水力发电学报
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2019 Vol. 38, No. 3
Published: 2019-03-25
 
     
1 Drift velocity of non-uniform suspended sediment
JIA Baozhen, ZHONG Deyu
DOI: 10.11660/slfdxb.20190301
In natural rivers, suspended sediment is generally non-uniform in grain sizes, and the non-uniformity is a major factor in sediment transport and fluvial processes. However, previous studies on non-uniform sediment transport lack attention on the interactions between different grain sizes, and the non-uniformity effect on sediment suspension remains unclear. To elucidate this effect, this paper presents a constitutive equation for the drift velocity of non-uniform suspended sediment. First, applying the two-phase flow theory, we develop basic governing equations of flows and non-uniform sediment transport, focusing on the particle-particle interactions between sediment groups of different grain sizes, and derive two-phase mixture equations for non-uniform sediment-laden flows that can be used to save complicated calculation of interphase interactions. Then, drift velocity is introduced for closure of the two-phase mixture equations, and its constitutive equation is developed to describe the fact that the suspension of non-uniform sediment is attributed to influences imposed by flow turbulence, sediment particles themselves, and more importantly, interaction between particles in different grain sizes. This fact distinguishes the non-uniform sediment transport from the uniform one. Finally, we construct transport equations for non-uniform sediment using this constitutive equation, and obtain vertical concentration profiles for each grain size of the mixture. Comparison of these profiles with measurements shows a good agreement, and we demonstrate the difference from the uniform sediment cases through comparing the profiles to those calculated using Rouse formula. Result shows that when the concentration is higher and the disparity in grain sizes wider, the difference in the vertical profiles between the uniform and non-uniform methods becomes more distinct, and particle-particle interactions play a more important part in sediment suspension. The constitutive equation of drift velocity provides a theoretical way to elucidate the essence and effect of particle-particle interactions on suspension of non-uniform sediment.
2019 Vol. 38 (3): 1-11 [Abstract] ( 247 ) PDF (584 KB)  ( 671 )
12 Classification system of water pollution emergencies in South-to-North Water Transfer Project
LONG Yan, LEI Xiaohui, YANG Yilin, LI Youming
DOI: 10.11660/slfdxb.20190302
The Middle Route of South-to-North Water Transfer Project (MRP) is a large-scale project benefiting the whole nation, and also a key measure of China's future energy development strategy. This paper describes a classification and grading system of water pollution emergencies in MRP based on a driving-pressure-state-impact-responses (DPSIR) framework. First, we construct an evaluation index system using 16 indicators selected to reflect the driving force, pressure, state, influence and response of different regions, and divide them into a static system and a dynamic system by the characteristics of the indicators. Then, their values are specified through a procedure of standardized assignment that considers the overall conditions and requirements of MRP, and the risk level of water pollution emergencies is determined using an analytical hierarchy procedure and a coordinated social development model. Finally, a classification system is described and verified using a case study of the canal bridge S237.
2019 Vol. 38 (3): 12-22 [Abstract] ( 212 ) PDF (548 KB)  ( 470 )
23 Numerical study of wave effects on changes in offshore morphology during storm surges
XU Ludi, HE Zhiguo, PAN Jiajia, HU Peng
DOI: 10.11660/slfdxb.20190303
A two-dimensional numerical model is developed for investigating the effects of waves on sediment transport and bed morphology dynamics under different storm surge conditions. This work is based on an existing shallow water model coupling interactions between the flow, sediment transport, and bed changes. The SWAN model is adopted to simulate wave action, and its simulations of wave radiation stress are coupled into an existing sediment-flow model. Changes in the morphology of an idealized coast in different storm surge conditions are examined and compared. Results show that the wave effect decreases with the raising storm tide level. When the surge is weak, asymmetrical shoals are formed upstream and downstream of the tide inlet and a scour hole is formed at the entrance; at a high surge level, the asymmetry is weak, and the difference in morphological changes calculated with and without the wave effect is roughly 5% at the ratio of water depth to wavelength less than 0.15. Calculating the wave effects could double computational cost. This study also suggests that coupling waves and flows is important for modeling low storm surge tides.
