浅谈井点降水施工技术

在地下水位较高的地方开挖深基坑,如不降水,会造成基坑浸水,使施工条件变差及地基承载力下降;因此,基坑降水排水是基础施工中的一项重要技术措施。     

水利工程基坑排水施工技术

从地基土质分类、基坑降水方案设计、排水施工、开挖排水沟、集水井或井管施工需注意的问题等方面对水利工程基坑排水施工技术进行了分析研究。     

城市井点降水施工实践与应用

随着高层建筑的不断增加,在城区施工采用井点降水,引起邻近建筑、管线、路面开裂下沉的现象屡见不鲜.因此,采用井点降水要特别慎重并采取相应对策.     

市政工程施工气象条件及气象指数分析研究

对池州市降水、温度、降雪和风等气象因子与市政工程施工的影响关系进行了分析,以找出不利的气象因素影响工程质量和施工安全.通过季节性气象特征分析,得出了雨季(5月～8月)和冬季(11月～翌年2月)是市政工程施工质量控制的关键阶段,而3～5月、8～11月气候是市政工程施工最佳时间段.通过建立市政工程施工气象指数,对相关气象因...     

人工挖孔扩底灌注桩遇水施工的处理

大孔经人工挖孔扩底灌注遇地下水施工难度大,本工程采用大管井降水,钢护筒,伞模护壁等工艺和技术解决了这一难题。     

软土地层地铁隧道施工对地下管线的影响分析

指出了在软土地层中进行地铁隧道施工必然会出现地表沉降,对现有地下线管产生影响。针对建设效应与流固耦合效应进行了深入分析,并且在线管规定的安全控制范围之中,借助FLAC工具创建了科学的数据模型,通过对比结果可看出,对地层固结沉降变形起到最大作用的是非降水施工法,某市轨道交通1号线通过使用此方法,确保了煤气线管在施工期间的安全和正常使用。     

SWAN定量降水预报产品在宝鸡汛期短时降水的检验应用

选取2015年汛期宝鸡典型的三类降水过程,采用宝鸡市区域站和自动站雨量以及SWAN定量降水预报产品资料,用点对点统计检验评分方法,分析了SWAN系统中定量降水预报产品在宝鸡不同类型降水过程中的准确率和误差分布。结果表明:同一预报时效下,QPF产品对层状云降水的预报效果最好,其次是积状云,层积混合预报效果最差;随着降水的加强,不同预报时效误差不同,预报时效越长,误差越大,三种类型降水过程均是如此。相对误差则是层积混合型降水最小,积状云降水最大,绝对误差层状云降水最小,层积混合型降水最大;层状云降水总体分布为东部大西部小,积状云降水总体分布为西南—东北走向,依次朝西北和东南减小,层积混合类型降水过程中,30min预报时效下绝对误差大值中心位于陈仓,麟游和凤县绝对误差最小,60min预报时效下绝对误差分布特征为东部大西部小,由东向西依次减小。     

高寒林区公路圆管涵使用中的问题及防护

圆管涵因其施工方便，造价低，节省材料，被林区公路广泛采用。大兴安岭属多年冻土地区，由于受气候、降水、冻土等因素的影响，公路管涵受损十分普遍。据调查，大兴安岭林区公路修建的管涵６０％以上存在着不同程度的损坏，一些已丧失原有功能。由于管涵受损较多，修复困...     

塞罕坝林区的降水与造林生产的关系

塞罕坝1960－1980年同一等级降水量呈现隔年的规律，由于森林环境的逐渐形成，1981－2000年同一等级降水主要呈现连年规律，提出了降水与要成活率的关系。通过对年降水量的分析，揭示了不同时空降水的比重和不平衡性；4－5月份降水50mm，可作为造林成活的基本指标，6月份的降水连续起着重要作用，7－9月降水比重占60.77%。年降水天数至少增加23d。根据降水规律和对应于造林成活率的分析，结合实践经验，提出了3项有利于造林和成活的措施建议。     

