stress, cohesion and internal friction angle with the number of drying-wetting cycles were analyzed. Furthermore, the relationship between macroscopic and microcosmic parameters was discussed by the parallel contact model, and the differences between bond and friction characteristics among micro particles were revealed. Test results showed that the wetting action reduced the cohesion and internal friction angle of the soil. As the number of drying-wetting cycles increased, the stress-displacement curves displayed strain hardening features to strain softening features, and peak strength, cohesion and internal friction angle all decreased and tended to be stable. In the first three cycles, cohesion decreased by 55.42%, while from the second to the forth cycle, internal friction angle decreased by 11.04%. The effect of drying-wetting cycle on cohesion was apparently greater than that on internal friction, and the deterioration effect on internal friction angle delayed. We recommend to weaken the influence of drying-wetting cycles on the mechanical properties of Xigeda soil by means from the aspect of the bonding effect among micro particles.
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  Experimental Study on Mechanical Properties of Rock Containing Natural Micro-fractures

  NIU Liang, MU Rui, CHEN Jun

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 141-146. https://doi.org/10.11988/ckyyb.20181166

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  Uniaxial compression test, splitting test and SEM scanning test were performed to investigate the splitting mechanical properties and microstructure of rock containing natural microfractures. The failure modes and tensile strength of rock containing natural microfractures undergone uniaxial compression test and splitting test were analysed; the microstructure of the broken part of rock specimens of splitting failure mode was examined as well. In uniaxial compression test, the failure modes of rock specimens containing natural microfractures were mainly tension failure, shear failure along natural fracture surface, and tension-shear composite failure; the dip angle of natural microfracture had a remarkable influence on the tensile strength of rock which increased with the increase of dip angle. On the other hand, after splitting failure, the splitting mechanical properties were largely determined by the microstructure of natural microfractures which can be classified as three types, namely, root structure, fog area structure, and step structure, among which root structure had the most inferior mechanical properties whereas step structure was of good mechanical properties.
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  Stability Analysis of Slurry Trench of Irregular Shaped Diaphragm Wall in Cohesive/Frictional Soils

  ZHOU Yang, LIU Wei, SHI Pei-xin, ZHU Ning, HOU Guan-fei

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 147-152. https://doi.org/10.11988/ckyyb.20180978

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  The L-shaped diaphragm wall is broadly used to form an enclosed retaining structure underground. Due to the complicated stress condition during trenching construction, the stability of L-shaped trench is lower than that of regular rectangular trench. In this paper the instability mechanism of irregular-shaped diaphragm wall during the excavation of L-shaped slurry trench is revealed based on upper bound analysis. A 3D kinematically admissible mechanism defining the failure of the L-shaped trench is constructed. The safety factor of the trench and corresponding failure pattern are obtained through upper bound analysis. Moreover, the influences of trench geometries and soil properties on the trench stability are discussed through parameter analysis. The calculation result of a case study is consistent with the field ultrasonic inspection result.
HYDRAULIC STRUCTURE AND MATERIAL
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  Long-term Drying Shrinkage Performance of Steel Slag Cement Mortar under Unconstrained Multi-condition

  WANG Xiu-hong, WANG Jun, BAI Jian-fei, JIN Qiang, ZHU Lin, YUAN Zhen

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 153-158. https://doi.org/10.11988/ckyyb.20181053

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  Industrial steel slag can be used as an additive in concrete as it contains such minerals as C₂S and C₃S which have similar gelling properties with cement clinker. Nevertheless, excessive dosage of industrial steel slag would result in inferior stability because it also contains f-CaO and f-MgO. To better utilize fine aggregate of steel slag in cement mortar, we performed drying shrinkage test to investigate the influence of steel slag on the long-term drying shrinkage performance of cement mortar at different curing ages under different curing conditions. Test results demonstrated that under standard curing condition, the drying shrinkage rate of cement mortar reached the lowest when added with 60% single steel slag powder, or 70% single steel slag sand, or 20% powder mixed with 40% sand, or 30% powder mixed with 60% sand; under constant temperature curing condition, the long-term dry shrinkage value of cement mortar was the lowest when 35% of steel slag powder was mixed with 40% steel slag sand.
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  Tensile Performance Test on Cement-stabilized Recycled Aggregate as Pavement Base