2019 Vol. 38 (3): 23-31 [Abstract] ( 316 ) PDF (1123 KB)  ( 553 )
32 Experimental study on wave attenuation characteristics of rigid-flexible combined wavebreak forests
ZHOU Yue, DONG Zengchuan, CAO Haijin, XU Wei, SUN Biao, REN Jie, WEI Yiming
DOI: 10.11660/slfdxb.20190304
A wavebreak forest combing rigid and flexible vegetation is founded out through experimental tests on the water attenuation property of different wavebreak forests in this study. This combination is specific to rivers with significant seasonal variation in water level, and it seems to ensure a better wave breaking performance of ecological revetment projects. We conduct wave breaking tests on four combined types of rigid and flexible vegetation under eight different water levels, considering the height of existing wavebreak forests and the measured water levels in the Laolongkou reach. Results show that in different inflow conditions, a large disparity in the wave-breaking effect of a wavebreak forest of the single vegetation type is observed, while the combined vegetation types produce an improved, stable effect. The transmission coefficients of rigid-flexible combined wavebreak forests are smaller than 58%. Different type of vegetation has its own superiority in water attenuation under different water levels, and such an advantage can be utilized and integrated by a combined type adequately. Therefore, a combined type can achieve better, stable effect in water attenuation, making it more cost-efficient and reasonable to construct rigid-flexible wavebreak forests within rivers featured with a wide range of fluctuations in water level. The results would help the design of ecological revetment projects on rivers similar to the Laolongkou reach.
2019 Vol. 38 (3): 32-39 [Abstract] ( 225 ) PDF (1047 KB)  ( 564 )
40 Evolution of oases under human interference in arid Northwest China
WANG Yuding, ZHENG Hang, ZHAO Jianshi
DOI: 10.11660/slfdxb.20190305
Owing to intensified human activities in recent years, oases change rapidly in the major inland river basins in arid Northwest China: the four river basins of Heihe, Shule, Shiyang, and Tarim. Using the 2002-2012 land use data of this region, this paper explores the evolution of the oases in each basin. Results show that in this period, all the oases in the four basins were expanding. The woodland, grassland and waters (WGW) were relatively stable, while the socio-economic land was changing dynamically and significantly. The gravity center of oases was moving downstream in the Heihe River basin while upstream in the Shule River basin. In the transformation between oasis and desert, grassland and woodland contributed more than the other land use types. WGW turning into socio-economic land dominated the transformation between them.
2019 Vol. 38 (3): 40-52 [Abstract] ( 216 ) PDF (1481 KB)  ( 558 )
53 Quantitative assessment on influence of parameter uncertainties on runoff simulations
LI Ziyan, LIU Dengfeng, HUANG Qiang, BAI Tao, ZHOU Shuai
DOI: 10.11660/slfdxb.20190306
Hydrological modeling is a key tool for analyzing the hydrological process of a river basin, but uncertainties in its parameters reduce the accuracy and applicability. This paper examines the influence of parameter uncertainties on runoff simulations, using a variance decomposition method of factor analysis along with a case study of the runoff calculated with the Soil and Water Assessment Tool (SWAT) model. The results show that under different floods, the influence of parameter uncertainties on the simulations is obviously different and it is larger in the case of lower flows than higher flows. From more to less sensitive to hydrological responses, the parameters can be listed as: fraction of main channel transmission losses partitioned to the deep aquifer, effective hydraulic conductivity of the channel bed, and saturated hydraulic conductivity of soil. Interaction of the first or second parameters with the third also produces a significant influence on the simulations. This study would help reduce the impact of the parameter uncertainties in hydrological modeling.