降水在沙丘中的渗透过程研究

观测研究结果表明 :⑴降水在沙丘上下渗深度与降水量及降水强度成正相关 ,与气温成负相关。民勤沙区雨季降水量在 4 0mm以上时在沙丘中的下渗深度可以达到 5 0～ 90cm。在当地 ,秋季降水尤其是秋季连续降水是沙丘储存水分的主要来源。⑵降水在沙丘上的下渗速率与降水量正相关 ,降水量大 ,主要含水层的含水率则高 ,下渗速度自然就快。⑶降水后梭梭根部沙面 0～ 5cm含水率高于流动沙丘 ;降水停止 1d以后对应于流动沙丘的最大含水层梭梭根部的含水率明显降低 ;降水停止 1d后在流动沙丘降水下渗深度内的平均含水率高于梭梭沙丘对应层含水率 ,且随时间推移这个差值在增大。⑷在 0～ 4 5mm的降水量范围内 ,不论是流动沙丘还是有梭梭林的沙丘 ,其降水的主要含水层在表层 0～ 2 0cm范围内。⑸当地 8月上旬 <12mm的降水量在降水停止后的 7～ 8d内蒸发殆尽 ;4 3.5mm的降水量在降水停止后第 10天时 0～ 15 0cm沙层含水率折合水层深度较降水前多 17.2 8mm ;2 1.7mm的降水量在降水停止后第 10天时 0～ 15 0cm沙层含水率折合水层深度较降水前多 10 .6 6mm ;在降水过程中和降水后的 1d内水分蒸发损耗最大     

Modeling the process of absorption and desorption of water above and below the fiber saturation point

Summary The process of absorption of water along the tangential direction of the wood is studied by immersing the sample in water. The transport of water is then obtained below the fiber saturation point at the beginning of the absorption and above this fiber saturation point during the process. The potential which drives the transport of the bound-water and free-water through the wood has been considered by testing a diffusional transport model. The transient diffusion with a constant diffusivity has been found to describe not only the process of absorption but also the process of desorption with diffusion of water through the solid and evaporation from the surface. Analytical solutions have been successfully used to describe the stage of absorption during a time of four hours at the end of which an equilibrium of absorption is attained, as well as the following stage of desorption. A model based on a numerical method with finite differences has been found to describe the process of absorption and desorption in various cases, and especially when the equilibrium of absorption has not been attained.This work was carried out with the help and support of the M. R. T. and the French CTB (Wood Technical Center)     

Theoretical water sorption energies by conformational analysis

Summary Values of the sorption energies of single molecules of water on all available sorption sites of amorphous cellulose I have been obtained by conformational analysis. The sorption energies are equated to the total energy (Etot) of interaction between the water molecule and all the atomic groups of the cellulose. Van der Waal, H-bond and electrostatic energies comprised the E_tot. The interference of water molecules on two vicinal sorption sites were also obtained and sites in which such interference can occur were identified for amorphous cellulose. Curves relating E_tot to percentage equilibrium moisture content are reported as well as exact sorption isotherms constructed as E_tot as a function of humidity for the amorphous and crystalline cellulose I. These isotherms were constructed for different relative proportions of amorphous to crystalline cellulose and can be constructed for any of their relative proportions from the isotherms for amorphous-only and crystalline-only cellulose. The sorption energies of the monolayer were all calculated. Curves of energy of sorption of bound water were also obtained by introducing the calculated energy values in equations from already established sorption theories.Sorption capacities of amorphous and crystalline Cellulose I were calculated and the respective isotherms constructed and discussed from the point of view of existing sorption theories.     

Leaf water relations of Eucalyptus cloeziana and Eucalyptus argophloia in response to water deficit

Leaf water relations responses to limited water supply were determined in 7-month-old plants of a dry inland provenance of Eucalyptus argophloia Blakely and in a humid coastal provenance (Gympie) and a dry inland provenance (Hungry Hills) of Eucalyptus cloeziana F. Muell. Each provenance of E. cloeziana exhibited a lower relative water content at the turgor loss point, a lower apoplastic water content, a smaller ratio of dry mass to turgid mass and a lower bulk modulus of elasticity than the single provenance of E. argophloia. Osmotic potential at full turgor and water potential at the turgor loss point were significantly lower in E. argophloia and the inland provenance of E. cloeziana than in the coastal provenance of E. cloeziana. There was limited osmotic adjustment in response to soil drying in E. cloeziana, but not in E. argophloia. Between-species differences in water relations parameters were larger than those between the E. cloeziana provenances. Both E. cloeziana provenances maintained turgor under moderate water stress through a combination of osmotic and elastic adjustments. Eucalyptus argophloia had more rigid cell walls and reached lower water potentials with less reduction in relative water content than either of the E. cloeziana provenances, thereby enabling it to extract water from dryer soils.     

