Influence of Soil Air Permeability Change on Soil Vapour Extraction Systems Design

Soil air permeability plays a decisive role in the effectiveness of soil vapour extraction (SVE) for the removal of volatile organic contaminants (VOCs) from soil. The objective of this work is to study the change of the soil air permeability during continuous venting and removal of contaminant from a polluted soil. SVE pilot experiments were conducted to investigate the interaction of soil air permeability with total liquids saturation. Oppositely to previous studies, air permeability was measured by fitting pressure data measured in a 3D laboratory venting pilot to an analytical airflow solution. The experimental correlation was compared with two different correlations published previously. A difference was observed between measured and calculated air relative air permeabilities especially for low water saturation degrees. The importance of the correct estimate of relative permeability was then illustrated by comparing vacuums and streamlines calculated using measured permeability and permeability values estimated with the two correlations tested here. Results show that an inappropriate assessment of relative permeability may engender significant errors in designing an SVE system. The second part of this work reports on the influence of air permeability change on the prediction capability of an SVE mathematical model. A significant difference between simulated breakthrough curves, estimated using firstly the relationship established experimentally and secondly the two other correlations, was observed. These results lead us to say that inadequate characterization of the air permeability change may generate significant errors in removal rate and closure time estimates.     

Using a Simple Soil Column Method to Evaluate Soil Phosphorus Leaching Risk

The impacts of soil P leaching on water eutrophication have widely been concerned. However, there is no dependable method to quantitatively estimate the P leaching risk of soils. In this study, a simple soil column method was developed using two calcareous Fluvisols, silt loam and loam. The soil column was 20 cm in length and 5 cm in diameter, and distilled water was continuously supplied from the top. The volume and dissolved reactive P (DRP) concentrations of leachate were measured. Results showed that DRP concentrations in leachate increased slowly for the low soil Olsen‐P levels but rapidly for the high Olsen‐P levels. According to these two‐phase changes in the DRP versus soil Olsen‐P contents, the thresholds of P leaching risk were estimated to be 41.1 and 62.3 mg P kg^?1 (Olsen‐P) for silt loam and loam, respectively. The P leaching intensity of soils increased by 3‐ to 540‐fold if the soil Olsen‐P contents accumulated from 6.6 to 155.5 mg P kg^?1. The outcomes derived from this study regarding the determination of P leaching threshold and intensity by the soil column method also need a further verification on more soils with a wide range of physical and chemical properties.     

A Modified Soil Moisture Model for Two‐Layer Soil

There can be marked variations in soil hydraulic properties in a soil vertical profile from the soil surface to the base of the root zone. Many existing two‐layer soil moisture (TLSM) models cannot well describe typical stratified soil profiles. A modified TLSM model is presented in this study. The modified model results and those from two existing models are compared with field observations. The modified TLSM model had the best agreement with the field observations. In both the surface layer and the root zone layer, the root mean square errors of soil moisture estimated by the modified model were smaller than those for the other models. The parameters in the modified TLSM model are relatively easy to determine. The modified TLSM model offers clear advantages over current TLSM models.     

昆明盆地土体动力参数对土层地震反应影响研究

土动力参数是土层地震反应分析的重要参数之一,且具有较强的区域性特点。本文统计分析昆明盆地区域内101个场地的94组粉土和167组黏土的动三轴试验数据,并通过土层地震反应分析计算,与袁晓铭的推荐值和《工程场地地震安全性评价工作规范》(DB001-94)中给出的规范值做对比。结果表明:三种不同的土动力参数存在较大差异,对土层地震反应分析结果亦有较大的影响,随着超越概率的降低,对峰值加速度、反应谱和特征周期的影响更加明显;统计的土动力参数与实际值对应的土层地震反应分析结果较接近,因此统计的粉土和黏土土动力参数在昆明盆地具有一定的代表性和适用性,在Ⅱ、Ⅲ级工程场地地震安全性评价工作中具有一定的借鉴和参考作用。     

