Two reef-blasting schemes are proposed according to Wangjiatan river regime and beach conditions. By using a two-dimensional mathematical model, the two schemes are compared and analyzed.Two-step platform should be adopted in the reef-blasting project. The reef part within 30m of the channel boundary should be blasted until the water depth reaches 4.2m, and the rest blasted to 3.7m so that the undesirable flow patterns affected by shallow water platform could be eliminated. After the implementation of the project, the water depth of the second flat increased by 0.5m, the platform for navigation is widened, and the second platform is accessible for 3 000-ton ship. The ship sailing route moves towards the right and straightens, and the navigation channel is widened, which greatly improves the navigation condition.
Yingtiantan is located at the segment between Haohekou and Chenglingji. It is a flood channel of Dongting Lake and has typical characteristics of rivers and lakes with complex shoal evolution. In recent years, riverbed has been damaged seriously by activities of sand excavation. Regulation actions are proposed in order to improve the channel level in the first-stage of Xiangjiang 2000t channel construction project. The effect of the proposed regulation actions are analysed by using 2-D mathematical flow model and the results indicated that the proposed two design schemes could both meet the design requirements. The right branch scheme is recommended because the flow condition in the channel is not affected by the confluence of the upper and lower stream opening. It could also contribute to local economic development.
The water flow and sediment in Yangtze River have changed remarkably since the operation of Three Gorges Reservoir. To provide guarantee and basis for the simulation of hydrological conditions in sediment model calculation, we statistically analysed the variation of sediment in the middle-lower Yangtze River since the Three Gorges Reservoir impoundment. On this basis, we carried out detailed research on the sediment problem of hydrological year of designed frequency which is often selected in sediment model calculations and tests. We proposed the method and approach of dealing with sandy sediment in sediment model which is to deduce the sediment process of designed flood according to the relationship between flow rate and sediment transport rate. Moreover, in consideration of project safety, we proposed to take the lower enveloping curve of flow rate versus sediment transport rate as the basis of determining sediment process. Through this method, the sediment condition in hydrological year of designed frequency when sediment load decreases could be well reflected.
Acid mine drainage (AMD) is of great harm to the environment as it contains rich heavy metal ions such as Copper, Lead, Zinc, and Cadmium. The main causes and harms of AMD is analyzed, and the techniques currently used to treat AMD is summarized and their advantages and shortcomings are analyzed. Moreover, the research progress and development trend of treatment technology for AMD in China and abroad are presented through a brief introduction of new treatment technologies. The necessity and inevitability of developing efficient, low-cost, safe and convenient treatment technology are expounded.
By analysing main factors affecting the migration and conversion of ammonia-nitrite-nitrates in groundwater, we aim to provide theoretical basis for the prevention and control of agricultural non-point source nitrogenous pollution. Qianyanzhou test station in Jiangxi Province was selected as research object and experiment plots were divided. The groundwater table, ammonia-nitrite-nitrates, ferrum-manganese and pH value of groundwater in the research area were monitored in long term. Through data sorting, diagram analysis and SPSS software, we analysed the correlation among ammonia-nitrite-nitrates, total iron, manganese in filtering state and pH value. Results suggest that the groundwater in the study area has been affected by agricultural non-point nitrogenous pollution. Ferro-manganese in groundwater are apparently associated. Ammonium nitrogen and nitrite nitrogen are positively related with ferro-manganese. Total iron, manganese in filtering state, pH value, temperature and rainfall are the main impact factors of the transport and transformation of ammonia-nitrite-nitrates in the groundwater.
Saltwater intrusion in Qiantang River has threatened the drinking water safety of Hangzhou city especially when upstream runoff descends. The topography varies fiercely as upstream runoff changes with different seasons and years. To reveal the influence of topographical descending on saltwater intrusion in Qiantang River we built a model to simulate the variation of hydrodynamics and salinity in the reach from Wenjiayan to Cangqian in the presence of spring tide, moderate tide and neap tide, and employed finite volume method to discrete the space. The result shows that the computation values of tidal level and salinity are consistent with the measured data. When the section of Zhakou station descends 1.6m and Qibao station 1.1m in average, the tidal range increases 22cm at Zhakou and 9cm at Qibao. The salinity line (0.5) moves 3.7km upwards and the maximum salinity at Qibao increases 17%. The salinity at the convex bank of Qibao section changes more strongly than that in the adjacent of thalweg, therefore the increment of salinity caused by topographical descending exerts more influence on water intakes at convex bank than those at concave bank.