A NMR study of water distribution in hardwoods at several equilibrium moisture contents

The water state of one tropical (Robinia coccinea) and two temperate (Acer saccharum and Fagus grandifolia) hardwoods was determined at different equilibrium moisture contents (EMC) during desorption at 25°C. NMR technique was used to separate different components of water in wood. The species studied presented different structures, which were apparent on the spin–spin relaxation T₂ values. Three different water components were separated: slow T₂ (liquid water in vessel elements), medium T₂ (liquid water in fiber and parenchyma elements) and fast T₂ (bound or cell wall water). The NMR results showed that even at equilibrated conditions a region exists where loss of liquid water and bound water takes place simultaneously. This region will vary according to the wood structure. Finally, liquid water was present at EMC lower than the fiber saturation point, which contradicts the concept of this point when considered as a bulk property of wood.     

Variation analysis of growth traits of four poplar clones under different water and fertilizer management

To determine appropriate quantities of water and fertilizer required for early growth of hybrid poplar cuttings,we recorded the growth traits of four clones grown under four factors(irrigation and nitrogen,phosphorus,and potassium fertilizers),each with four levels,using an orthogonal experimental design.A logistic model was used to estimate growth in height.The growth curves for tree height were sigmoid,and the model R^2 values were greater than 0.9,which indicated that the fit was highly significant.ANOVA results for tree height and basal diameter indicated that all sources of variance showed significant differences(p<0.001).The average tree height and basal diameter for all the four clones under the different treatments ranged from 155.39 to 235.04 cm,and from 13.71 to 17.42 mm,respectively.A highly positive correlation between the extreme k value and tree height was observed,suggesting that the k value was an accurate estimation of tree height.For model parameters,the earliest average time point for the onset of the rapid growth period of poplar clones was 131 d,and the highest average increment in tree height during the rapid growth period was 138.78 cm.The highest average tree height for all clones under each factor was 219,210.51,200,and 201 cm when treated with either 1200 mL of water applied every third day,3 g of nitrogen,0 g of phosphorus,or 0 g of potassium,respectively.The most suitable treatment for the early growth of hybrid poplar cuttings,as suggested by the developed logistic model,was 1200 mL of water applied every third day and three applications of 1 g nitrogen(in the form of CH4N2O).     

Growth, leaf morphology, water use and tissue water relations of Eucalyptus globulus clones in response to water deficit

Changes in leaf size, specific leaf area (SLA), transpiration and tissue water relations were studied in leaves of rooted cuttings of selected clones of Eucalyptus globulus Labill. subjected to well-watered or drought conditions in a greenhouse. Significant differences between clones were found in leaf expansion and transpiration. There was a significant clone x treatment interaction on SLA. Water stress significantly reduced osmotic potential at the turgor loss point (Pi0) and at full turgor (Pi100), and significantly increased relative water content at the turgor loss point and maximum bulk elastic modulus. Differences in tissue water relations between clones were significant only in the mild drought treatment. Among clones in the drought treatments, the highest leaf expansion and the highest increase in transpiration during the experiment were measured in those clones that showed an early and large decrease in Pi0 and Pi100.     

