土层结构对管涌发展影响的试验研究

不同的土层结构对管涌的发生发展有着很大影响,对3种典型的土层结构进行了管涌发展的砂槽模型试验,观察并分析了管涌发生、发展的机理和过程。试验结果表明,双层堤基的砂砾石表面夹一层很薄的无黏性粉细砂时,管涌破坏前出水口的流量很小,临界水力梯度也较小,管涌破坏发生后通道发展速度很快,较短的时间内就会贯通,管涌破坏的机理与双层堤基不同;而在砂砾石层一定深度内夹有一层粉细砂将使堤基管涌破坏的临界水力梯度大大提高,然而一旦管涌破坏发生后涌砂量和侵蚀速率将很大,形成的通道深度较大,若不及时采取有效措施,当通道规模发展到一定程度后,通道上部会发生塌落而使堤坝产生溃口,进而使堤坝溃决。     

Application of modified complementary reservoir approach in analysis of water distribution networks under pressure-deficient conditions

Hydraulic simulation models which simulate water distribution systems in different operating conditions are essential tools to evaluate network reliability. Simulation models found in most commercial software are not effectively capable of analyzing demand nodes under critical conditions such as fire-fighting demand or network pipe breakage. In the current study, a combination of hydraulic model and complementary reservoir solution (CRS) method is used for solving network's problems in critical conditions for both series-looped networks and a part of water network in Ilam city (Iran). Obtained results show that CRS provide more than actual need on the demand node for some reservoir total pressure heads. Thus, two modified versions of CRS method are proposed to deal with failures of CRS in such cases. Obtained results demonstrate improved efficiency in the combined model for analyzing networks in abnormal conditions.     

Tenability conditions and filling times for fires in large spaces

Motivated by recent demands on regulatory reform, closed form solutions are developed for the filling times and upper layer temperatures for fires in large spaces including the volume expansion term that was neglected in previous similar efforts. The solutions evolve from (a) utilizing the air entrainment to a buoyant plume from a point source having the same convective heat release as the fire and (b) applying an energy balance for the hot layer. Heat losses to the surfaces of the enclosure and provisions for smoke control by natural ventilation are also considered in an approximate way. Although analytic solutions for the filling times exist in the literature if the volume expansion term is neglected, this work is the first to (a) present analytic solutions for the upper layer temperature including the volume expansion term and (b) incorporate heat losses and smoke control by natural ventilation. The present predictions agree with recent numerical results (Fire Sci. Technol. 19(1) (1999) 27), which agree with experimental data and consequently, the present results in turn agree well with experimental data (Fire Sci. Technol. 19(1) (1999) 27). They are also corroborated by asymptotic analysis worked out in Appendix A. For certain large spaces, the results show that critical times for evacuation or rescue operations from fire brigade depend on the upper layer temperature reaching high enough values to cause harm by radiation to occupants or fire fighting rescuers. Thus, critical times in large spaces do not result from the smoke layer descending below a critical height (e.g. 2.1 m from the floor), as they do for small spaces. The present results for large spaces having high ceiling clearance do not agree with CFAST calculations because the entrainment equation for the fire plume in CFAST is different from the one in this work.     

新型预应力钢筒混凝土顶管受力特征试验研究

城市供水能力不足与供水安全保障脆弱等问题一直制约着城市的发展,为实现特大山地城市供水组团与水库资源间互联互通需修建大量引水隧洞,而在岩质地层引水隧洞顶管法施工中预应力混凝土管节(JPCCP)抗裂问题一直是施工及运营管理极切关注的重点。本文采用现场顶进原型试验方法开展了预应力混凝土管节在轴向顶力作用下内外层混凝土应变、内外表面混凝土应变及混凝土管节裂缝开展研究。研究结果表明:(1)JPCCP管节在轴向加载过程中,内外层应力分布形式一致,但外层应力远大于内层,受偏心加载影响,管节应力在纵向传递中均出现偏心方向变化;(2)管节端口内侧混凝土是最薄弱区域,加载到顶力设计荷载的2/3左右时,在端口附近开始出现裂缝,且随着荷载增加沿环向发展,最终接近贯通;(3)推导了轴向荷载作用时JPCCP管承载特性计算公式,并与试验进行了对比验证,为类似结构的计算提供了理论基础。     

