挥发性有机物污染土壤工程修复技术研究进展

在论述挥发性有机物污染土壤的特性基础上,着重回顾了此类污染土壤的工程修复技术的研究进展,并重点介绍适用于挥发性有机物污染土壤治理的热解吸、光降解、土壤淋洗和土壤气相抽提等工程修复技术的应用及其影响因素,为我国今后开展类似工作提供了技术借鉴。     

Inter‐particle contact heat transfer in soil systems at moderate temperatures

An inter‐particle contact heat transfer model for evaluating soil thermal conductivity is analysed with respect to soils, representing different textural classes, exposed to moderate temperatures ranging from 15 to 30°C. This model is a combination of a self‐consistent approximation model, enhanced with an inter‐particle contact heat transfer correction coefficient. For dry and saturated soils, this coefficient is defined as a ratio of a soil harmonic mean thermal conductivity of solid and fluid (air or water) phases, to the average thermal conductivity of soil solid grains. For unsaturated soils, we assume a linear interpolation of the correction coefficient between absolutely dry and saturated states, with a Kersten function (Ke) as a proportional factor. The strongest impact of the correction coefficient (maximum reduction of heat transfer) is observed for coarse soils below a critical value of saturation degree (S_r‐cr–corresponds to Ke?0) followed by medium and fine soils. For S_r>S_rcr, the reduction of heat transfer gradually diminishes as S_r approaches 1 (i.e. saturated state). Soil texture, soil specific surface area, porosity and mineralogical composition (particularly quartz content) are important factors influencing the heat transfer correction coefficient. Their influence appears to be more substantial at the lower half of the wetness range (S_r<0.5). Simulation results from the new enhanced model closely follow experimental data.     

Evaluation of Multidimensional Transport through a Field-Scale Compacted Soil Liner

A field-scale compacted soil liner was constructed at the University of Illinois at Urbana-Champaign by the U.S. Environmental Protection Agency (USEPA) and Illinois State Geological Survey in 1988 to investigate chemical transport rates through low permeability compacted clay liners (CCLs). Four tracers (bromide and three benzoic acid tracers) were each added to one of four large ring infiltrometers (LRIs) while tritium was added to the pond water (excluding the infiltrometers). Results from the long-term transport of Br? from the localized source zone of LRI are presented in this paper. Core samples were taken radially outward from the center of the Br? LRI and concentration depth profiles were obtained. Transport properties were evaluated using an axially symmetric transport model. Results indicate that (1) transport was diffusion controlled; (2) transport due to advection was negligible and well within the regulatory limits of ksat ? 1×10?7?cm/s; (3) diffusion rates in the horizontal and vertical directions were the same; and (4) small positioning errors due to compression during soil sampling did not affect the best fit advection and diffusion values. The best-fit diffusion coefficient for bromide was equal to the molecular diffusion coefficient multiplied by a tortuosity factor of 0.27, which is within 8% of the tortuosity factor (0.25) found in a related study where tritium transport through the same liner was evaluated. This suggests that the governing mechanisms for the transport of tritium and bromide through the CCL were similar. These results are significant because they address transport through a composite liner from a localized source zone which occurs when defects or punctures in the geomembrane of a composite system are present.     

Evaluation of Cone Penetration Test-Based Settlement Prediction Methods for Shallow Foundations on Cohesionless Soils at Highway Bridge Construction Sites

The cone penetration test (CPT) method is gaining popularity in the United States as one of the premier subsurface exploration techniques. The writers previously monitored settlement behavior of spread footing foundations at five highway bridge construction sites in Ohio and evaluated the standard penetration test-based settlement prediction methods in light of the field performance data. The authors recently conducted CPT sounding at these bridge sites. In this paper, settlement behavior of five spread footings resting on cohesionless soils at two sites were predicted with the CPT-based settlement prediction methods proposed by Amar, DeBeer, Meyerhof, and Schmertmann. The results showed that the prediction methods by Schmertmann and DeBeer were both conservative but reasonably reliable in predicting the settlement of shallow foundations observed in the field.     

Cation exchange capacity methodology III: Correct exchangeable calcium determination of calcareous clays using a new silver–thiourea method

Cation exchange capacity (CEC) is a fundamental property of clays and soils. Determination of CEC for samples that contain Ca-carbonate minerals, such as calcite and dolomite, is problematic because Ca²⁺ released by dissolution of carbonates during CEC determinations interferes with the accuracy of CEC values. This paper describes a new method for the determination of correct exchangeable Ca²⁺ values of calcareous clays and soils. For the method, a silver–thiourea exchange solution is saturated with Ca²⁺ by treatment with fine-grained calcite prior to the start of the exchange procedure. Using this exchange solution, calcite in the sample can no longer be dissolved but exchangeable Ca²⁺ is desorbed quantitatively. The case for dolomite is similar, because dissolution of dolomite is minimised. However, the determination of reasonable exchangeable Ca²⁺ values for samples containing gypsum is not possible because gypsum is soluble in the exchange solution.     