Soil water response to precipitation in different microtopographies on the semi-arid Loess Plateau,China

Soil water is an important factor restricting afforestation on the semi-arid Loess Plateau.The microtopography of the loess slope has changed the distribution pattern of soil water on the slope.To improve water utilization efficiency and optimize afforestation configuration patterns,the relationship between soil water and precipitation at micro-topographic scale must be studied.We used time series analysis to study the temporal variation of soil water and its response to precipitation in four kinds of micro-topographies and undisturbed slope on loess slopes.Micro-topographies significantly influenced soil water distribution and dynamics on the slopes.Soil water stored in the platform,sinkhole,and ephemeral gully influenced subsequent soil water for 4 weeks,whereas soil water stored in the scarp and undisturbed slope could influence soil water for 2 weeks.It took 12 weeks,10 weeks,18 weeks,6 weeks,and 12 weeks for precipitation to reach the deeper soil layer in the platform,sinkhole,scarp,ephemeral gully,and undisturbed slope,respectively.These soil water characteristics in different micro-topographies are vital factors that should be taken into consideration when undertaking afforestation on the Loess Plateau.     

The effect of openings on combined bound water and water vapor diffusion in wood

This study was undertaken to estimate the effect of openings between cell walls on combined bound water and water vapor diffusion in wood. Using a newly developed model, the radial and tangential moisture diffusion coefficients can be predicted depending on the opening area. The new model explicitly involves a term for water vapor diffusion through the openings, as well as a term for the combined diffusion of bound water and water vapor. A classical model developed by Stamm and Choong had higher longitudinal moisture diffusion coefficients than that in the parallel model at higher moisture content, which is inconsistent with the Wiener bound rule. The new model suggested in this article is useful for analyzing the experimental results and understanding the variability of the diffusion coefficients.     

Interaction of ozone with simultaneous water deficit and water deficit preconditioning in one-year-oldPinus densiflora seedlings

The primary objective of this study was to investigate if responses of pottedPinus densiflora Sieb. et Zucc. seedlings to ozone exposure could be altered by water deficit stress applied before or during ozone exposure. One-year-old seedlings grown from seeds in pots were used. Water deficit preconditioning was done for ten weeks from May 1, 1998, followed by ozone exposure and simultaneous water deficit for eight weeks. Water deficit was controlled by monitoring xylem water potentials with a pressure chamber. Ozone was fumigated in open top chambers with an eight-hour mean concentration of 0.1 ppm. A 2³ factorial design was employed. Dry weights, carbohydrate concentrations, and leaf gas exchanges were measured. In response to the water deficit, growth and stomatal conductance were reduced, while soluble carbohydrate concentrations were enhanced. Interactions between ozone and simultaneous water deficit were significant. Dry weights were significantly decreased by ozone exposure only in well-watered seedlings, suggesting that simultaneous water deficit may alleviate the adverse effects of ozone. This protection from ozone stress observed in water-stressed seedlings resulted from: (1) reduced ozone uptake due to stomatal closure and (2) enhanced TNC (Total Nonstructural Carbohydrates) which acted as a buffer against ozone injury.     

Drought resistance of Ailanthus altissima: root hydraulics and water relations

Drought resistance of Ailanthus altissima (Mill.) Swingle is a major factor underlying the impressively wide expansion of this species in Europe and North America. We studied the specific mechanism used by A. altissima to withstand drought by subjecting potted seedlings to four irrigation regimes. At the end of the 13-week treatment period, soil water potential was -0.05 MPa for well-watered control seedlings (W) and -0.4, -0.8 and -1.7 MPa for drought-stressed seedlings (S) in irrigation regimes S1, S2 and S3, respectively. Root and shoot biomass production did not differ significantly among the four groups. A progressively marked stomatal closure was observed in drought-stressed seedlings, leading to homeostasis of leaf water potential, which was maintained well above the turgor loss point. Root and shoot hydraulics were measured with a high-pressure flow meter. When scaled by leaf surface area, shoot hydraulic conductance did not differ among the treated seedlings, whereas root hydraulic conductance decreased by about 20% in S1 and S2 seedlings and by about 70% in S3 seedlings, with respect to the well-watered control value. Similar differences were observed when root hydraulic conductance was scaled by root surface area, suggesting that roots had become less permeable to water. Anatomical observations of root cross sections revealed that S3 seedlings had shrunken cortical cells and a multilayer endodermal-like tissue that probably impaired soil-to-root stele water transport. We conclude that A. altissima seedlings are able to withstand drought by employing a highly effective water-saving mechanism that involves reduced water loss by leaves and reduced root hydraulic conductance. This water-saving mechanism helps explain how A. altissima successfully competes with native vegetation.