Design and validation of the THMC China-Mock-Up test on buffer material for HLW disposal

According to the preliminary concept of the high-level radioactive waste （HLW） repository in China, a large-scale mock-up facility, named China-Mock-Up was constructed in the laboratory of Beijing Research Institute of Uranium Geology （BRIUG）. A heater, which simulates a container of radioactive waste, is placed inside the compacted Gaomiaozi （GMZ）-Na-bentonite blocks and pellets. Water inflow through the barrier from its outer surface is used to simulate the intake of groundwater. The numbers of water injection pipes, injection pressure and the insulation layer were determined based on the nu- merical modeling simulations. The current experimental data of the facility are herein analyzed. The experiment is intended to evaluate the thermo-hydro-mechano-chemical （THMC） processes occurring in the compacted bentonite-buffer during the early stage of HLW disposal and to provide a reliable database for numerical modeling and further investigation of engineered barrier system （EBS）, and the design of HLW repository.     

A hybrid neural-genetic algorithm for reservoir water quality management

A combined neural network and genetic algorithm (GA) was developed for water quality management of Feitsui Reservoir in Taiwan. First, an artificial neural network (ANN) model was employed to simulate the behavior of nutrient loads into the reservoir. The data from watershed loads, precipitation in the watershed, and outflow were used in the ANN model to forecast the total phosphorus concentration in the reservoir. A 6-year (1992-97) record of water quality data was used for network training, and additional data collected in 1998-2000 were used for model verification. Further, a GA was used with this ANN model to optimize the control of nutrient loads from the watershed. The GA was used as a search strategy to determine the proper reduction rates of nutrient loads from the watershed so that the objective function could be as close to the optimal value as possible. The study results indicate that the ANN model can effectively simulate the dynamics of reservoir water quality. The GA is able to identify control schemes that reduce the in-reservoir total phosphorus concentration by as much as 60%, and water quality in the reservoir can be expected to achieve an oligotrophic (most of the time) or mesotrophic level if the watershed nutrient loads are reduced by 10-80%.     

Experimental strain analysis for polyethylene pipes installed by horizontal directional drilling

The results of five field tests on instrumented polyethylene (PE) pipes installed using horizontal directional drilling (HDD) are presented in the paper. The focus is on mechanical behavior of pipes, their stiffness, strength and deformations. The testing methodology is presented and correlation between different readings is discussed. The test results are presented in a form of pipe strains along the borepaths and vs. time of installation. The test program involved 200 mm (8 inch) diameter, standard dimension ratio (SDR) 17 and 150 mm (6 inch) diameter, SDR 11, high density and medium density polyethylene pipes pulled along 90 and 177 m borepaths. The parameters were the quality of the drilling fluids, the ratio of borehole to pipe diameters, pipe material, and construction sequence. The presented results show the variation of pipe strains with time and along the borepath. Strain gauge readings indicate both flexural and axial deformations. Included in the paper are also readings from a load cell indicating the value of the pulling force. The experimental results are analyzed in terms of different mechanisms that contribute to the increase of the pulling forces and straining of the pipe. Influence of the field test parameters is presented. Conclusions are drawn on the effects of the mechanisms and test parameters on the pipe mechanical behavior.     

Numerical simulation of the lateral pipe intake: flow and sediment field

Hydraulic characteristics of the flow and sediment transport conditions are among the most important issues in design of the lateral intakes in order to minimize the flow loss. In this study, a 3D numerical model has been employed in a parametric study to study the performance of a lateral pipe intake. Observations indicated that the flow was affected by the pipe intake so that the recirculation area was close to the wall of the main channel, the wall of the lateral pipe intake and back of the lateral pipe intake. The pipe intake in vertical direction to the main channel showed the highest performance, although sedimentation behind the pipe intake in this diversion angle was higher. In addition, pipe intake showed a quite acceptable performance for almost 40% intrusion to the main channel width. Relationships for the coefficient of discharge were also developed.     

