Journal of Hydroelectric Engineering

水力发电学报

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2018 Vol. 37, No. 2 Published: 2018-02-25

	1	Structural stability of complex tunnel surrounding rock and its control
		ZHANG Dingli, SUN Zhenyu
		DOI: 10.11660/slfdxb.20180201
		Stability of tunnel surrounding rock, a core issue in underground tunnel design, has been a hot research field in tunnel engineering, and an accurate assessment of the stability is an important precondition for construction safety under complicated geological conditions. Aiming at this issue, first we conduct laboratory tests of tunnel surrounding rock to examine its behaviors of gradual destruction and reveal its staged development characteristics of instability and failure. Then, through analysis of the instability mechanism, a mechanical model of tunnel surrounding rock instability and a method for calculating the instability thresholds are developed. According to its stable behaviors and instability modes, tunnel surrounding rock is divided into inner and outer layers, and thus a compound surrounding rock structure model can be constructed. This study reveals that its developing stages of instability are essentially a consequence of the outer surrounding rock moving in a mode of grouping, and the characteristics of its structure stability are thus analyzed. For application to complicated and variable ground conditions, a systematic study is carried out focusing on the structure of composite surrounding rock in different stratigraphic conditions, and it shows the "composite arch" effect of the sand surrounding rock and the "beamed arch" structure and "multi-layer arch" effect of layered surrounding rock, together with the stability characteristics of these types of surrounding rock. Finally, a new stability control technology of complicated tunnel surrounding rock is presented in this paper. This study lays a theoretical basis for safety of tunnel construction and design of tunnel support.
		2018 Vol. 37 (2): 1-11 [Abstract] ( 219 ) PDF (1089 KB) ( 539 )

	12	Unconfined compressive strength of synthetic cotton fibers reinforced soil
		LIU Jianlong, HOU Tianshun, LUO Yasheng
		DOI: 10.11660/slfdxb.20180202
		To examine the strength and deformation properties of synthetic cotton fibers reinforced soil, an experiment is conducted to measure its unconfined compressive strength with six different fiber contents (0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3.0% by weight), four different fiber lengths (1.25, 2.50, 3.75 and 5.00 cm), and three different patterns of fiber distribution (random distribution, layered cross distribution and layered one-way distribution). Results show that as both fiber content and fiber length increases, the compressive strength is increased first and then decreased, with a peak strength in the condition of fiber content of 1.0% and fiber length of 2.50 cm. Under this optimum condition, the strength is increased by 24.8% when the reinforcing fibers are added in the pattern of random distribution and decreased by 15.1% when added in layered one-way distribution, while it remains nearly the same if the fibers in layered cross distribution. The stress strain characteristics of the reinforced soil are strain hardening. With both fiber content and fiber length increasing, its average deformation modulus is increased first and then decreased, varying in the range of 0.56 - 1.26 MPa. This experiment demonstrates that the reinforcing fibers will help restraining soil radial displacement and increasing soil strength if certain reasonable and practical means can be used to control their distribution patterns so as to keep them oriented along the local tensile stress.
		2018 Vol. 37 (2): 12-21 [Abstract] ( 153 ) PDF (1343 KB) ( 510 )

	22	Frequency estimation of hydrological samples with zero values
		LI Yunping, SONG Songbai, LI Dandan
		DOI: 10.11660/slfdxb.20180203
		This paper presents a study on frequency analysis method of hydrological samples with zero values, focusing on the derivation of parameter estimation formulas of Gamma distribution for the nonzero values and full series using maximum likelihood method (ML), the principle of maximum entropy (POME), and probability weight moment method (PWM). We also discuss the relationship between nonzero values and full series and the calculation of design values of hydrological samples. Monte-Carlo simulations are conducted to examine the influence of different sample lengths on the design values calculated using different methods of parameter estimation. Applicability of these methods are evaluated through a case study of six monthly precipitation samples observed in Shaanxi, including the effect and calculation error of fitting large sample events. The results indicate that both the principle of maximum entropy and maximum likelihood method have a good fitting effect, forming a theoretical basis for frequency analysis of the hydrological samples with zero values.
		2018 Vol. 37 (2): 22-31 [Abstract] ( 139 ) PDF (419 KB) ( 380 )