2019 Vol. 38 (3): 53-64 [Abstract] ( 192 ) PDF (4039 KB)  ( 556 )
65 Multi-objective optimization of hydrological model based on runoff and snow data
HE Keqi, GAO Chao, XIE Jingkai, XU Yueping
DOI: 10.11660/slfdxb.20190307
This study applies the Hydrologiska Byr?ns Vattenbalansavdelning (HBV) model to simulations of snow and runoff processes in the upper Yalung Zangbu River over its basin above the Nuxia gauging station. We develop a multi-objective optimization method considering river runoff, snow depth, and snow coverage to calibrate the model’s parameters; and compare the simulation results with those considering only river runoff and snow depth. The results show that the HBV model based on measurements of runoff and snow depth simulates the runoff quite well, but its simulations of snow depth are poor. Adding snow coverage to the model calibration can improve the simulation accuracy of snow coverage significantly, and also improves efficiency coefficient of river runoff. Thus, changes in snow and runoff in the study area can be better predicted by this HBV model that is calibrated against the measurements of river runoff, snow coverage, and snow depth.
2019 Vol. 38 (3): 65-74 [Abstract] ( 339 ) PDF (1803 KB)  ( 782 )
75 Estimation of dam overtopping risk rate based on Copula functions
LIU Zhangjun, XU Xinfa, CHENG Jingqing, WEN Tianfu, ZHANG Fanping, XU Junkai
DOI: 10.11660/slfdxb.20190308
Flood overtopping risk rate is a key factor in reservoir operation and dam safety management. This paper estimates this factor based on Copula functions and analyzes its dependency on the selection of these functions and the correlation between flood peak and volume. We apply the Gumbel-Hougaard Copula function to an analysis of the Geheyan reservoir in the Qing River basin, and demonstrate that its optimal form can better describe the upper tail dependence between flood peak and flood volume, while the Frank and Clayton Copula functions underestimate the risk rate significantly. For this reservoir, the estimated flood overtopping risk rate is 3.79×10-5, but it increases as the correlation between flood peak and volume increases. In the cases of full correlation it is overestimated while underestimated in the independence cases. Our bivariate statistical approach based on Copula functions, through effectively capturing the dependence between flood peak and volume, improves the estimation of overtopping risk rate and would be useful for overtopping risk analysis.
2019 Vol. 38 (3): 75-82 [Abstract] ( 224 ) PDF (2973 KB)  ( 619 )
83 Allocation of sector reservoir water rights based on reservoir assets allocation
WANG Helong, LI Qifeng, WEN Jinhua, WANG Shiwu
DOI: 10.11660/slfdxb.20190309
Allocation of water rights is key to the registration of water resources and the foundation for implementing market allocation of water resources. Based on the theory of property rights economics, this study examines the property rights subjects and the allocation of reservoir’s water resources assets, reservoir project assets, and aquatic ecologic space assets. We construct a sector water rights allocation system that can describe the allocations results of the subjects and reservoir assets, and develop a method for determining the water resource use right quantity of the reservoir’s jus in re propria and jus in re aliena and a method of sector water right allocations. Results show that the incorporation of reservoir property rights and the asset allocation theory into this allocation system conforms to the basic principles of property rights economics, helping protect the legitimate rights and interests of all the investors in reservoir construction as a useful exploration to guide the registration of natural resources in China. The allocation of reservoir’s sector water right quantity is beneficial to promote the construction of a water resources property right system with well-defined power and responsibility, and it would also lay a basis for water administration departments to carry out the approval work of water intake permits for different sector users.
2019 Vol. 38 (3): 83-91 [Abstract] ( 180 ) PDF (500 KB)  ( 474 )
92 Fault diagnosis for hydropower units based on fractal and probabilistic neural network
LI Hui, LI Xintong, JIA Rong, LUO Xingqi, ZHAO Jixing
DOI: 10.11660/slfdxb.20190310
Vibration signals from a hydropower unit are non-linear and non-stationary, but they are similar in different scales and typical of fractal features. This paper reports a multi-fractal method of fault diagnosis for hydropower units, analyzing the vibration signals, extracting their generalized dimensional spectral features, and diagnosing the fault with a probabilistic neural network optimized by the artificial fish swarm algorithm. A case study shows that this method, through combination of multi-fractal and probabilistic neural network, can accurately distinguish fault types. Compared with a BP or RBF network, it achieves a higher diagnostic recognition rate and faster speed, thus providing a more reliable tool for unit operation and maintenance personnel.
