Hydraulic conductivity of shallow sandy aquifers: Effects of sedimentologic and diagenetic differences

The relationship between values of hydraulic conductivity determined from grain-size methods,K _gr, and those from pumping-test methods,K _pt, have been evaluated statistically using data from recent and older sandy materials. It is shown that both methods generally give the same values only in recent sediments that have not been subjected to significant diagenetic alteration and give variable results in older and diagenetically altered sediments. The ratioK _pt/K_gr appears to vary, probably in response to the degree of diagenetic alteration. It is further found that methods incorporating the effects of grain size (d1O or d50) and sorting could give betterK values than those incorporating the effect of grain-size only and, thus, suggest the joint inclusion of both parameters in the grain-size determination of permeability.     

Environmental geological and geotechnical investigations related to the potential use of Ankara clay as a compacted landfill liner material, Turkey

Clay-bearing Upper Pliocene red clastics and Quaternary alluvial deposits occupy the Ankara basin. The clayey levels of the Upper Pliocene deposits, referred to as Ankara clay, is considered as a source for compacted clay liners due to their low coefficients of permeability and widespread distributions throughout Ankara. This study investigates the geological, geotechnical and mineralogical properties of the founding clayey soils at two sites of the Ankara region. The geotechnical index properties along with the hydraulic conductivities of the clayey soil samples collected from these sites were determined. A mathematical relation between the clay mineralogical content and hydraulic conductivity was established. The results of this investigation show that, from a geotechnical point of view, Ankara clay may be regarded as a highly suitable material for a compacted clay landfill liner given that its mineralogical compatibility with leachate is confirmed.     

Weathering of Valle Ricca stiff and jointed clay

The study proposes a weathering model of Pliocene–Pleistocene stiff and jointed blue-grey clay transforming into yellow clay. Physical, mineralogical, chemical and textural changes, as well as the weathering profile were investigated in a quarry of central Italy. Based on geological records and inferences, these changes are likely to have occurred within a time-span of about 50,000 years BP, upon overburden stress unloading and in a stress regime that is locally controlled by suction. Weathering propagated into the clay at a rate of about 0.3 mm/year and was enhanced by the enlargement of the pre-existing tectonic discontinuities and by the formation of new joints. A mass loss of about 22–25 wt.% was calculated. Considering Fe and P as immobile elements, the individual oxides contribute to mass loss in the following order: SiO₂ > CaO = CO₂ > Al₂O₃ > MgO > K₂O > S > Na₂O > TiO₂ > MnO. The Fe₂O₃ / (Fe₂O₃ + FeO) ratio varies from 9–29% in the blue-grey clay to 75–82% in the yellow one. Oxidation and/or dissolution of 7 Å-Fe²⁺-bearing clay minerals, mica-like minerals and calcite and parallel increase of smectite and Fe-hydroxides play a critical role in the chemical changes and explain the higher plasticity of the yellow clay with respect to the blue-grey one. The role of water during the weathering process was inferred to occur in cyclical steps: 1) seepage of meteoric water; 2) dissemination of highly oxidizing meteoric water; 3) triggering of oxidation and dissolution of minerals; 4) water evaporation; 5) partial migration of the elements contained in the aqueous solution and consequent deposition of minerals in the joints.     

Utilization of red mud as a stabilization material for the preparation of clay liners

Red mud is a waste material generated by the Bayer Process widely used to produce alumina from bauxite throughout the world. Approximately, 35% to 40% per ton of bauxite treated using the Bayer Process ends up as red mud waste. Because of storing issues, the waste negatively affects the environment. To solve this problem, it is essential to investigate different uses for red mud waste. The potential use of red mud for the preparation of stabilization material is presented in this study. This study examines the effects of red mud on the unconfined compressive strength, hydraulic conductivity, and swelling percentage of compacted clay liners as a hydraulic barrier. The test results show that compacted clay samples containing red mud and cement–red mud additives have a high compressive strength and decreased the hydraulic conductivity and swelling percentage as compared to natural clay samples. Consequently, it is concluded that red mud and cement–red mud materials can be successfully used for the stabilization of clay liners in geotechnical applications.     