It is important to have a universal standard when assessing the scale of a flood disaster, despite such a widely accepted standard does not currently exist. On the basis of fuzzy clustering iterative model, we proposed a calculation method for disaster standard independent of the time and location of the disaster. A piecewise linear chaotic map based culture differential evolution algorithm was used to optimize the objective function. We verified the efficiency and accuracy of this method by applying it to the data of flood happened in Sichuan province during 1976-2006. The results are reasonable and consistent with the distribution of the flood disaster according to the assessing standard currently used by the Sichuan province. This method can also be applied to the flood disaster assessment in most cases which have complete data.
In recent years, earthquakes occurred frequently in the Southwest of China, damaging dams in the region to different extents. Assessment on the seismic damage is necessary to exploring the risk and damage regularity for reservoirs and dams. Fourteen dams in the upstream of Minjiang River after “5·12 Wenchuan earthquake” are selected as evaluation objects. Moreover, impact factors inclusive of project design, operation and management, seismic properties and earthquake damage characteristics are considered, and 11 indexes are selected to form an index system and their weights are determined as well based on the criterion layer. Furthermore, synthetic index method of analytic hierarchy process is used to establish a model of comprehensive assessment. The model is applied to calculate the seismic damage status of 14 dams and discriminate the importance degree of each impact factor. The assessment result is almost consistent with the site investigation, which confirms that the evaluation indexes and their weights are reasonably determined. The result is an important basis for relieving earthquake damage scientifically for large or medium-sized hydropower projects.
Unlike ordinary slope, dump slope is made of loose media and its stability is greatly affected by rainfall infiltration. In order to quantitatively study the impact of rainfall as well as waterproofing and drainage measures on the stability of dump slope, firstly, we built a numerical model of dump slope seepage under rainfall infiltration to analyze the internal seepage field; and then through soil and water coupling analysis we found that the safety factor of dump slope decreased remarkably in rainfall condition. In order to serve the engineering and scientific research, we further studied the stability of dump slope under seepage-proofing or drainage conditions. Results suggest that drainage pipes in the bottom of the slope terrace or seepage-proofing layer on top of the slope could greatly improve the slope stability under rainfall infiltration. The research result provides basis for the design and regulation of dump slope.
The flow structure in ipsilateral vertical slot fishway is researched by changing the relative width of vertical slot (0.05, 0.10, 0.15, 0.30) and bottom slope 10% in a fishway model. Visual display and data analysis are adopted in the research. Through the simulation, the flow velocity distribution along water depth, the frictional distribution and attenuation of maximum flow velocity in mainstream area, as well as the turbulence kinetic energy distribution in the presence of different relative slot width and different flow velocity are obtained. Results reveal that when vertical slot width b0/B=0.15 and bottom slope is 10%, flow pattern favorable for fish migration could be formed in the pool: the range of transverse diffusion of flow in mainstream area is moderate, the maximum flow velocity in the mainstream area attenuates uniformly along the way, and the backflow area is symmetrical with small flow velocity.
The type and layout of crucial parts of high-head shiplock’s water conveyance system is introduced in this paper. The paper is based on research achievements in China and abroad as well as in the Yangtze River Scientific Research Institute since its founding half a century ago. The basic pattern of dynamically balanced conveyance system which fits different chamber sizes and water heads is introduced. A new idea of solving the lip cavitation of reversed tainter valve is presented, and a new type of dispersed conveyance system with double energy-dissipation systems (internal stilling pool and external dissipation plate) of higher dissipation efficiency is proposed. This paper could offer a reference for researchers and designers in this regard.
Prediction of the aging deformation of pile-soft rock composite foundation depends on the understanding of rheological mechanism and the description of the rheological model. The rheological mechanism of pile-soft rock composite foundation was researched by analyzing the aging characteristics of pile stress, tip resistance of piles, pressure in rock surface under pile cap, and deformation in the deep of soft rock through scale model loading creep test. Results indicated that the tip resistance of piles and the deformation of soft rock between piles are both with obvious aging characteristics. The decay creep of the composite foundation under engineering loads can be accurately described by generalized Kelvin model with five parameters. The values of the five model parameters are as follows: EH=1.1 GPa, E1=7.05GPa, η1=929 GPa·h, E2=9.03 GPa, η2=28 GPa·h. The rheological parameters of the composite foundation are significantly higher than those of soft rock foundation.
