A generalized transformation approach for simulating steady-state variably-saturated subsurface flow     

Sung-Hoon Ji  Young-Jin Park  Edward A. Sudicky  Jon F. Sykes 《Advances in water resources》2008

A numerical method is proposed to accurately and efficiently compute a direct steady-state solution of the nonlinear Richards equation. In the proposed method, the Kirchhoff integral transformation and a complementary transformation are applied to the governing equation in order to separate the nonlinear hyperbolic characteristic from the linear parabolic part. The separation allows the transformed governing equation to be applied to partially- to fully-saturated systems with arbitrary constitutive relations between primary (pressure head) and secondary variables (relative permeability). The transformed governing equation is then discretized with control volume finite difference/finite element approximations, followed by inverse transformation. The approach is compared to analytical and other numerical approaches for variably-saturated flow in 1-D and 3-D domains. The results clearly demonstrate that the approach is not only more computationally efficient but also more accurate than traditional numerical solutions. The approach is also applied to an example flow problem involving a regional-scale variably-saturated heterogeneous system, where the vadose zone is up to 1 km thick. The performance, stability, and effectiveness of the transform approach is exemplified for this complex heterogeneous example, which is typical of many problems encountered in the field. It is shown that computational performance can be enhanced by several orders of magnitude with the described integral transformation approach.  相似文献   

Reactive transport in unsaturated soil: Comprehensive modelling of the dynamic spatial and temporal mass balance of water and chemical components     

L. Wissmeier  D.A. Barry 《Advances in water resources》2008

By implementing the moisture-based form of Richards’ equation into the geochemical modelling framework PHREEQC, a generic tool for the simulation of one-dimensional flow and solute transport in the vadose zone undergoing complex geochemical reactions was developed. A second-order, cell-centred, explicit finite difference scheme was employed for the numerical solution of the partial differential equations of flow and transport. In this scheme, the charge-balanced soil solution is treated as an assembly of elements, where changes in water and solute contents result from fluxes of elements across cell boundaries. Therefore, water flow is considered in terms of oxygen and hydrogen transport.  相似文献   

Reprint of “Multi-step and two-step experiments in heterogeneous porous media to evaluate the relevance of dynamic effects”     

H.-J. Vogel  A. Samouëlian  O. Ippisch 《Advances in water resources》2008

The determination of hydraulic properties in non-stationary experiments is suspected to be affected by dynamic effects. This is based on thermodynamic considerations on the pore scale displacement of wetting and non-wetting phase. But also macroscopic heterogeneities at the continuum scale may influence the dynamics of water during drainage and wetting. In this paper we investigate both aspects. Firstly, we present the results of typical multi-step outflow experiments in heterogeneous sand columns which are compared with two-step outflow experiments covering the same pressure range. The discrepancies caused by pressure steps of different size reveal the impact of dynamic effects due to the non-stationarity of the experiments.  相似文献   

Unconventional Energy Resources: 2007–2008 Review     

American Association of Petroleum Geologists  Energy Minerals Division 《Natural Resources Research》2009,18(2):65-83

This paper summarizes five 2007–2008 resource commodity committee reports prepared by the Energy Minerals Division (EMD) of the American Association of Petroleum Geologists. Current United States and global research and development activities related to gas hydrates, gas shales, geothermal resources, oil sands, and uranium resources are included in this review. These commodity reports were written to advise EMD leadership and membership of the current status of research and development of unconventional energy resources. Unconventional energy resources are defined as those resources other than conventional oil and natural gas that typically occur in sandstone and carbonate rocks. Gas hydrate resources are potentially enormous; however, production technologies are still under development. Gas shale, geothermal, oil sand, and uranium resources are now increasing targets of exploration and development, and are rapidly becoming important energy resources that will continue to be developed in the future.