Microstructure and hydraulic conductivity of a compacted lime-treated soil

Under a given compaction energy and procedure, it is known that maximum dry density of a soil is lowered due to lime addition. This modification of maximum dry density could alter the hydraulic conductivity of the soil. The main object of this study was to assess the impact of lime-stabilization on a silt soil microstructure and then on saturated hydraulic conductivity. An investigation at the microscopic level with mercury intrusion porosimetry showed that lime treatment induced the formation of a new small class, with a diameter lower than 3 × 10³ Å in the compacted soil. This class is responsible for the difference in dry density between the treated and the untreated sample after compaction. It is shown that this small pores class was not altered by the compaction water content, the compaction procedure or the dry density. As in untreated soils, only the larger pores were modified by the compaction water content and the compaction procedure in the lime treated samples. The hydraulic conductivity appeared to be only related to the largest pores volume of the tested silt, regardless of lime treatment. Therefore, this study demonstrated that even if addition of lime resulted in a dramatic change of the maximum dry density of the tested silty soil, its effect on hydraulic conductivity is limited.     

粘土衬垫中渗透系数与扩散系数的关系

扩散系数和渗透系数是设计与评价垃圾填埋场衬垫等环境工程研究时需要确定的重要参数。通过分析粘土衬垫材料中渗透系数和扩散系数的物理意义和确定方法,在土多孔介质微观结构分析的基础上得到渗透系数和扩散系数的关系表达式,并基于蒙脱石层间Poiseuille定律得到膨润土有效扩散系数的计算公式。验证表明,在一定精度范围内文中表达式是有效的。得出的渗透系数和扩散系数的关系表达式,对于根据已有渗透系数的研究成果来预测和分析扩散系数是有意义的。     

Measurement of streambed hydraulic conductivity and its anisotropy

 A method is described for the measurement of streambed hydraulic conductivity. Unlike permeameter methods, this method applies straight and l-shaped standpipes directly to streambeds for measurements of in-situ hydraulic conductivity in the vertical (K _v ) and horizontal (K _h ) directions, as well as in other oblique directions (K _s ). This method has advantages in determination of K _v values over grain-size analysis, permeameter tests, or slug test methods. Also unique to this method is that it provides K _s values of a streambed. The measured results can be used to construct a hydraulic conductivity ellipse and to evaluate the anisotropy of streambed sediments. Field examples from the Republican River, Nebraska, demonstrated the usefulness of this method in the determination of streambed hydraulic conductivity and anisotropy along or across a river channel. Results indicate that the K _h is about three to four times larger than K _v , whereas K _s values are larger than K _v but smaller than K _h . Received: 6 March 2000 · Accepted: 18 April 2000     

Hydraulic and compaction characteristics of leachate-contaminated lateritic soil

Large quantities of leachate-contaminated lateritic soil results from dump yards in the southwest coast of India. These dump yards receive large quantities of municipal solid waste which includes chemical, industrial and biomedical wastes. Large areas of land are currently being used for this purpose. An extensive laboratory testing program was carried out to determine the compaction characteristics and hydraulic conductivity of clean and contaminated lateritic soil. Batch tests were used to study the immediate effect of leachate contamination on the properties of lateritic soil. Contaminated specimens were prepared by mixing the lateritic soil with leachate in the amount of 5%, 10% and 20% by weight to vary the degree of contamination. The results indicated a small reduction in maximum dry density and an increase in hydraulic conductivity due to leachate-contamination. The change induced by chemical reaction in the microstructure of the soil was studied by scanning electron microscope before and after contamination of soil with leachate. The structure of the leachate contaminated soil sample appeared to be aggregated in scanning electron microscope analysis. The aggregated structure increases the effective pore space and thus increases the hydraulic conductivity. Fifty percent increase in hydraulic conductivity was observed for specimens prepared at standard Proctor density and mixed with 20% leachate. Compaction characteristics did not change much with the presence of leachate up to 10%. With 20% leachate the maximum dry density decreased slightly indicating excess leachate in the soil. However the changes are not significant.     