Ordinary electrical method is inefficient in the measurement of retaining wall, while high-density electrical method has better efficiency as it is based on the electrical prop of different underground geological bodies according to the distribution regularity of conduction current of strata. Therefore it was used in the measurement of retaining wall at the left bank of mainstream Nanshilichanggou River, and the result showed that, the height of the wall is about 2.3m, the depth of potential water level in the earth behind the wall is about 3.1-3.8m, cavities in the retaining wall and the earth are found in partial positions but are not developed in general, the thickness of the wall does not change a lot. The result is consistent with those from geological radar and practical excavation, indicating that high-density electrical method is feasible to measure retaining wall.
The soil-water characteristic curve is divided into four segments based on the main factors affecting the hydraulic conductivity coefficient of unsaturated soil. On this basis, a segmentation simplified model for hydraulic conductivity of unsaturated cohesionless soil with bad gradation was created. A complete predictive curve can be obtained just with a small amount of measured or calculated hydraulic conductivities of different moisture conditions. Curve of lnK-lnΨ at low matric suction(0<ψ<ψa)and curve of lnK-lnθ when θb<θ<θa are verified to be linear.
Goodman-Bray Method is commonly used in the stability analysis for toppling rock slope, but the effect of groundwater is not considered. In view of this, we made an improvement to the Goodman-Bray method by deducing the stability calculation of toppling rock slope in consideration of groundwater effect, and wrote calculation program by using MATLAB. With a toppling rock slope in Wuxi, Chongqing City as a case study, we verified this improved Goodman-Bray method using Sarma Method and Transferring Coefficient Method (TCM) for comparison. Results suggest that the improved Goodman-Bray method and Sarma Method which combines rock block and structural planes could better reflect the practical situation than TCM because of the limits of toppling rock mass. But the connectivity of block bottom is neglected by using Sarma Method so that the calculation result is smaller than practice. So this improved Goodman-Bray method is more suitable to be used for stability analysis of toppling rock slope in consideration of groundwater effect.
Three-dimensional finite element method is used to analyze the stress and deformation behavior of cut-off wall of concrete faced rockfill dam on deep overburden foundation. The Duncan-Chang E-B model is used to simulate the constitutive relationship between rockfill and overburden material. The contact friction elements are set to simulate the interaction between the concrete structures and the overburden and cushion materials. The influences of staged-filling scheme, construction rate of dam body and construction sequence on stress-deformation behavior of the cut-off wall are discussed. In addition, the stress-deformation behavior of the suspended cut-off wall is also analyzed. Based on the numerical analysis, it is concluded that the staged-filling of dam body has small impact on the stress and deformation of the cut-off wall, whereas high construction rate may cause large stresses and displacements of the wall during completion period (tensile stress reaches 3MPa, deformation along the river direction amounts to 15cm), and the sequence of constructing cut-off wall in later stage could reduce the tensile stress by 2.42MPa and the deformation along river direction by 85%. A small depth of suspended cut-off wall could also improve its stress and deformation behavior.
Geological disasters occurred frequently since the impoundment level of Three Gorges reservoir area reached 175mm. Especially in Wu Gorge where the geological environment is vulnerable, an amount of 380 000m3 collapsed at Gongjiafang slope in 2008, causing surge waves of 13m high, severely affecting the safety of waterway transportation. Through data gathering, ground investigation, engineering geology surveying and mapping, we researched the engineering geology and bank slope structure, and identified 18 potentially unstable slopes according to the bank slope’s deformation and failure features. Analysis shows that the deformation failure mode are composite bending-toppling, V-shape toppling and interlayer shear failure, which would give rise to toppling and sliding instability. There are three failure mechanisms: progressive failure, brittle failure in “locked area” and integral failure. The research achievements provide reference for similar high steep bank slope research in the future and for disaster prevention and mitigation in Three Gorges area.
The intake slope of the spillway tunnel of a hydropower station is a typical high steep rock excavation slope. Its stability has a significant impact on the safe construction and operation of the station. In this research, 3-D finite element model is established for the slope and stability analysis is conducted by using finite difference software. The stress, strain, and the size and distribution of plastic zone in natural condition, excavation and deloading condition, rainstorm and seismic conditions are comprehensively considered in the model. Furthermore, according to the safety factor from two-dimensional limit equilibrium calculation for typical profile, the slope stability is determined. Moreover, the reinforcement measures are optimized based on the stability calculation results.