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干砂强夯动力特性的细观颗粒流分析   总被引：5，自引：0，他引：5  

贾敏才  王磊  周健 《岩土力学》2009,30(4):871-878

通过引进和开发二维颗粒流程序,基于相似理论建立了可以模拟砂土地基强夯加固的细观颗粒流模型,结合小比尺室内细观模型试验,从颗粒细观力学角度入手对干砂在强夯冲击加固过程中的动力反应特性进行了数值模拟。结果表明,数值模拟结果与试验结果有较好的一致性,利用颗粒流模型可以很好地模拟干砂在冲击荷载作用下的锤底动接触应力、颗粒间动接触应力和颗粒位移场分布情况,并可以实时跟踪颗粒的变位及接触应力变化,实现从细观角度揭示干砂强夯动力响应特性,研究工作为今后砂土强夯加固宏细观机制研究提供了一条新的思路。  相似文献   

钙质石灰岩中桩基轴向承载特性的有限元分析   总被引：1，自引：0，他引：1  

彭芳乐  高伟  清住真  大内正敏 《岩土力学》2009,30(9):2792-2798

为了研究钙质石灰岩中桩基的合理设计理论及开发相关的变形破坏数值分析方法,利用弹塑性有限元方法对以硫球石灰岩作为持力层的桩基现场轴向载荷试验进行了数值分析。有限元分析中钙质石灰岩被假定为理想弹塑性材料。结果表明,如果能在有限元解析中合理地考虑桩侧摩阻力的低减效果,弹塑性有限元计算可以较好地模拟与分析钙质砂土中桩基的轴向承载力特性。最后还对开口钢管桩基的土塞效应的发生机制进行了分析。  相似文献   

石佛寺水库改性粉细砂筑坝试验研究     

张丽娟  韩江 《岩土力学》2005,26(11):1866-1868

采用室内试验和现场原型试验,对辽河石佛寺水库库区内掺入水泥后粉细砂的特性进行了研究。试验结果表明,随着水泥掺入量的增加,粉细砂的凝聚力和内摩擦角增大,渗透系数减小。当水泥的掺入量为2 % 时,抗剪强度指标和渗透系数已明显改善,而且在最不利的情况下满足对渗透变形的要求。粉细砂掺入水泥后,其性能得到了很大改善,用于修筑拦河主坝是完全可行的。  相似文献   

Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA   总被引：1，自引：0，他引：1  

Joseph L. Domagalski  Steven P. Phillips  E. Randall Bayless  Celia Zamora  Carol Kendall  Richard A. WildmanJr  Janet G. Hering 《Hydrogeology Journal》2008,16(4):675-690

Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N₂ in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.  相似文献   

The consolidation characteristics of an unsaturated compacted soil   总被引：2，自引：1，他引：1  

C. Kayadelen 《Environmental Geology》2008,54(2):325-334

The compacted soils are extensively employed as mineral liners or a sealing system, constructed under municipal solid waste and other containment hazardous materials to prevent or minimize the leakage of pollutant liquids and gases into ground water and sublayers. This article presents a detailed experimental study on settlement characteristics, which are required for the construction of a sealing system. For the experimental study where a compacted unsaturated soil taken from Adana in Turkey has been used, a special equipped consolidation cell has been designed and constructed. The matric suction adopted as independent stress-state variables has been controlled by using the axis translation technique. The consolidation tests have been performed under constant matric suction. Furthermore, the pressure plate tests for various net vertical stresses have been conducted. The test results have indicated that the settlement characteristics of a compacted soil as mineral liners and covers are highly affected by matric suction. The water retention capacity of mineral liners, an important factor for hydraulic conductivity, also changes with the vertical load. The compressibility decreases as the matric suction increases. It has been observed that there exists an exponential relationship between the compressive indexes (C _t, D _t) and matric suction.  相似文献   

青藏高原中部扎布耶茶卡142 ka以来石英砂表面特征及环境意义   总被引：4，自引：1，他引：3  

李明慧  康世昌  郑绵平 《冰川冻土》2008,30(1):125-131

石英抗风化能力强,表面特征保留了许多环境信息,用扫描电镜方法对石英砂表面结构进行了研究.结果表明: 扎布耶茶卡的石英颗粒以次棱角状、次圆状为主,撞击坑、贝壳状断口、平行解理和水下磨光面等机械特征出现频率较高;化学特征有二氧化硅沉淀、蜂窝状溶蚀面、硅质球和蚀坑/洞.石英颗粒经历冲洪积作用,搬运至湖泊后又经历了水下机械和化学作用.在142～60 ka BP扎布耶茶卡湖区气候寒冷,但无冰川作用存在,石英颗粒搬运距离近,机械特征主要是强烈的物理风化与冲洪积作用形成的,化学特征与弱的水动力条件有关;8.5～3.7 ka BP湖区气候温暖,但变化频繁,湖水进一步咸化、退缩,山坡后退变缓,机械特征主要由物理风化及搬运中的碰撞造成,化学特征则与弱的水动力条件和高盐环境有关.  相似文献