Soil Gas Sampling for 1,4‐Dioxane during Heated Soil Vapor Extraction

Soil gas sampling for 1,4‐dioxane at elevated soil temperatures, such as those experienced during in‐situ thermal treatment, has the potential to yield low results due to condensation of water vapor in the ambient temperature sampling vessel and the partitioning of 1,4‐dioxane into that condensate. A simple vapor/condensate sampling apparatus was developed to collect both condensate and vapor samples to allow for determination of a reconstituted effective soil gas concentration for 1,4‐dioxane. Results using the vapor/condensate sampling apparatus during a heated air injection SVE field demonstration are presented, along with those of a comparable laboratory system. Substantial 1,4‐dioxane mass was found in the condensate in both the lab and field (as high as ~50% in field). As soil temperatures increased, less 1,4‐dioxane mass was detected in field condensate samples than expected based on laboratory experiments. Extraction well effluent sampling at the wellhead by direct vapor canister sampling provided erratic results (several biased low by a factor of 5 or more) compared to those of the vapor/condensate apparatus. Direct vapor canister sampling of extraction well effluent after the air‐water separator, however, provided results reasonably comparable (within 35%) to those using the vapor/condensate apparatus at the wellhead. Soil gas sampling at elevated temperatures using the vapor/condensate apparatus alleviates potential low sampling bias due to condensation.     

Soil acidity adaptive control problem

Problem of soil acidity regularization is modeled as stochastic adaptive control problem with a linear difference equation of the dynamics of a field pH level. Stochastic component in the equation represents an individual time variability of soil acidity of an elementary section. We use Bayesian approach to determine a posteriori probability density function of the unknown parameters of the stochastic transition process. The Kullback–Leibler information divergence is used as a measure of difference between true distribution and its estimation. Algorithm for the construction of an adaptive stabilizing control in such a linear control system is proposed in the paper. Numerical realization of the algorithm is represented for a problem of a field soil acidity control.     

北海市土层剪切波速与埋深的关系

收集了2008年以来北海市城区44个工程场地地震安全性评价中的土层剪切波速测试资料,采用幂函数模型分别对粘土、粗砂、砾砂、其它土类的土层剪切波速与埋深进行加权回归分析,得到不同土类的模型参数及拟合优度指标(判定系数R2和误差标准差σ),并对回归方程和回归系数进行了显著性检验;最后将土层剪切波速预测值与实测值进行对比,验证回归关系式的合理性和适用性。结果表明:北海市城区土层剪切波速与埋深呈现出较好的幂函数关系,拟合优度均在0.81以上;给出的土层剪切波速回归关系式能较好地预测出不同埋深土层剪切波速,特别是在土层中部和底部推测结果准确性更高,其推测结果可供北海市城区缺乏剪切波速测试资料的场地参考使用。     

杭州市典型土层剪切波速与埋深间的关系分析

基于杭州市丰富的场地钻孔剪切波速资料,采用3种常见的剪切波速与埋深回归分析模型,分析杭州地区5类常规土在场地分类和场地未分类情况下的最优拟合公式和预测范围,并对推荐模型进行可靠性验证,对常规粉质粘土和粉砂进行地区差异性分析。研究结果表明:本文推荐的剪切波速与埋深关系公式具有良好的可靠性;地区、岩土类型和预测深度均对剪切波速与埋深关系模型的可靠性产生显著影响,故应用时应优先选用本地区统计模型,如若未有,则需根据已有资料,对选用模型进行岩土类型和适应预测深度范围验证,以保证所选模型的可靠性;受地区、岩土类型和预测深度的影响,考虑场地分类并不一定提高统计模型的预测精度,在实际工程应用中具有不确定性。     