  CHEN Feng, TONG Sheng-hao

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 159-163. https://doi.org/10.11988/ckyyb.20181089

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  As the base of pavement, cement-stabilized aggregate base mixture is affected by temperature difference between day and night which brings about swell-shrink stress inside the material. Meanwhile, cement-stabilized aggregate base mixture, as the major load-bearing layer of pavement, is subjected to an external shear stress under non-uniform stress. Splitting-tensile performance is a crucial indicator. In this paper, splitting tensile test and splitting tensile rebound test were conducted on cement stabilized clastic rock and cement stabilized recycled aggregate respectively. Test results suggest that the strength and modulus of elasticity both increased power-exponentially with age. The splitting-tensile performance of cement stabilized recycled aggregate is slightly lower than that of cement stabilized clastic rock; properly increasing the amount of cement could fill the gap. In addition, a good linear relationship is found between the strength and the modulus of elasticity via numerical fitting.
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  Simulation of Viscoelastic Artificial Boundary Based on Thin Layer Element

  HOU Heng, YANG Jie, CHENG Lin, LÜ Gao, MA Chun-hui

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 164-169. https://doi.org/10.11988/ckyyb.20181068

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  In practical application, viscoelastic artificial boundary is featured with such defects as long preprocessing and difficulty of implementation. In view of this, a method of simulating viscoelastic artificial boundary based on thin layer element is proposed. Equivalent viscoelastic boundary element composing thin layer is constructed in light of the principle of element matrix equivalence. By setting the parameter attributes of the equivalent viscoelastic boundary element in finite element software MSC MARC, the artificial viscoelastic boundary can be simulated. A computation example of three-dimensional uniform elastic semi-space and a practical engineering example of concrete gravity dam demonstrate that the calculated results obtained by using the equivalent viscoelastic boundary element are very close to the theoretical solution and the calculated values based on the viscoelastic artificial boundary, with the relative error smaller than 1%. Therefore, the simulated viscoelastic artificial boundary using thin-layer elements has sufficient accuracy and is easy to apply, thus providing a simple and accurate method for seismic analysis in practical engineering.
INSTRUMENTATION DEVELOPMENT AND TESTING TECHNIQUES
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  Engineering Applications of Fusion of 3D Laser Scanning and Infrared Detection Technology

  SUN Bao-yan, CHEN Wen

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 170-173. https://doi.org/10.11988/ckyyb.20181192

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  The 2D image obtained by traditional infrared thermal imager lacks target position and the data is chaotic in the detection of thermal defects of building wall. In view of this, a method by fusion of image information and point-cloud model is presented in this paper. This method obtains a 3D building model with target information through infrared image processing, histogram area calculating, edge contour extracting and model fusing. The mosaic error of the obtained model is also analyzed using the identification points. Research and experimental results demonstrate the feasibility of the present method and the high precision of the splicing model. The position coordination and area of thermal defects can be acquired directly by the integrated 3D building model to guide the repair work. The research finding is of guiding significance and application value for integrated information management and intelligent building detection.
INFORMATION TECHNOLOGY APPLICATION
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  Network Monitoring and Alarming System for Grouting Pressure Based on SPC Theory

  LI Bin, GUO Liang, LIU Shuang-hua, ZHAN Cheng-yuan, JIA Bao-liang

  Journal of Changjiang River Scientific Research Institute. 2020, 37(2): 174-178. https://doi.org/10.11988/ckyyb.20181197

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  In grouting pressure control, traditional alarming based on pressure threshold is sometimes erroneous and delayed. In view of this, a network monitoring alarming system for grouting pressure is developed based on the theory of Statistical Process Control (SPC). Fengning pumped storage power plant (stage I) in Hebei Province with a large amount of toe plate curtain grouting is taken as a case study. The system identifies the position of sampling points and the pressure change trend by monitoring the grouting pressure value through sampling and generates pressure control diagrams based on SPC. Moreover, different pressure judgment criteria for different stages of grouting are set. Hence, the monitoring, alarming, and prediction of grouting pressure can be accomplished. Compared with traditional pressure threshold alarming, the present system reduced the time-consumption of alarming by 25% while promotes the alarming efficiency by 8%. By integrating SPC and threshold algorithm, we could identify abnormal information in advance, favorable for grouting management and control.