The critical ventilation velocity in tunnel fires—a computer simulation

In ventilated tunnel fires, smoke and hot combustion products may form a layer near the ceiling and flow in the direction opposite to the ventilation stream. The existence of this reverse stratified flow has an important bearing on fire fighting and evacuation of underground mine roadways, tunnels and building corridors. In the present study, conducted by the National Institute for Occupational Safety and Health, a CFD program (fire dynamics simulator) based on large eddy simulations (LES) is used to model floor-level fires in a ventilated tunnel. Specifically, the critical ventilation velocity that is just sufficient to prevent the formation of a reverse stratified layer is simulated for two tunnels of different size. The computer code is verified by checking the computed velocity profile against experimental measurements. The CFD results show the leveling-off of the critical ventilation velocity as the heat release rate surpasses a certain value. At this critical ventilation, the ceiling temperature above the fire reaches a maximum for both tunnels. The velocity leveling-off can be explained from this observation. An extended correlation of Newman (Combust. Flame 57 (1984) 33) is applied to the temperature profiles obtained by CFD. At the critical ventilation, temperature stratification exists downstream from the fire. The computed critical ventilation velocity shows fair agreement with available experimental data taken from both horizontal and inclined fire tunnels. The CFD simulations indicate that the Froude modeling is an approximation for tunnel fires. The Froude-scaling law does not apply to two geometrically similar fire tunnels. The CFD results are compared with two simple theories of critical ventilation by Kennedy et al. (ASHRAE Trans. Res. 102(2) (1996) 40) and Kunsch (Fire safety J. 37 (2002) 67).     

超浅层顶管施工引起路基地层移动数值模拟

覆盖土层薄的超浅层顶管穿越路基施工引起管道周围土体移动会对路面结构造成破坏。结合实际工程,运用有限元模拟超浅层顶管穿越路基引起的地层移动和现场地表变形监测,研究了管道摩擦力、注浆率、顶推力、路面交通荷载等因素对覆盖土层变形的影响。研究表明：地层移动是先隆起后沉降,覆盖土层下部的移动速度比表层的大;地表变形的有限元计算结果和现场实测数据基本吻合;超浅层顶管施工对浅埋覆盖路基土层移动,横断面地表沉降变形在工具管纵向通过2倍顶管外径后基本趋于稳定,横向地表沉降沿侧向分布近似为正态分布,主要影响范围在顶管轴线左右两侧各1.5倍顶管外径的范围内;变形要求严格的地面下进行超浅层顶管施工,可以通过有限元分析对周围环境影响程度的评价。     

Effectiveness of filter gabions against slope failure due to heavy rainfall

Slope failures due to heavy rainfall events are phenomena that can cause serious damage to social infrastructures and the loss of lives. Based on previous studies, natural slope failures are generally shallow and originate at the slope toe where infiltrated rainwater has accumulated and saturated it. Hence, it is extremely important to prevent these initial failures from inducing entire slope failures. In the present study, firstly, 1 g model tests, called G series tests, were conducted. In the tests, a gabion filled with filter materials was placed at the slope toe of each model for reinforcement and to drain the accumulated rainwater from the slope toe. Filter gabions have been found to shrink the failure regions and to significantly extend the time until slope failures occur. The failure mechanism in the G series tests was almost similar to that in cases without filter gabions if focus was placed on the slope above the filter gabions. However, the drainage effect was small. Secondly, P series tests, in which a filter gabion with a pipe was introduced for each model, were conducted. The results of these tests indicated that the displacements significantly decreased as the diameter of the pipe and the depth of the pipe’s insertion to the surface layer increased. Water did not discharge through the pipe until the pore water pressure around the pipe reached positive values. The failures always started when a phreatic surface appeared on the slope surface. Thus, it is very important to prevent a phreatic surface from forming on the slope surface. The adequate arrangement of a filter gabion with a drainage pipe may increase the potential for slope stability.     

Relationship of materials in flooded soils and sediments to the water quality of reservoirs—I: Oxygen consumption rates

Rates of oxygen consumption were obtained for four soils and six reservoir sediments using sediment-water reaction chambers and a differential respirometer. Determination of microbial activity as measured by [¹⁴C]glucose metabolism was also performed on these soils and sediments. To study the transformation of newly flooded soils into aquatic sediments, we examined the effects of prolonged submergence and temperature upon oxygen consumption, carbon dioxide formation and methanogenesis. Newly flooded soils initially had high biological oxygen consumption rates, ranging from 67.2 to 76.6% of the total oxygen demand. Established reservoir sediments, in contrast, exhibited extremely high chemical oxygen demands, ranging from 62.7 to 89.9% of the total oxygen demand and had proportionately lower biological oxygen demands. Newly flooded soils had the capacity for high rates of oxygen consumption, carbon dioxide formation, and methanogenesis. However, these rates were extremely temperature-dependent and subject to rapid decline with prolonged submergence due to leaching and degradation of biologically available organic carbon (BAOC). With aging, the amount of BAOC released from the flooded soils decreased, the proportion of reduced inorganic chemical species increased, and a distinct aerobic-anaerobic double layer developed at the soil surface during aerobic conditions in the overlying water column.     