2019 Vol. 38 (3): 92-100 [Abstract] ( 223 ) PDF (520 KB)  ( 403 )
101 Application of quick-then-slow closing rule for turbine wicket gates
LI Min, ZHANG Jian, YU Xiaodong
DOI: 10.11660/slfdxb.20190311
Optimizing the closing rule of turbine wicket gates is crucial to the calculations of guaranteed regulation for hydropower stations. A reasonable closing rule can reduce water hammer pressure and limit hydro turbine unit speeds, providing an effective, economical measure. In this work, we develop a mathematical model for the transient process in a water diversion system of a hydropower station, conduct simulations of the process under the control conditions of the station, and examine the influence of closing rules of turbine wicket gates on the diversion system. Results show that quick-then-slow closure is an effective rule applicable to the hydropower stations where extreme water hammer pressure and extreme rotational speed occur in different working conditions. And for this type of hydropower stations, this rule can overcome the problem with the direct closing rule that cannot meet the requirement by guaranteed regulation.
2019 Vol. 38 (3): 101-107 [Abstract] ( 274 ) PDF (366 KB)  ( 600 )
108 Surge characteristics of gas-liquid two-phase centrifugal pumps under part-load conditions
LUO Xingqi, YAN Sina, FENG Jianjun, ZHU Guojun, ZHANG Lefu, CHEN Senlin
DOI: 10.11660/slfdxb.20190312
Gas-liquid two-phase centrifugal pumps are widely used in agriculture, water environment, nuclear industry, and petroleum industry. Centrifugal pumps perform most efficiently when operating under single-phase flow conditions. However, the presence of gas causes head degradation, low efficiency, and low hydraulic performance; and surge is one of the most serious problems faced by gas-liquid two-phase centrifugal pumps. In this work, the commercial software ANSYS CFX 16.0 is adopted to calculate the three-dimensional turbulent flows in a centrifugal pump with a mid-low specific speed impeller. From the results, we can find out that at the pump inlet, gas gathering becomes increasingly obvious and the gathering area is growing larger with the increasing gas volume fraction at the inlet until a surge occurs. Subsequently, a large amount of gas gathers in the impeller channel and even blocks its passages completely, which is known as surge. To improve the hydraulic performance of the pump under surging conditions, we apply a cavity structure to the pump, and examine in detail its effects on the external characteristics and internal flow field. The results show that under low flow rates, the cavity structure can improve blade pressure distribution and uniform gas phase distribution in the impeller channel, effectively reducing the gas blockage of the pump. This study shows that the cavity structure cannot only balance the pump impeller and reduce the pump weight, but reduce the phenomenon of gas-liquid separation in the flow field.
2019 Vol. 38 (3): 108-115 [Abstract] ( 262 ) PDF (758 KB)  ( 472 )
116 Experimental study on seepage deformation of unsaturated gravel clayey soils
TIE Mengya, ZHANG Yinqi, DENG Gang, WEN Yanfeng, ZHANG Yanyi
DOI: 10.11660/slfdxb.20190313
In this study, experimental tests on seepage deformation of unsaturated gravel clayey soils are carried out, and the influence of soil saturation conditions and hydraulic gradient loading on the capability of wide-graded gravel clayey soil against seepage failure is studied. Results show that the saturation condition has a great influence on the capability against seepage failure. A pre-saturated soil sample can bear a larger hydraulic gradient before piping failure, while the failure occurs at a certain hydraulic gradient when the sample is not pre-saturated. All the unsaturated gravel soil samples fail when a relatively large hydraulic gradient is applied in a single stage. An increase in hydraulic gradient decreases the elapsed time at which fine particles begin to be brought out and the elapsed time at piping failure. Decreasing fines content also leads to a decline in the sample’s resistance to piping failure. For gravel soils with the same dry density and water content, the failure hydraulic gradient decreases with the decreasing fines content. The anti-piping capability of gravel soil is obviously improved by adding a filter protection, but the soil, even so protected, may still fail due to piping if its fines content is low.