	32	Assessing impacts of extreme water and temperature conditions on carbon fluxes in two desert shrublands
		GONG Tingting, LEI Huimin, YANG Dawen, YANG Hanbo, LIU Tingxi, DUAN Limin
		DOI: 10.11660/slfdxb.20180204
		We study the seasonal patterns of carbon fluxes in two desert shrublands of North China , Yulin Station in Shaanxi Province and Tongliao Station in Inner Mongolia Autonomous Region, using the eddy covariance technique, and qualitatively estimate the impact of extreme temperature and water conditions on carbon fluxes. Our findings show that (1) during 2011-2012, the total net ecosystem exchange (NEE) of Yulin and Tongliao were -132.8 and -59.6 gC/m2/yr respectively, indicating that the shrub ecosystem carbon fixation capacity in Yulin was obvious. (2) Extreme water and temperature conditions have significant effects on carbon fluxes, especially extreme water conditions. On an average over the growing period (April-October), the differences of NEE relative to normal conditions at Yulin and Tongliao are 0.51 and 0.26 gC/m2/s in the extreme water condition and 0.17 and 0.20 gC/m2/s in the extreme temperature condition, respectively. (3) In the peak growing period (July-August), the extreme high temperature (above 27 ?C at Yulin and above 29 ?C at Tongliao) effectively inhibits vegetation photosynthesis, decreasing gross primary production (GPP) by 0.37 and 0.53 gC/m2/s respectively, relative to the normal temperature condition.
		2018 Vol. 37 (2): 32-46 [Abstract] ( 163 ) PDF (2655 KB) ( 298 )

	47	Peak-shaving benefit model of cascade hydropower stations based on daily peak modes
		WANG Wei, MEI Yadong, BAO Zhengfeng
		DOI: 10.11660/slfdxb.20180205
		Full use of the peak-shaving capacity of hydropower stations could bring more economic benefit. This paper describes a long-term optimization model that maximizes the peak-shaving benefit expectation based on a scenario reduction technique, the curve of peak-shaving price, and the otherness of daily load curves that reflects peak-shaving demands in different dispatch periods. This model extracts typical daily curves of peak-shaving operation for single-peak, double-peak and monthly-peak modes through simultaneous backward reduction, then simulates the curves of peak-shaving price for the three modes based on the daily curves extracted, and finally generates a peak-shaving price series. Calculations in a case study of the Three Gorges cascade hydropower stations show that the model could reflect the influence of different short-term peak-shaving operation modes on long-term dispatch and improve peak-shaving efficiency significantly, thus helping design long-term dispatch schemes of cascade hydropower stations.
		2018 Vol. 37 (2): 47-58 [Abstract] ( 163 ) PDF (500 KB) ( 385 )

	59	Rolling forecast for reservoir monthly average flows and its uncertainty
		MA Chao, CUI Xiyan
		DOI: 10.11660/slfdxb.20180206
		Reliable reservoir inflow forecast is the basis of long-term reservoir scheduling decision. This paper describes a new method of rolling flow forecast that gradually increases forecast horizon using the artificial neural network to overcome the limitation of traditional medium- and long-term flow forecast models on forecast horizon and their uncertainty in flow forecasting. A Copula function is adopted to construct joint distribution functions for the sequences of prediction errors and realize random simulation of hydrological prediction errors, and thus this method can describe flow forecast uncertainties quantitatively. Calculations of the monthly average flow and the uncertainties for the Three Gorges reservoir in late non-flood season show that our new method is satisfactory and applicable to practical operation of rolling forecast. Copula functions well describe the correlation between prediction relative error sequences, and often produce small deviation of the correlation coefficients, statistics, and empirical distributions of the simulated sequences from those of the observed sequences.
		2018 Vol. 37 (2): 59-67 [Abstract] ( 191 ) PDF (467 KB) ( 354 )

	68	Reservoir operation method based on different ecological risk degrees
		ZHAO Pengxiao, LI Yong, ZHANG Zhiguang, ZHANG Peng, LI Kefeng
		DOI: 10.11660/slfdxb.20180207
		Ecological operation is a measure of environment protection to balance eco-benefit and other benefits. When a conflict exists between these benefits in reservoir operation, ecological risk degree can be chosen as a decision-making basis for the operation. This paper presents an ecological scheduling model that is based on the hydraulic demands of fish spawning habitat under different ecological risks and the constraints of flow depth and velocity at typical downstream cross-sections of the dam. We use this model to evaluate the ecological risk degree of the spawning ground for Cyprinus carpio rubrofuscus Lacepede at the Yuanjiang Qiaotou hydropower station, and compare five typical daily operation schemes. The results show that the risk degree is zero for two schemes and above 0.5 for the other three schemes. And nine optimized schemes are obtained through optimizing these three schemes with three given target risk degrees of 0.14, 0.29 and 0.43. Comparison shows that the optimized schemes require a reduction in actual power generation with the reduction ratio in a range of 16.29% - 36.37%. Thus our model is able to balance power generation benefit and eco-benefit in the design of ecological scheduling schemes of reservoir operation.
		2018 Vol. 37 (2): 68-78 [Abstract] ( 125 ) PDF (552 KB) ( 345 )