Hydraulic,textural and geochemical characteristics of the Ajali Formation,Anambra Basin,Nigeria: implication for groundwater quality

This study highlights the distribution of hydraulic conductivity (K) in the regional aquiferous Ajali Formation of SE-Nigeria on one hand and assesses the possible influences of textural and geochemical characteristics on the hydraulic conductivity on the other hand. The investigation approach involved field sampling and collection of 12 sandstone samples from different outcrop locations, followed by laboratory studies such as grain-size analysis (GSA), constant head permeameter test and geochemical analysis of major and trace elements using X-ray fluorescence method. GSA and textural studies show that the sandstones range from fine to medium sands, constituting about <75–99% sand fraction, with graphic mean grain size of 0.23–0.53 mm. Other parameters such as coefficient of uniformity (C_u) range from 1.58 to 5.25 (av. 2.75), while standard deviation (sorting) values of 0.56Ø–1.24Ø imply moderately well sorted materials. In addition, the order of the estimated K values is K_permeameter>K_Beyer>K_Hazen>K_{Kozeny-Carmen}>K_Fair-Hatch with average values of 1.4×10^?3, 4.4×10^?4, 3.8×10^?4, 2.2×10^?4 and 8.1×10^?5m/s, respectively. These values fall within the range of 10^?5 and 10^?3m/s for fine to medium sands. However, multivariate factor analysis of the data revealed significant positive dependence of the empirically determined K values on graphic mean grain size and percentage sand content and much less dependence on sorting and total porosity. Geochemical profiles of the fresh samples are dominated by quartz with corresponding SiO₂ content of 76.1–98.2% (av. 89.7%) while other major oxides are generally below 1.0wt.% in the fresh samples. However, the ferruginized samples exhibited elevated concentrations of Al₂O₃ (3.50–11.60wt.%) and Fe₂O₃ (1.80–3.60wt.%), which are clear indications of weathering/ferruginization processes with attendant trace metal release/enrichment (2.5mg/l Cu, 7.5mg/l Pb, 6.5mg/l Zn, 3.9mg/l Ni and 19.6mg/l Cr) call for concern in respect of the chemical quality of the groundwater system. The associated groundwater is generally soft, slightly acidic, and with low dissolved solids (EC=14–134μs/cm) dominated by silica; implying water from clean sandy aquifer devoid of labile and weatherable minerals. Nonetheless, most of the metals (with exception of Si, Fe and Mn) exhibited higher degree of mobility (2–12 folds), which can be attributed to reduction of Fe-/Mn-oxyhydroxides as sinks/hosts for trace metals. Consequently, infiltration-induced geochemical reactions (redox, ferruginization and leaching processes) signify potential environmental impact in terms of groundwater quality as well as borehole/aquifer management, especially under humid tropical environment of the study area.     

The hydraulic conductivity field and groundwater flow in the unconfined aquifer system of the Keta Strip,Ghana

This study investigates the hydraulic conductivity field and the groundwater flow pattern as predicted by a calibrated steady state groundwater flow model for the Keta Strip, southeastern Ghana. The hydraulic conductivity field is an important parameter in evaluating aquifer properties in space, and in general basin-wide groundwater resources evaluation and management. This study finds that the general hydraulic conductivity of the unconsolidated unconfined aquifer system of the Keta Strip ranges between 2 m/d and 20 m/d, with an average of 15 m/d. The spatial variation in horizontal hydraulic conductivity appears to take the trend in the variations in the nature of the material in space. Calibrated groundwater recharge suggests that 6.9–34% of annual precipitation recharges the shallow aquifer system. This amount of recharge is significant and suggests high fortunes in terms of groundwater resources development for agriculture and industrial activities in the area. A spatial distribution of groundwater recharge from precipitation is presented in this study. The spatial pattern appears to take the form of the distribution in horizontal hydraulic conductivity, and suggests that the vertical hydraulic conductivity takes the same pattern of spatial variation as the horizontal hydraulic conductivity. This is consistent with observations in other areas. The resulting groundwater flow is dominated by local flow systems as the unconfined system is quite shallow. A general northeast – southwest flow pattern has been observed in the study area.     