2019 Vol. 38 (3): 116-124 [Abstract] ( 203 ) PDF (575 KB)  ( 464 )
125 Foundation treatment for spillway control section of Qianping reservoir
LI Congshi, HUANGFU Zehua, PENG Guanghua, TANG Jianli
DOI: 10.11660/slfdxb.20190314
In the spillway control section of the Qianping reservoir, excavation to the foundation surface reveals its geological conditions greatly different from the survey data obtained previously. A supplementary geological survey verified that this section is actually located in a contact zone between andesitic porphyrite and diabase with its base plane mostly on a strongly weathered deep bedrock. The weathering degree of diabase rock is non-uniform with the maximum exposure depth of 10.2 m at the exploration hole; the nature of rock mass is heterogeneous, featured with a soft-hard interphase layer and a potential risk of local stress concentration and uneven settlement. To solve these problems, we optimize the foundation treatment of the spillway control section and achieve the treatment goals through several measures such as excavation and replacement of concrete, anti-slide piles, and reinforced concrete anti-slide slots.
2019 Vol. 38 (3): 125-134 [Abstract] ( 168 ) PDF (1519 KB)  ( 565 )
135 Experimental study on deformation characteristics and shear strength of rockfill under freeze-thaw cycles
CHEN Tao, BAO Qichang, WANG Wei, YIN Yin, ZHANG Bingyin, SUN Xun
DOI: 10.11660/slfdxb.20190315
Freeze-thaw cycling is an important factor affecting the safety of high earth-rock dams in severe cold regions. This paper presents the results of freeze-thaw cycling tests on the rockfill materials of the Rumei project, a high core wall rockfill dam on the Lancang River, Tibet. We conducted the tests using rockfill weathering test apparatus developed by Tsinghua University, together with direct shear tests under the conditions of different normal stress. Deformation and strength characteristics of the rockfill materials under freeze-thaw cycling were then examined. Test results show that during a given freeze-thaw cycle, a rockfill sample undergoes three typical stages: thaw shrinking, frost shrinking, and frost heaving. On completion of the freeze-thaw cycles, the sample starts a large back expansion deformation, reducing its compactness and shear strength. The reduction in shear strength is about 11.5% to 15.4% in the case of 20 freeze-thaw cycles.
2019 Vol. 38 (3): 135-141 [Abstract] ( 171 ) PDF (418 KB)  ( 587 )
142 Fuzzy comprehensive evaluation of earth-rock dam compaction quality based on real-time monitoring
LIU Donghai, WU You
DOI: 10.11660/slfdxb.20190316
The traditional quality assessment method of earth-rock dam compaction is primarily based on control parameters collected from the job site of compaction and by sampled spots testing. Compaction parameters cannot satisfy the requirement by every location of the entire working surface, and using the same parameter may lead to different compaction quality due to the influence of inhomogeneity in material property. A limited number of test samples are usually an unreliable representation of compaction quality over the entire surface layer, and a certain error occurs when compaction value (CV) alone is used in the evaluation. This paper describes a fuzzy comprehensive compaction quality evaluation method based on the Dempster-Shafer evidence theory and dynamical monitoring of compaction parameters and CV. We also develop a concept of equivalent continuous weak area using the density-based spatial clustering of applications with noise (DBSCAN) to ensure that no obvious continuous weak area occurs in the compacted layer, and apply it to quantitative evaluation of the spatial distribution of weak areas. Case analysis shows that our evaluation method can effectively avoid one-sidedness in evaluating compaction parameters and enhance the comprehensiveness of compaction quality assessment, thereby providing a new way for quality control in earth-rock dam construction.