Effects of local climate and hydrological conditions on the thermal regime of a reservoir at Tropic of Cancer, in southern China

Thermal regime is strongly associated with hydrodynamics in water, and it plays an important role in the dynamics of water quality and ecosystem succession of stratified reservoirs. Changes in both climate and hydrological conditions can modify thermal regimes. Liuxihe Reservoir (23°45′50″N; 113°46′52″E) is a large, stratified and deep reservoir in Guangdong Province, located at the Tropic of Cancer of southern China. The reservoir is a warm monomictic water body with a long period of summer stratification and a short period of mixing in winter. The vertical distribution of suspended particulate material and nutrients are influenced strongly by the thermal structure and the associated flow fields. The hypolimnion becomes anoxic in the stratified period, increasing the release of nutrients from the bottom sediments. Fifty-one years of climate and reservoir operational observations are used here to show the marked changes in local climate and reservoir operational schemes. The data show increasing air temperature and more violent oscillations in inflow volumes in the last decade, while the inter-annual water level fluctuations tend to be more moderate. To quantify the effects of changes in climate and hydrological conditions on thermal structure, we used a numerical simulation model to create scenarios incorporating different air temperatures, inflow volumes, and water levels. The simulations indicate that water column stability, the duration of the mixing period, and surface and outflow temperatures are influenced by both natural factors and by anthropogenic factors such as climate change and reservoir operation schemes. Under continuous warming and more stable storage in recent years, the simulations indicate greater water column stability and increased duration of stratification, while irregular large discharge events may reduce stability and lead to early mixing in autumn. Our results strongly suggest that more attention should be focused on water quality in years of extreme climate variation and hydrological conditions, and selective withdrawal of deep water may provide an efficient means to reduce internal loading in warm years.     

微型钢管桩加固既有基础变形特性现场试验

依托河南理工大学锅炉房既有基础加固工程,优化微型钢管桩群桩加固既有基础的施工步骤,将既有灌注桩基础与柱身简化为一端固接一端简支梁模型并验证其准确性; 开展微型钢管桩加固既有基础变形特性现场试验,测得微型钢管桩群桩施工过程中既有柱子和两柱之间的地表位移以及柱子角度的变化规律,比较顺逆结合和单一逆时针群桩施工顺序对既有柱子以及地表位移的影响,探讨加固施工过程对既有上部柱子结构的变形(位移、倾角)机理。结果表明:顺逆结合的群桩施工顺序相对优于单一逆时针压桩顺序,地表位移最大值可以减少约50%,顺逆结合或单一逆时针施工顺序引起的地表位移最大值分别为既有上部柱子位移的1/6和1/4; 先施工的微型钢管桩会对周围土层产生一定的遮帘加筋作用,后施工桩朝此方向造成的土体扰动和位移相对减小,从而减小了微型钢管桩施工对既有上部柱子结构的影响; 2种施工顺序试验条件下,位移与应力最大值一般出现在第3根桩或第4根桩施工过程中。     

Seepage failure by heave in sheeted excavation pits constructed in stratified cohesionless soils

In this study, experimental and numerical investigations are performed to clarify the seepage failure by heave in sheeted excavation pits in stratified cohesionless soils in which a relatively permeable soil layer (k_upper) lies above a less permeable soil layer (k_lower) between excavation base and wall tip. It is shown that the evaluation of base stabilities of excavation pits against seepage failure by using Terzaghi and Peck’s approach leads to considerably lower critical potential differences than those obtained from the model tests. On the other hand, a relatively good agreement is achieved between the results of the model tests and the finite element (FE) analyses. Further investigations are performed by using axisymmetric excavation models with various dimensions and ground conditions, and a comparison between the results obtained from Terzaghi and Peck’s approach and finite element analyses is given.     

