Numerical modelling of desiccation cracking of clayey soil using a cohesive fracture method     

《Computers and Geotechnics》2017

This paper presents a numerical study on the desiccation cracking process of clayey soil. The initiation and propagation of cracks were investigated using finite element code, including the damage-elastic cohesive fracture law to describe the behaviour of cracks. The coupling between the hydraulic behaviour (moisture transfer in the soil matrix and in the cracks) and the mechanical behaviour (volume change of the soil matrix and development of cracks) were also considered. The results of a laboratory experiment performed on clay soil, taken from a literature review, were used to evaluate the numerical modelling. The results show that the code can reproduce the main trends observed in the experiment (e.g., shrinkage related to drying, crack development). In addition, the numerical simulation enables the identification of other phenomena, such as the evolution of suction and stress related to drying and the development of a single crack. These phenomena are difficult to observe experimentally.  相似文献   

Efficiency of rainwater harvesting of microcatchments and the role of their design     

《Journal of Arid Environments》2013

Microcatchment is a technique for collecting, storing and conserving local surface runoff in order to grow trees/shrubs. In this system, runoff water is generated on a plot and stored in the soil during runoff events, and trees/shrubs may utilize this water during the next dry season.Microcatchments have relatively small runoff generation areas (from dozens to hundreds sq. m) and are cheap and simple to implement Their collection area is usually a small depression located nearby the runoff generating area in which one or a few trees/shrubs may be planted Due to the short overland flow path runoff generation is efficient and even short low intensity storms may generate runoff. The drawback is however that due to the small size of the generating area small volumes of water are conveyed to the storage plots. Another drawback is susceptibility of the augmented water to evaporation. The main objective of present research presented hereafter was to estimate the effect the depth of the depression has on the efficiency of the water conservation in the soil profile. In the present study the storage plots were circular pits and the effect their depth had on evaporative losses and water distribution were studied.The results clearly show that the depth of the pit significantly affects evaporative water losses. The losses were separately computed for the soil cylinder whose upper surface is the bottom of the pit and for the surrounding shell. No differences between treatments were evident for losses from the inner cylinder. Significant differences in water losses were however observed for the surrounding shell where the shallow pits losing as much as six times more than the deeper pits.  相似文献   

托素湖湖水蒸发过程中析盐及其pH值的变化规律研究          下载免费PDF全文

张棣  马云麒  李兴意  杨剑  彭章旷  刘玉秀  马学海 《盐湖研究》2021,29(1)

盐湖卤水蒸发是提取盐湖资源的主要途径之一,当前盐湖卤水的蒸发实验主要集中在矿化程度较高的盐湖和咸水湖中,蒸出矿物以硫酸盐和氯化物为主。为了获得湖水蒸发过程中从低矿化度到高矿化度全阶段的析盐和pH值变化规律,本文用托素湖微咸水在恒温室内开展28±2℃蒸发实验。托素湖为硫酸镁亚型微咸水湖(矿化度27.8 g/L),整个蒸发过程中pH值由8.92持续降低到6.108;矿物析出顺序为三水菱镁矿-文石-石盐-六水泻盐-白钠镁矾-五水泻盐-四水泻盐,共有七组盐类析出。卤水pH值的变化主要受矿物相变化控制,在碳酸盐析出过程中pH由8.529迅速降低到7.205,而后以析出矿物石盐为主的石盐-硫酸盐析出阶段pH降低到6.887,之后在白钠镁为主硫酸盐-石盐阶段pH缓慢降低到6.29。同时分析了石膏、芒硝、泻利盐等矿物未析出的原因。通过托素湖湖水蒸发实验,可以更全面的认识硫酸镁亚型盐湖演化全过程中的矿物沉积规律及物理化学性质变化。  相似文献   