	79	Influence of check gates on channel hydraulic response at diversion and its sensitivity
		GAO Xueping, ZHANG Yan, SUN Bowen, YAN Chendan
		DOI: 10.11660/slfdxb.20180208
		Check gates are important devices for regulating canal operation, a key factor of canal hydraulic response. This study investigates the influence of gate regulation on channel hydraulic response to increasing diversion flux, using a case study of the Xiao Canal operation for the east route of South-to-North Water Diversion project. We adopt hydraulic response indicators of water stage drop rate, water stage peak drop, and transition time at the diversion intake, examine the sensitivity of these response indicators to gate regulation, and develop a system of sensitivity indexes applicable to evaluation of the effects of the gate regulating range and gate distance from the intake on all the response indicators. The results show that the hydraulic response is more sensitive to the regulating range than gate distance.
		2018 Vol. 37 (2): 79-87 [Abstract] ( 184 ) PDF (621 KB) ( 367 )

	88	Influence of low atmospheric pressure on trajectory distance of high velocity jet nappes at high altitude
		PANG Bohui, MA Hongqi
		DOI: 10.11660/slfdxb.20180209
		Low atmospheric pressure in the high altitude areas of Western China presents a new challenge to studies of the hydraulics of high speed flow in high dam construction. The trajectory distance of high speed jet nappes is a key technical parameter for safety design of plunge pools and bank slopes. This paper examines the influence of atmospheric pressure on the nappe trajectory distance using CFD analysis and develops an analytical formula for calculation of the distance under the condition of low atmospheric pressure in high altitude areas. The results show that lower ambient pressure leads to a farther nappe trajectory and the trajectory distance increases roughly by 1.5% when the ambient pressure drops by 10 kPa. Thus, particular attention should be paid to this ambient pressure factor when a relative short plunge pool must be adopted in valley areas to avoid safety risks of plunge pool and bank slope owing to the error in estimation of the nappe trajectories.
		2018 Vol. 37 (2): 88-95 [Abstract] ( 125 ) PDF (759 KB) ( 321 )

	96	Application of efficient high-resolution hydrodynamic model to simulations of flood propagation
		HOU Jingming, LI Guiyi, LI Guodong, LIANG Qiuhua, ZHI Zaixing
		DOI: 10.11660/slfdxb.20180210
		To improve the accuracy, numerical stability and computational efficiency of the existing 2D numerical models of flood propagation and inundation, this paper presents a full hydrodynamic model based on the GPU acceleration techniques (GAST). The model is applied to reproduce a flood event with a return period of 100 years that occurred in Morpeth town, UK. Two grid resolutions of 5 m and 2 m are used in the model and the MIKE21 FM model to investigate different inundation patterns. It is found that the GAST model can achieve an error range of only 0.96% - 4.36% in its calculations of the inundated area and its run-time is 2.17 h and 9.00 h for the 5m and 2m resolutions respectively. It improves computational accuracy and efficiency by 1.07 - 19.55 times and 3.40 - 11.78 times respectively relative to the MIKE21 FM. And this superiority becomes more prominent as the number of grids increases. Thus the GAST model is an ideal tool for modelling flood propagation and inundation.
		2018 Vol. 37 (2): 96-107 [Abstract] ( 174 ) PDF (7336 KB) ( 215 )

	108	Mathematical functions for generating slip surfaces of slopes
		JIE Yuxin, LIU Zhankui, GUO Zhenghao
		DOI: 10.11660/slfdxb.20180211
		In slope stability analysis, the efficiency of searching a critical slip surface increases as the degree of freedom of the solution space decreases, but the narrowed solution space may not be able to cover all the potentially true slip surfaces. In contrast, an increase in the degree of freedom by adding new vertexes of the surface curve can expand the solution space but lower searching efficiency, also undesirable for finding the true solution. Therefore, how to generate slip surfaces is a key question in slope stability analysis. Based on reviewing the traditional methods, this paper presents a new measure for generation of slip surfaces using polar coordinates, a logistic function, and parametric equations. And a comprehensive function for slip surfaces is constructed to simplify slip surface fitting. This measure converts the geometric problem of slip surface generation to a problem of determining the parameters of a known function. Thus it would help reduce the degrees of freedom of the slip surface spaces and narrow the searching ranges of the parameters.
		2018 Vol. 37 (2): 108-120 [Abstract] ( 186 ) PDF (1657 KB) ( 420 )