Nondestructive test to track pollutant transport into landfill liners

Over the last decade, waste disposal has become a particularly sensitive issue in Algeria. New legislation concerning landfill liner design has been adopted. Traditional methods of landfill liner characterization involve soil sampling and chemical analysis, which are costly, destructive and time-consuming. New techniques are currently being investigated that aim to provide nondestructive liner characterisation. This paper details technical aspects associated with electrical conductivity measurements within landfill liners and presents experimental work to show the direct application of electrical techniques to track ionic movement through a sand bentonite liner under chemically induced flow. Samples of sand bentonite were mixed and compacted with NaCl electrolytes at different concentrations. The electrical conductivities of compacted specimens were measured with a two-electrode cell. The effects of frequency and electrolyte concentration on the conductivity measurement were explored. The relationship between the soil electrical conductivity and the NaCl electrolyte concentration in interstitial pore fluid was determined. The conductivity measurements were used to quantify the pore fluid concentration and effective diffusion coefficient of sand bentonite liners. It is concluded here that the electrical conductivity of compacted specimens depends mainly on the salt concentration in the pore fluid, and that this approach could therefore be used to track ionic movement through liners during diffusion.     

层状介质二维电阻率扰动反演方法

为解决考古、工程地质和地下水污染勘查中某些探测靶体与周围介质间电性差异不大的地质问题,本文提出了层状介质背景下二维电阻率扰动反演方法．根据观测得到的背景剖面视电阻率断面,确定出背景场的电性层结构,利用电阻率扰动方法计算出敏感矩阵,通过广义逆矩阵法求解出电阻率的增量．在商丘地下夯土城墙的应用表明,该方法有效地抑制了夯土城墙的旁侧效应和地下水噪声的影响,揭示出地下夯土城墙的埋深与几何形态．     

Electrical-hydraulic conductivity model for a weatheredfractured aquifer system of Olbanita,Lower Baringo Basin,Kenya Rift

Groundwater yield in the Kenya Rift is highly unsustainable owing to geological variability.In this study,field hydraulic characterization was performed by using geoelectric approaches.The relations between electrical-hydraulic(eh)conductivities were modeled hypothetically and calibrated empirically.Correlations were based on the stochastic models and field-scale hydraulic parameters were contingent on pore-level parameters.By considering variation in pore-size distributions over eh conduction interval,the relations were scaled-up for use at aquifer-level.Material-level electrical conductivities were determined by using Vertical Electrical Survey and hydraulic conductivities by analyzing aquifer tests of eight boreholes in the Olbanita aquifer located in Kenya rift.VES datasets were inverted by using the computer code IP2Win.The main result is that ln T=0.537(ln Fa)+3.695;the positive gradient indicating eh conduction through pore-surface networks and a proxy of weathered and clayey materials.An inverse(1/F-K)correlation is observed.Hydraulic parameters determined using such approaches may possibly contribute significantly towards sustainable yield management and planning of groundwater resources.     

电阻率层析成像及演中若干问题的讨论

以双异性点电流源电流场二维地电断面为例，着重讨论了电阻率展析成像反演中有限单元法数值模拟边界条件的选择、网格剖分以及模拟精度等问题，同时也讨论了成像反演中最优化及演方法及拟合参数的评价等。文中提出的新的网格剖分方法和选择的边界条件可有效地提高计算速度和数值模拟的精度。     

Detection and hydrologic modeling of aquifers in unconsolidated alluvial plains through combination of borehole data sets: a case study of the Arao area, Southwest Japan