A coupled analysis of cavity and pore volume changes for pulse tests conducted in soft clay deposits

This paper presents a new interpretation method for pulse tests, a field permeability test that allows for rapid measurements of hydraulic conductivity k in aquitards. This new method applies to soft clay deposits. To initiate a pulse test, a known volume of water is injected into the sand filter of a monitoring well isolated by a packer. The resulting pressure increase yields an outward movement of the sand filter cavity wall. After presenting the usual interpretation methods and their limits, this paper proposes a new interpretation method based on a coupled analysis of the pressure and displacement fields in the soil using the Biot–Darcy formulation. A series of analytical and numerical non‐dimensional velocity graphs, normalized plots of the mean hydraulic head difference versus its rate of change, are given. For a linear elastic material, these type curves show relatively small variations with the sand filter aspect ratio and the Poisson ratio of the tested clay. The type curves are also found to be independent of the clay compressibility (m_v) and k, an important result. A series of pulse tests conducted in a soft marine clay deposit near Montreal, Canada, are interpreted with the proposed method. The hydraulic conductivity values calculated from these tests are closely correlated with independent estimates obtained using long‐duration variable‐head tests. Compared with previous interpretation methods, the proposed method allows soil volume changes to be reconciled with cavity expansion phenomena and the range of type curves available for the interpretation of test data to be constrained. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of salt of various concentrations on liquid limit,and hydraulic conductivity of different soil-bentonite mixtures

Effect of the various concentrations of NaCl and CaCl₂ on the four different soil-bentonite mixtures has been evaluated. The results show that the liquid limit of the mixtures decreases with an increase in the salt concentration. Liquid limit decreased significantly with an increase in CaCl₂ concentration from 0 to 0.1 N. However, a further increase in the concentration did not produce any significant decrease in liquid limit. A quite opposite trend was observed for the NaCl solution. An increase in NaCl concentration from 0 to 0.1 N did not produce any major decrease in the liquid limit, but a further increase in concentration from 0.1 to 1 N decreased the liquid limit significantly. Consolidation tests were carried out on the mixtures to evaluate the effect of mineralogical composition of the bentonite on the hydraulic conductivity (k) of the mixture in the presence of various salts concentrations. The k for any mixtures was found to be decreasing with decrease in the salt concentration. At relatively low concentration, Ca²⁺ had more effect on the k in comparison to the same concentration of Na⁺. However, at 1 N of NaCl and CaCl₂ almost an equal value of k was observed. A comparison of the performance of four bentonites showed that the mixture with bentonite having highest exchangeable sodium percentage (ESP) exhibited the lowest k when permeated with de-ionized (DI) water, however, k increased with an increase in the salt concentration. Similarly, mixture with a bentonite of lower ESP exhibited a higher k with DI water but with the increase in the salt concentration alteration in the k, compared to all other mixtures, was relatively less.     