Due to the complexity of drainage consolidation of red clay foundation, we simulated and analyzed the consolidation settlement by using the consolidation calculation module Soils and modified Cambridge model of ABAQUS/Standard. The reconstruction project of an aluminum factory was taken as an example. The variation of red clay foundation’s settlement with time, the dissipation of pore water pressure, the non-linear distribution of void ratio with depth, and the effective stress growth of soil were researched. Results suggest that the calculated results are in good agreement with the law of soil mechanics, and the actual situation of the red clay foundation consolidation settlement could be reflected accurately. This research provides references for the foundation treatment and engineering design of buildings on red clay ground.
The influence of the dip and inclination of joint and the ratio of soil thickness to rock thickness on the stability of jointed rock slope with overlying soil is researched in the present paper. The Mohr-Coulomb and Ubiquitous-Joint constitutive models and strength reduction method are used. Results of numerical simulation reveal that: for consequent-joint slope, when the consequent angle of joint is approximately equal to the internal friction angle of the rock, the safety factor is small and the damage area is large; while for anti-dip rock slope, the safety factor is large when the joint intersects vertically with the potential damage fracture of the slope. The effect of the dip of joint on slope stability reduces with the slope angle increasing. When the dip of joint is larger than the slope angle, slope angle is the main factor affecting the slope stability. When the thickness of soil layer is less than 4 meters, the slope safety factor increases with the thickness of soil layer increasing, and vise versa. When the thickness of the overlying soil is small, the slope toe should be the focus of support work, while the air side of the overlying soil should be supported as the key position when the thickness of the overlying soil is close to or larger than half of the slope height.
The effect of initial seam-height ratio on concrete’s fracture performance was researched through wedge splitting test. Four groups including 32 specimens with different initial seam-height ratio were tested. The eigenvalues of parameters and the corresponding process curves of complete load, crack opening displacement and concrete surface strain were determined. Fracture parameters inclusive of effective crack length ac, initial fracture toughness KiniIC and unstable fracture toughness KunIC were calculated based on double-K fracture theory. Results indicate that along with the increase of seam-height ratio, the effective crack length ac increassd and the subcritical crack propagation length Δac reduces; KiniIC is not affected by the initial seam-height ratio, and KunIC increases with the reduction of seam-height ratio, but when a0/D≥0.5, it can be considered as a constant.
The concrete plugging of bottom diversion outlet has high proportion of cement, posing big challenge to the temperature control, therefore pipe cooling is needed. In this research, we recommend to combine the heat pipe cooling calculation formula with the measured temperature of concrete block, which means to dynamically update Ti in the heat pipe cooling calculation formula according to the measured temperature, and then predict the dynamic temperature of concrete block of n days in the future to guide and control the pipe cooling. The dynamic prediction for concrete temperature is proved to be feasible by the practical example of concrete temperature of plugging of bottom diversion outlet at Xiangjiaba Hydropower Project.
In order to study the dynamic damage features and damage evolution regularity of concrete, we carried out uniaxial compression test on concrete under different loading rates (10-5/s,10-4/s, 7.5×10-3/s) and collected the real-time acoustic emission signals. By analysing the relationship between acoustic emission parameters and stress-strain, we obtained the plastic deformation and damage features of concrete under cyclic loading and unloading. Results reveal that the damage concentrates in the early and middle stages of the cyclic loading and unloading process.The damage intensifies with the increase of loading time and cycle numbers. Damage variable also increases along with the increase of accumulated residual plastic strain. Moreover, when loading rate increases, the energy release before the peak gets larger and damage path becomes shorter. When the difference between loading rates gets larger, the damage path difference becomes larger, but the start point and end point of damage curves overlap.
Groundwater in seasonal frozen ground migrates towards the freezing front by capillary action when frozen. Several freeze-thaw cycles maybe experienced in a very short time during the frozen process in regions of high-altitude or large temperature difference between day and night. In view of this, a unilateral freezing triaxial apparatus for freeze-thaw cycle was developed. Unidirectional freezing test under the condition of filling water and triaxial shear strength test of freezing and thawing cycle can be conducted in the apparatus. Unidirectional freezing test on silty clay was conducted and the results show that CT numbers of the cross sections of samples decrease during the frozen process. The freezing front moves from the cross section of lower temperature to the cross section of higher temperature. The test result reflects the migration process of the freezing front during unilateral freezing.