Stability analysis of stratified rock slopes with spatially variable strength parameters: the case of Qianjiangping landslide

Jurassic strata prone to slope failure are widely distributed in the Three Gorges Reservoir region. The limit equilibrium method is generally used to analyze the stability of rock slopes that have a single failure plane. However, the stability of a stratified rock mass cannot be accurately estimated by this method because different bedding planes have variable shear strength parameters. A modified limit equilibrium method is presented with variable water pressure and shear strength used to estimate the stability coefficient of a sloping mass of stratified rock and to identify the potential sliding surface. Furthermore, an S-curve model is used to define the spatial variations of the shear strength parameters c and ? of the bedding plane and the tensile strength of the rock mass. This model can also describe the variation of strength parameters with distance from the slope surface, which depends on the reservoir water level. Also, it is used to evaluate the stability of the Qianjiangping landslide, located at Shazhenxi Town, Zigui County, Three Gorges Reservoir area, China. The results show the most probable sliding surface is the interface between a slightly weathered layer and subjacent bedrock. When reservoir water rises above the elevation of the slide mass toe, the stability coefficient of the slope declines sharply. When the reservoir water level is static at 135 m, the stability coefficient decreases gradually as the phreatic line changes as a result of heavy rainfall.     

Daily streamflow modelling using autoregressive moving average and artificial neural networks models: case study of Çoruh basin,Turkey

Streamflow modelling is a quite important issue for water resources system planning and management projects, such as dam construction, reservoir operation and flood control. This study demonstrates the application of artificial neural networks (ANN) and autoregressive moving average (ARMA) models for modelling daily streamflow in Çoruh basin, Turkey, where there are numerous highly critical power plants either under construction or being projected. Daily streamflow records from nine gauging stations located in the basin were used in this study. In the first phase of our study, ANN and ARMA models were obtained using daily streamflow. In the second phase, 100 synthetic streamflow series were generated using previously determined ANN and ARMA models in order to ensure the preservation of main statistical characteristics of the historical time series. The results have showed that the historical time series have similar statistical parameters to those of the generated time series at 95% confidence level.     

Oxygen consumption by a sediment bed for stagnant water: comparison to SOD with fluid flow

A model of sedimentary oxygen demand (SOD) for stagnant water in a lake or a reservoir is presented. For the purposes of this paper, stagnant water is defined as the bottom layer of stratified water columns in relatively unproductive systems that are underlain by silt and sand-dominated sediments with low-organic carbon (C) and nitrogen (N). The modeling results are compared to those with fluid flow to investigate how flow over the sediment surface raises SOD compared to stagnant water, depending on flow velocity and biochemical activity in the sediment. SOD is found to be substantially limited by oxygen transfer in the water column when water is stagnant. When flow over the sediment surface is present, SOD becomes larger than that for stagnant water, depending on flow velocity and the biochemical oxygen uptake rate in the sediment. Flow over the sediment surface causes an insignificant raise in SOD when the biochemical oxygen uptake rate is small. The difference between SOD with fluid flow and SOD for stagnant water becomes significant as the biochemical oxygen uptake rate becomes larger, i.e. SOD is 10-100 times larger when flow over the sediment surface is present.     

边坡临界滑面搜索的改进粒子群优化算法

边坡临界滑面的确定对边坡稳定分析和加固设计极为重要,采用基于变异和二次序列规划的改进粒子群优化算法(VSPSO)进行临界滑面搜索。VSPSO算法中通过变异操作增强粒子群跳出局部最优解的能力,并用二次序列规划(SQP)加速局部搜索,大大提高了粒子群获得全局最优的能力。通过对有解析解的边坡算例进行分析,验证了该算法的准确性及优越性;对澳大利亚计算机应用协会(ACADS)提供的均质边坡、多层土边坡以及含软弱层边坡进行分析,结果表明改进的VSPSO算法搜索所得滑面比传统PSO算法更逼近推荐答案,具有更好的鲁棒性,而且随着边坡复杂程度的增加,更能体现改进VSPSO算法的优越性,具有广阔的应用前景。     

管壁粗糙度对室内排水立管临界流量的影响

近年来,由于建筑排水方面塑料管的推广使用,管壁粗糙度对排水立管临界流量的影响问题,引起了普遍的关注.本文通过两相流理论分析和水力学试验验证证实:室内排水立管管壁粗糙度的减小,不仅不能加大其临界流量,反而会减小其临界流量.