Estimating hydraulic conductivity using grain-size analyses, aquifer tests, and numerical modeling in a riverside alluvial system in South Korea

Hydraulic conductivity (K) for an alluvial system in a riverbank filtration area in Changwon City, South Korea, has been studied using grain-size distribution, pumping and slug tests, and numerical modeling. The alluvial system is composed of layers: upper fine sand, medium sand, lower fine sand, and a highly conductive sand/gravel layer at the base. The geometric mean of K for the sand/gravel layer (9.89?×?10^?4 m s^?1), as determined by grain-size analyses, was 3.33 times greater than the geometric mean obtained from pumping tests (2.97?×?10^?4 m s^?1). The geometric mean of K estimates obtained from slug tests (3.08?×?10^?6 m s^?1) was one to two orders of magnitude lower than that from pumping tests and grain-size analyses. K estimates derived from a numerical model were compared to those derived from the grain-size methods, slug tests and pumping tests in order to determine the degree of deviation from the numerical model. It is considered that the K estimates determined by the slug tests resemble the uppermost part of the alluvial deposit, whereas the K estimates obtained by grain-size analyses and pumping tests are similar to those from the numerical model for the sand/gravel layer of the riverside alluvial system.     

Relationships between hydraulic conductivity distribution and synsedimentary faults,Rharb-Mamora basin,Morocco; Hydrogeological,geostatistical and modeling approaches

This paper deals with the relationship between the physical characteristics of the Rharb-Mamora basin (Northern Morocco) and the distribution of hydraulic conductivity values in the Plio-Quaternary aquifer. A steady state groundwater model has been calibrated using these values. The distribution of hydraulic conductivity corresponds to a hydrodynamic partition with permeabilities of 2×10^–3 to 5×10^–2 ms^–1 (in the coastal part). A numerical modeling process shows a relative error map between calculated and measured piezometric surfaces, in order to facilitate calibration in steady state.The distribution of hydraulic conductivity values, and the lateral variation of sequences (deduced from engineering geology methods e.g. hydrogeological drilling data, seismic reflection interpretation, and geostatistical analysis), are controlled by synsedimentary fault activity, which deepened the Mio-Pliocene basement resulting in a thickening of overlying permeable rocks.

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Resumen Esta nota trata la relación existente entre las características físicas y la distribución de la conductividad hidráulica de los acuíferos subyacentes de la cuenca del Rharb-Mamora (norte de Marruecos). Para la simulación del flujo del agua subterránea se ha establecido un modelo en régimen permanente. La distribución de la conductividad hidráulica corresponde a un reparto hidrodinámico cuyo grado de permeabilidad es generalmente alto: desde 2×10^–3 hasta 5×10^–2 ms^–1 (zona costera). Con el objetivo de facilitar la calibración del modelo en régimen permanente, el proceso numérico realizado mostró errores relativos entre la piezometría calculada y medida. La distribución de los valores de permeabilidad y la variación lateral de las unidades permeables ha sido deducida a partir de métodos de geología aplicada (análisis de los sondeos hidrogeológicos, interpretación de los perfiles de sísmica de reflexión y aplicación de métodos geoestadísticos), y están controlados por la actividad de las fallas sinsedimentarias que influyen sobre la topografía del basamento mio-plioceno y el grosor de las unidades acuíferas.

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Résumé Cette note traite la relation entre les caractéristiques physique du bassin Rharb-Mamora (Nord du Maroc) et la répartition de la conductivité hydraulique du réseau aquifère. Le modèle de simulation des écoulements souterrains a été établi en régime permanent. La distribution de la conductivité hydraulique correspond à un découpage hydrodynamique dont le degré de perméabilité est généralement bon entre 2×10^–3 to 5×10^–2 ms^–1 (zone côtière). Afin de faciliter le calage en régime permanent, le code numérique établi permet de mettre en évidence les erreurs relatives entre la piézométrie calculée et mesurée.La distribution des valeurs de perméabilité et la variation latérale des unités perméables, déduites des méthodes de la géologie appliquée (analyse des forages hydrogéologiques, interprétation des profils sismique réflexion et analyse géostatistique), sont contrôlées par lactivité des failles synsédimentaires qui influencent lapprofondissement du substratum hydrogéologique mio-pliocène et lépaississement des corps perméables.