浅海原油净化过程的模拟实验──分散油的挥发降解过程   总被引：2，自引：0，他引：2  

王永辰  祝陈坚  孙秉一  史致丽  于圣睿  郝恩良  李铁  石晓勇 《海洋与湖沼》1995,26(4):389-396

于1989年3－7月在青岛海洋大学进行“河口”原油和“东营”原油实验室模拟实验，以了解海上溢油进入海水中的分散（溶解和乳化）油的挥发降解过程。结果表明，分散油的蒸发速率除与原油本身性质有关外，还与环境温度、水体盐度和水面风速有关。水体中油含量随时间变化可表示为：，温度、盐度和风速增大时，均有助于分散油的挥发，其中风速变化对Kv的影响最大，而盐度变化的影响最小。  相似文献   

Boron isotopic fractionation during seawater evaporation   总被引：6，自引：0，他引：6  

Y.K. Xiao  S.Z. Li  H.Z. Wei  A.D. Sun  W.G. Liu  W.J. Zhou  Z.Q. Zhao  C.Q. Liu  G.H. Swihart 《Marine Chemistry》2007,103(3-4):382-392

Laboratory experiments were undertaken to investigate the behaviour of boron at the seawater–air interface during seawater evaporation. Seawaters adjusted to different pH values were heated to 27, 33 and 40 °C inside a quartz evaporator. The vapor was collected with a quartz condenser using a cold trap. A natural seawater–vapor process in quiet air conditions and excluding the sea-spray component was realized using this arrangement. The results indicate an enrichment of ¹¹B in the condensate. This implies that in the natural environment, rainfall with δ¹¹B values lower than that of seawater has been affected either by continental boron sources or by the boron extracted from seawater under airflow conditions. While the net flux of boron carried away from the ocean by air masses due to seawater evaporation is significant compared to other fractionation-associated processes removing boron from the ocean, the effect of isotopic fractionation as boron enters the vapor phase on the isotopic composition of boron in the ocean over time is small.  相似文献   

多种水面类型蒸发的研究   总被引：1，自引：0，他引：1  

毛锐  高俊峰 《海洋与湖沼》1996,27(4):445-450

分析有水草水面、污水面、受热水面、盐水（盐水）面等特定水面类型的蒸发量，并与清水、淡水对照，求出蒸发比，还计算了太湖地区有水草水面和受热水面的蒸发模型，为确定湖泊的蒸发量提供一新途径，最后建议用水生植物的蒸腾规律来控制水面蒸发，调节水面温度。  相似文献   

Salt crystallization in pores: quantification and estimation of damage     

Matthieu?AngeliEmail author  Jean-Philippe?Bigas  David?Benavente  Beatriz?Menéndez  Ronan?Hébert  Christian?David 《Environmental Geology》2007,52(2):205-213

The objective of this study is to understand and predict the alteration of porous rock by crystallization of salts. Samples of different rocks have been tested according to the EN 12370 standard test. Two parameters are proposed to evaluate the alteration of a rock during these tests. The alteration index AI represents the cycle in which the first damages occur. The alteration velocity AV represents the alteration rate at the end of the experiment, when the decay has become regular. These parameters can be estimated with the help of a microstructural study of the rocks. The most relevant intrinsic parameters of the stones for this estimation are capillary coefficient, evaporation coefficient, tensile strength and P-waves velocity. An evaluation of the alteration pattern is also proposed depending on the eventual heterogeneities and anisotropies of the rocks. The influence of the dimension and shape of the samples is also discussed.  相似文献   

Anisotropy of Mg isotopic fractionation during evaporation and Mg self-diffusion of forsterite in vacuum     

Maho Yamada  Shogo Tachibana  Hiroko Nagahara  Kazuhito Ozawa 《Planetary and Space Science》2006,54(11):1096-1106