2019 Vol. 38 (3): 142-153 [Abstract] ( 178 ) PDF (2336 KB)  ( 493 )
154 Measures to reduce tensile stress in high asphalt concrete core walls
DANG Faning, GAO Jun, YANG Chao, MA Zongyuan
DOI: 10.11660/slfdxb.20190317
Traditional rockfill dams with an asphalt concrete core wall is featured with a linear shape of both the core wall and dam shell. The core wall is deflected by the horizontal pushing of water pressure, and its deflection deformation and the elongation of its axis may induce tensile stress. Generally, a higher dam may have a higher risk of tensile cracks developed in its core wall. In this study, we analyze the generation mechanism of tensile stress in a core wall, and develop two new dam types as improving measures ? a straight dam with a curved core (SDCC) and a curved dam with a curved core (CDCC). Finite element analysis is used to examine the influences of dam height and dam axis length on the deflection deformation and tensile stress in the core wall and to investigate the improving effect of these two types. Results show that a greater dam height, longer dam axis, and larger bank slope ratio of a traditional dam lead to greater tensile stress in its core wall, and consequently a greater reduction in tensile stress if it is modified into either of the two suggested dam types. Analyses on construction technique, construction period, and economic cost show that the new types of rockfill dams are feasible and may have a good application prospect.
2019 Vol. 38 (3): 154-164 [Abstract] ( 228 ) PDF (683 KB)  ( 585 )
165 Real-time evaluation of compaction quality of earth-rock dams using fuzzy logic based on KM and AC-BFA
WANG Jiajun, ZHONG Denghua, GUAN Tao, TONG Dawei, DENG Shaohui
DOI: 10.11660/slfdxb.20190318
This study develops a real-time compaction quality evaluation model to improve the low accuracy and robustness of the existing compaction quality evaluation models. This real-time model adopts a newly fuzzy logic based on the kernel method (KM) and adaptive chaotic bacteria foraging algorithm (AC-BFA). Its input parameters consist of the physical parameters of compacted material, such as the amplitudes of the first harmonic and fundamental wave decomposed from the vibration signal, the characteristic parameters of material source, and the rolling parameters of construction process. Engineering application shows that compared with the commonly used compaction quality evaluation models, the real-time model is more accurate and superior showing stronger robustness in noise data tests and abnormal data tests, and it can achieve real-time evaluation of compaction quality when embedded into a compaction quality real-time monitoring system.
2019 Vol. 38 (3): 165-178 [Abstract] ( 178 ) PDF (2332 KB)  ( 392 )
179 Wireless video reservoir monitoring system based on 3D real scene modeling
ZHANG Zhaosheng, MA Shanyu, HUANGFU Yingjie, LI Congshi, HUANGFU Zehua, ZHANG Yuming
DOI: 10.11660/slfdxb.20190319
During the construction of the Qianping reservoir, a wireless signal bridge was designed and applied to signal transmission, and a video surveillance system, based on the unmanned aerial vehicle (UAV) photography, was developed to generate three-dimensional real-time models for the monitoring points. This paper presents a method of the aerial photographer's oblique photography using the Dajiang unmanned aerial vehicle DJ1 PHANTOM4 PRO and a procedure for generating 3D real scene models using Context Capture 3D. We describe a method for optimizing the layout of monitoring points, visual field, and channel rechecking based on the 3D real scene model. Application shows that the wireless video surveillance system is reliable and useful for monitoring reservoirs and other similar projects.
2019 Vol. 38 (3): 179-185 [Abstract] ( 220 ) PDF (5521 KB)  ( 580 )
186 Explicit solution analysis of underground pipeline mechanical responses under tunnel construction conditions
ZHANG Wenjun, ZHU Zhankui, LI Yao
DOI: 10.11660/slfdxb.20190320
To study the influence of tunnel construction on the behavior of underground pipelines, this paper presents a modification to the formula for calculating the pipeline deformation based on the Winkler elastic foundation beam theory and previous related results. We also give an explicit solution in single line tunnel case and a new method of solving for the mechanical responses such as the bending angle, bending moment and shear force of an underground pipeline. The method is verified through calculations using MATLAB. By the superposition principle, we derive a method for direct calculation of the mechanical responses of a pipeline subjected to the construction of twin tunnels in parallel. Results show that the responses of such a twin tunnel case are significantly different from those of the single line tunnel case, and that the spacing of twin tunnels is a major factor influencing the responses. When the spacing is varied, the distributions of deformation and bending angle of the pipeline are nearly the same, but the peak magnitudes are always larger than those of single line tunnel case. And there exists a certain range of the spacing, beyond which the peak bending moment and peak shear force are larger than those of single line case. Within this range, both appear smaller. This study provides an effective method for calculating the mechanical responses of underground pipelines to ground movement under construction of single and twin tunnels, thereby helping safety evaluation of urban underground pipeline operation.