Differentiation in the fertility of Inceptisols as related to land use in the upper Solimões river region, western Amazon

The Upper Solimões river region, western Amazon, is the homeland of indigenous populations and contains small-scale agricultural systems that are important for biodiversity conservation. Although traditional slash-and-burn agriculture is being practiced over many years, deforestation there is relatively small compared to other Amazon regions. Pastures are restricted to the vicinity of cities and do not spread to the small communities along the river. Inceptisols are the main soil order (>90%) in the area and have unique attributes including high Al content and high cation exchange capacity (CEC) due to the enrichment of the clay fraction with 2:1 secondary aluminosilicates. Despite its importance, few studies have focussed on this soil order when considering land use effects on the fertility of Amazon soils. Thus, the objective of this study was to evaluate changes in soil fertility of representative land use systems (LUSs) in the Upper Solimões region, namely: primary rainforest, old secondary forest, young secondary forest, agroforestry, pasture and agriculture. LUSs were significantly differentiated by the chemical attributes of their topsoil (0-20 cm). Secondary forests presented soil chemical attributes more similar to primary rainforest areas, while pastures exhibited the highest dissimilarity from all the other LUSs. As a whole, soil chemical changes among Inceptisols dominated LUSs showed patterns that were distinct from those reported from other Amazon soils like Oxisols and Ultisols. This is probably related to the presence of high-activity clays enriched in exchangeable aluminum that heavily influenced the soil chemical reactions over the expected importance of organic matter found in most studies conducted over Oxisol and Ultisol.     

饱和-非饱和介质水-应力耦合弹塑性二维有限元分析

从建立应力平衡方程、水连续性方程和弹塑性矩阵入手，使用Galerkin方法，将各控制方程分别在空间域和时间域进行离散，初步开发出了一个用于分析饱和-非饱和孔隙介质中水-应力耦合弹塑性问题的二维有限元程序。通过引入一组特定的与非饱和状态有关的计算公式，对一个假定的非饱和土体中水-应力耦合问题进行了数值计算，考察了不同时间土体中的位移、孔隙水压力、有效主应力、流速和塑性区的分布，定性验证了该程序的正确性。     

Collapse Loads for a Cylinder Embedded in Trench in Cohesive Soil

This study investigates the relationship between the sediment resisting force and embedment depth for horizontal cylinders in a vertical trench. Plane-strain calculations of collapse loads are performed for a series of trench depths. Collapse load predictions are based on finite element predictions validated by upper and lower bound solutions from classical plasticity theory. This study extends work by previous investigators by considering variable soil shear strength profiles and embedment depths exceeding one cylinder radius. Curve fits are applied to the finite element predictions to develop simplified equations relating collapse load to trench depth. The predictions are relevant to a number of applications, including pipeline penetration, waste disposal, and mine detection.     

Lateral Loaded Pile Response in Liquefiable Soil

This paper provides a new analysis procedure for assessing the lateral response of an isolated pile in saturated sands as liquefaction develops in response to dynamic loading such as that generated during earthquake shaking. This new procedure predicts the degradation in pile response and soil resistance due to the free-field excess porewater pressure generated by the earthquake, along with the near-field excess porewater pressure generated by lateral loading from the superstructure. The new procedure involves the integration of the developing (free- and near-field) porewater pressure in the strain wedge (SW) model analysis. The current SW model, developed to evaluate drained response (a nonlinear three-dimensional model) of a flexible pile in soil, has been extended in this paper to incorporate the undrained response of a laterally loaded pile in liquefied sand. This new procedure has the capability of predicting the response of a laterally loaded isolated pile and the associated modulus of subgrade reaction (i.e., the p–y curve) in a mobilized fashion as a result of developing liquefaction in the sand. Current design procedures assume slight or no resistance for the lateral movement of the pile in the liquefied soil which is a conservative practice. Alternatively, if liquefaction is assessed not to occur, some practitioners take no account of the increased free-field porewater pressure, and none consider the additional near-field porewater pressure due to inertial interaction loading from the superstructure; a practice that is unsafe in loose sands.     

土壤矿物钾的释放及其在植物营养中的意义

本文对土壤钾的形态、矿物钾释放的影响因素及钾的固定、土壤含钾矿物与土壤供钾能力间关系、矿物钾的植物有效性进行了综述 ,表明土壤钾素从有效性的角度进行划分时 ,不能仅把速效性钾和1mol/L热硝酸提取的缓效性钾列为作物吸钾的主要来源 ,而忽视矿物钾的作用 .