Evaporation of solid materials under low-pressure conditions could play important roles in chemical and isotopic fractionations in the early solar system. We have studied anisotropy of isotopic fractionation of ²⁶Mg and ²⁵Mg during kinetic evaporation of forsterite (Mg₂SiO₄), which is potentially a powerful tool to understand thermal histories of crystals in the early solar system. Ion-microprobe depth profiling revealed that the Mg isotopic zoning profiles of forsterite evaporated at 1500-1700 °C are notably differing along the a-, b-, and c-axes, which can be attributed to anisotropy in self-diffusion coefficient of Mg (D) and an isotopic fractionation factor for evaporation of Mg (α). The D and α were obtained from zoning profiles by applying the diffusion-controlled isotopic fractionation model of Wang et al. [1999. Evaporation of single crystal forsterite: Evaporation kinetics, magnesium isotope fractionation, and implications of mass-dependent isotopic fractionation of a diffusion-controlled reservoir. Geochim. Cosmochim. Acta 63(6), 953-966.].The D is largest and smallest along the a- and c-axes, respectively. The activation energy of 560-670 kJ/mol indicates that Mg diffusion at 1500-1700 °C occurred in the intrinsic diffusion regime.The α seems to be larger along the a- or c-axes than along the b-axis. The α along the a- or c-axes show weak temperature dependence. The α along all the crystallographic orientations is closer to unity than that expected from the kinetic theory of gases. These lines of evidence suggest that surface processes such as breaking of bonds and surface diffusion are responsible for the isotopic fractionation.  相似文献   

Modelling of evaporation in a sparse millet crop using a two-source model including sensible heat advection within the canopy     

M. R. Lund  H. Soegaard 《Journal of Hydrology》2003,280(1-4):124-144

During two successive growing seasons meteorological measurements were made in a pearl millet field in the Sahel to investigate the evaporation process in relation to crop growth. The evaporation was measured by eddy correlation and simulated using the Shuttleworth Wallace (SW) model [Q. J. R. Meteorol. Soc. 111 (1985) 839–855]. To take sun height and multi-layer scattering into account a radiation balance model was formulated. The model indicates that partitioning of the net radiation between the vegetation and the soil may be estimated (r²=0.94) from the fraction of diffuse radiation, the leaf area index and an attenuation coefficient, but that the attenuation coefficient may not be similar in different locations. To solve the SW-model with respect to the soil resistance an iterative solution was employed with the total evaporation estimated from the Bowen-ratio calculated from eddy correlation measurements. The procedure made it possible to derive stable estimates of soil resistance at soil evaporation rates down to 25 W m⁻². The soil resistance was found to be in accordance with evaporation through a dry surface layer. The SW-model indicates, that advection of sensible heat from the dry soil to the plants, increases transpiration considerably. This will cause management techniques, such as mulching and dry farming, aimed at reducing soil evaporation to be less effective than might be anticipated. The effects of raising the leaf area index to improve the microclimate is discussed in relation to management of the available water and crop security.  相似文献   

Evaluating a Model of Evaporation and Transpiration with Observations in a Partially Wet Douglas-Fir Forest   总被引：1，自引：0，他引：1  

Fred C. Bosveld  Willem Bouten 《Boundary-Layer Meteorology》2003,108(3):365-396

The Penman–Monteith equation is extended to describe evaporation of intercepted rain, transpiration and the interaction between these processes in a single explicit function. This single-layer model simulates the effects of heat exchange, stomatal blocking and changed humidity deficit close to the canopy as a function of canopywater storage. Evaporation depends on the distribution of water over the canopy and the energy exchange between wet and dry parts. Transpiration depends on the dry canopy surface resistance that is described with a Jarvis-type response. The explicit functions obtained for water vapour fluxes facilitate a straightforward identificationof the various processes. Canopy water storage amounts and xylem sapflow were measured simultaneously during drying episodes after rainfall in a dense, partially wet, Douglas-fir forest. Estimates of evaporation and transpiration rates are derived from these observations. The analysis shows that evaporation induced transpirationreduction is mainly caused by energy consumption. Changes in water vapour deficit have a minor effect due to a compensating stomatal reaction. The remaining difference between observed and modelled transpiration reduction can be attributed to partial blocking of stomata by the water layer.  相似文献