干旱地区单层及多层介质土壤中降低接地电阻的方法

以甘肃省酒泉市金塔地区某变电站工程为实例,对戈壁、沙漠等高土壤电阻率地区如何降低接地电阻进行了组合分析。由于干旱地区年降雨量低,日照时间长,蒸发量大,用常规的降阻剂或局部更换土壤等方法难以长期稳定的解决高土壤电阻率地区接地电阻过大的问题。本文采用了一些特殊方法进行处理,这对促进此类地区电力建设项目及其他项目建设具有重要意义。     

地基液化导致沉箱码头破坏及地基加固方法的非线性数值分析

地震作用引发的地基液化,往往导致沉箱基础的破坏。本文基于Biot两相饱和多孔介质动力耦合理论,采用FE-FD耦合数值分析方法,对液化海床沉箱基础的地震反应进行非线性有效应力分析。在数值分析过程中,建立了以土骨架位移和超静孔隙水压力表达的us-pw动力固结方程和循环弹塑性本构模型,该方法能够很好地模拟地震作用下沉箱码头的动力特性及液化破坏的影响。通过数值模拟计算,分析了采用碎石桩进行置换砂区域的防液化加固方法,并就碎石桩处理区域的选择提出了建议。     

Soil deformation and its spectral signature

Spatial variation of the surface micro‐relief in a Sharkey clay soil was investigated. The micro‐relief measurements of the soil surface were obtained using an automated infrared laser system and evaluated with methods of Fourier analysis. The authors illustrate the spectral technique with a simple example and then use the technique to interpret the surface micro‐relief patterns of soil samples subjected to three simulated rainstorm intensities. The periodicity of the soil surface micro‐relief in the longitudinal direction was 80–120 mm. The periodic surface micro‐relief patterns immediately following the rainstorm are shown to be an early manifestation of the cracking pattern. Published in 2006 by John Wiley & Sons, Ltd.     

Effects of Rhizosphere Ventilation on Soil Enzyme Activities of Potted Tomato under Different Soil Water Stress

In order to improve the growing environment of root zone, and investigate the effects of different rhizosphere ventilation environments on soil enzyme activities, we supplied gas for potted tomato by air compressor, and set three irrigation levels (70–90% field capacity). Each irrigation level has different ventilation volume coefficient (0.4, 0.8, 1.2, and 1.6) with the reference standard as 50% soil porosity. The results showed that the changing trend of soil catalase, urease, and dehydrogenase activity showed the first increase and then the decrease in the tomato growth period, and activities of soil catalase, urease, and dehydrogenase under the ventilation treatment are higher than those of the non‐ventilation. When the irrigation level was 80% the field capacity and the ventilation coefficient was 0.8, the activities of three soil enzyme reached the highest value. Their activities of soil catalase, urease, and dehydrogenase were particularly sensitive to rhizosphere ventilation in fruit expanding process. Tomato had more dry matter accumulation and output under the ventilation treatment than that of the non‐ventilation. The results prove that rhizosphere ventilation can improve the potted tomato root zone environment, increase the soil enzyme activity, and promote the nutrients uptake, thus promoting plant growth and fruit output and improving soil quality.     

Soil amplification of plane seismic waves

Amplitudes of surface particle velocities are calculated when time-harmonic seismic waves of uniform amplitude are incident upon an arbitrary stratified elastic soil layer from the underlying bedrock. Whereas previous workers have mainly treated normally incident S waves, we allow the waves to be of SV, P, or SH types and to have arbitrary angles of incidence. Following standard practice the problem is set up as a matrix differential system, but in such a way that incident SV and P waves may be treated together (the system for SH decoupling). Though complicated, the 4 × 4 SVP system has considerable structure which is elucidated in Appendices 1 and 2. These results, though not altogether new, are of independent interest, and are gathered together in concise form for reference. The theory for low- and for high-frequency approximations is given. The main results of the work are illustrated by two numerical examples: Model 1 where the soil layer is homogeneous; and Model 2 where the soil layer has a linear velocity profile.