In addition to spatial distribution of groundwater-flow parameters, aquifer properties of location and shape are also significant for assessing groundwater resources because they strongly affect water flow. We present a selection of geologic data suitable for aquifer analysis, a mathematical method of processing them, and a combination of several maps produced by it. The data used in the analysis are typically obtained by borehole investigation. Our targets are the areas underlain by geologic bodies with different ages and lithologies; the spatial correlation structures of geologic data over the areas tend to change locally. The processing method should be a versatile one that is applicable to areas where geostatistical stationarity is not satisfied. The aquifer analysis consistent with that requirement consists of two steps: the first is the transformation of screen locations, locations of sand and gravel layers, and resistivity by electric logging into indicator values, and the second is three-dimensional interpolation of these using the optimization principle method to produce three kinds of distribution models. A stochastic simulation is also used for modeling the resistivity distribution. The three distribution models are integrated to generate a value for evaluating the possibility of aquifer existence. A case study of an alluvial coastal plain, situated in southwest Japan, describes an aquifer model that contains three permeable layers. Each layer has about 10-m thickness and is lens shaped. To confirm the validity of the model, we have drilled two wells that reached one of the middle and bottom permeable layers, observing the water level change. Low correlation of the temporal changes of levels between the wells indicates that the two layers are hydrologically independent of each other. Additionally, groundwater-flow patterns have been estimated by transforming the simulation model parameter into hydraulic conductivity through a simple function and using a finite difference method for flow analysis. The procedure proposed by this study can be applied to other areas by changing the weights assigned to each geologic and geotechnical factor in the generation of the coefficient for aquifer existence, considering the reliability of each factor and hydrologic properties of study area.     

Use of a resistivity cone for detecting contaminated soil layers

A cone-penetration technique was developed to detect contaminated soil layers with electrolytes and NAPLs. In this study, laboratory and field experiments were performed to apply the technique. In the laboratory, the change in resistivity was quantitatively examined by adding salt or oil to soil samples. The results showed that the resistivity measurement was varied with an order of ppm for the electrolyte concentration in soil. It was found that the resistivity of sand increased with increasing oil concentration. The effect of oil content was stronger for lower water content of sand.

The results obtained from field experiments showed that the resistivity cone can be used for detecting the contaminated layer in soils whose background values are known. Particularly, the instrument can be used effectively for examining the effects of remediation, by measuring the resistivity of the ground before and after remediation, unless the soil fabric changes significantly during remediation procedures.     

地电阻率变化与孕震过程研究

在分析唐山７．８级地震前后地电阻率异常变化特征的基础上，研究地电阻率异常量△ρ／ρ０与应变的关系，给出了地电阻率异常量△ρｓ／ρ０对应变ε的转换关系式；分析和研究地电阻率异常发展，演变特征与地震孕震，发生过程的联系及其前兆异常标志。     

电测深曲线的遗传算法反演

电测深曲线作为地下介质电阻率和深度的非线性函数，其解具有高度的非唯一性．常规的基于局部线性化的最优化反演方法易使解估计陷入局部极大值中，而且严重地依赖初始模型的选择．遗传算法作为一种全局最优化方法，对初始模型的依赖性大为减弱，且不易陷人局部极大值之中，从而能有效地解决这类非线性最优化问题．本文首次将遗传算法用于电测深解释并对实测曲线进行反演，效果很好，显示了遗传算法独特的优越性．     

视电阻率对模型电阻率的偏导数矩阵计算方法

按Tripp et al.(1984)提出的理论，给出了一种视电阻率对模型电阻率的偏导数矩阵简便计算方法，它的核心是互换定理。只要得到所有供电和测量电极节点分别供单位电流时各有限元网格节点上的电位，通过线性组合就可得到视电阻率对模型电阻率的偏导数。     

矿物电导率补偿效应研究及其对元素扩散性质的制约

根据已有的大量矿物电导率实验数据，我们观察到方解石、刚玉、顽火辉石、铁辉石、橄榄石、白榴石和方镁石电导率存在类似于元素扩散一样的补偿效应，即同一矿物在不同条件下测得电导率指前因子的对数lnσ0和活化能E之间有良好的线性关系，并利用橄榄石在不同时期、用不同样品得到的电导率数据进行了验证。文中还注意到同一矿物中不同导电机制或不同导电载流子产生的电导率也满足补偿效应，据此特点提出了应用矿物电导率补偿效应计算元素扩散系数中指前因子的新方法。