2019 Vol. 38 (3): 186-194 [Abstract] ( 186 ) PDF (568 KB)  ( 500 )
195 Numerical simulations of whole fracturing process of concrete under hydrostatic pressure
QING Longbang, SU Yimeng
DOI: 10.11660/slfdxb.20190321
This paper derives theoretical expressions of the external loads and crack opening displacements of concrete wedge-splitting specimens under hydrostatic pressure, based on the initial fracture toughness criterion and the Paris displacement formula. And a numerical iterative method is used to simulate the specimens’ full fracturing process, focusing on analyzing the effect of water pressure, particularly the sensitivity of the peak load parameters and the opening displacement parameters of critical cracks under different water pressures. The results show that the full crack propagation curves calculated using this method agree well with the experimental measurements. Water pressure and initial crack length affect load-displacement curves. With an increasing water pressure, both peak load and critical cracks’ opening displacement are reduced; with an increasing initial crack length, more obvious is the influence of water pressure on the full process curve of crack propagation.
2019 Vol. 38 (3): 195-202 [Abstract] ( 188 ) PDF (441 KB)  ( 464 )
203 Structural model tests of high-pressure hydraulic tunnels under high geotemperature conditions
PENG Lifeng, SU Guoshao, HU Xiaochan, QIN Zihua, HE Baoyu
DOI: 10.11660/slfdxb.20190322
To reveal the bearing characteristics of surrounding rock mass of hydraulic tunnels under the combined effects of high geotemperature and high internal water pressure, this study conducts experimental tests on a large-scale structural model of a hydraulic pressure tunnel with large geotemperature gradients in multi-physical fields through developing a similar material of complete hard rock mass. For the tests, we adopt acoustic emission techniques for signal monitoring and locating, develop a new loading technique of combined temperature loads and internal water pressure, and analyze the dynamic evolution processes of temperature field, pore pressure field, acoustic emission, and fracture propagation. Results show that compared to the condition without high geotemperature, the critical internal water pressure of the surrounding rock mass of the tunnel at the start of hydraulic fracturing is lowered obviously. In a high geotemperature environment, the induced cracks between the main fractures in the rock mass have evolved quite completely, manifesting the difference from the normal geotemperature cases where only a few main fractures are mobilized. And the rock mass has undergone an obvious coupling effect of thermo-hydro-mechanical fields, and the fracture propagation and increasing damage of the rock mass are featured with discontinued step evolution under constant water pressure. Under high in-situ stress conditions, the locations of hydraulic fractures and fracture propagation are influenced significantly by the lateral confining coefficient of in-situ stress.
2019 Vol. 38 (3): 203-217 [Abstract] ( 216 ) PDF (5652 KB)  ( 555 )
218 Influence of humidity on stress and deformation of simply supported concrete beams
YANG Le, LI Zongli, YAO Xiwang, DU Xiangqin
DOI: 10.11660/slfdxb.20190323
Swelling deformation in a concrete structure in direct contact with water inevitably causes changes in its performance. In this study, we develop a humidity diffusion model based on Fick's second law, conduct physical tests to determine saturated humidity diffusion coefficient, and verify the model against the test data of one-dimensional water absorption in concrete. The mechanism of humidity influencing the deformation of a simply supported concrete beam is studied through experimental tests and numerical simulations. And we analyze the simulations to examine humidity effect on elastic modulus, swelling effect on the deflection and strain distribution of the beam, and the combined effects of humidity and swelling on beam stress response. Results show that the model and its parameters adopted in this study are applicable to simulating nonlinear humidity distribution in a beam. The deflection and strain distribution are less affected by humidity change and its effect on elastic modulus, but they are greatly changed by the swelling caused by water absorption. The combined effect of their changes has a greater influence on beam stress response. Thus, we suggest that in designing concrete structures in direct contact with water, the effects of humidity should be considered.
2019 Vol. 38 (3): 218-226 [Abstract] ( 162 ) PDF (507 KB)  ( 480 )
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