     

Evolution of pore structure and hydraulic conductivity of randomly distributed soluble particle mixture

The plane strain behavior of particulate mixtures containing soluble particles was investigated by conducting both laboratory tests and numerical analysis. To perform the laboratory experiments, soluble mixtures were prepared using photoelastic disks and ice disks with diameters in the ratios (D_{ice disk}/D_{photoelastic disk}) of 0.5 and 0.7, and the evolution of the force chain and pore structure was monitored during the dissolution of the ice disks. Subsequently, numerical analysis was conducted by using the 2‐dimensional discrete element method for the soluble mixtures, and it was compared with the experimental results. Additionally, parametric studies were implemented by varying the particle size ratios between the soluble and non‐soluble particles and the volumetric fraction of the soluble particles. The results of the laboratory experiments and numerical analysis demonstrate that (1) after the dissolution of the soluble particles, the pore fabric of the specimens changed, resulting in a force chain changes, local void increases, and coordination number decreases; (2) the effects of soluble particles on the macro‐behaviors of the mixtures could be divided into 3 zones based on the particle size ratios between the soluble and non‐soluble particles and volumetric fraction of soluble particles. These zones were as follows: (Zone 1)—with a small total soluble volume, slight decrease in the in situ lateral pressure (K₀), and minor increase in the hydraulic conductivity (k); (Zone 2)—with a moderate soluble particle; the dissolution generated a honey‐comb particle structure; (Zone 3)—the total soluble volume was very large, and the high volumetric fraction of the dissolving particle collapsed the pore structure, decreasing in the in situ lateral pressure (K₀) but increasing the hydraulic conductivity (k). The horizontal stress returned to almost the original level, and the internal arching formation increased significantly with the hydraulic conductivity (k).     

An empirical model for estimating hydraulic conductivity of highly disturbed clastic sedimentary rocks in Taiwan

This paper presents the establishment of an empirical HC model for estimating rock mass hydraulic conductivity of highly disturbed clastic sedimentary rocks in Taiwan using high-resolution borehole acoustic televiewer and double packer hydraulic tests. Four geological parameters including rock quality designation (RQD), depth index (DI), gouge content designation (GCD), and lithology permeability index (LPI) were adopted for establishing the empirical HC model. To verify rationality of the proposed HC model, 22 in-situ hydraulic tests were carried out to measure the hydraulic conductivity of the highly disturbed clastic sedimentary rocks in three boreholes at two different locations in Taiwan. Besides, the model verification using another borehole data with four additional in-situ hydraulic tests from similar clastic sedimentary rocks was also conducted to further verify the feasibility of the proposed empirical HC model. The field results indicated that the rock mass in the study area has a conductivity between the order of 10^− 10 m/s and 10^− 6 m/s at the depth between 34 m and 275 m below ground surface. Results demonstrate that the empirical HC model may provide a useful tool to predict hydraulic conductivity of the highly disturbed clastic sedimentary rocks in Taiwan based on measured HC-values.     

Fluid permeability of sedimentary rocks in a complete stress–strain process

The permeability of sedimentary rocks during triaxial compression tests was investigated to relate it to the complete strain–stress process. It was found that the permeability was not constant, but varied with the stress and strain states in the rocks. Prior to the peak strength, the permeability decreases with increasing load. A dramatic increase in permeability occurs during the strain softening period. In the present study, in situ measurements of fluid flow and pressure in floor strata was carried out in a double longwall mining face in the Yangzhuang colliery. These measurements show that both the strata pressure and the position with respect to the mining face influence the hydrogeologic properties. The permeability increased in the floor strata behind the mining face because those mining induced fractures opened as the strata pressure decreased. To better understand this change in hydraulic behavior around the mining faces, 3-D numerical modeling was carried out. The model provides the general picture of the stress distribution and failure zone both in the floor and roof strata. The field and model results demonstrate the importance of changes in the stress and strain states on the hydrogeology of a site.     

Mechanics and fluid transport in a degradable discontinuity

This paper briefly examines the mechanical and hydraulic response of discontinuity in a geologic medium that can experience degradation of its contacting regions due to shear and normal stresses acting on it. The paper discusses the methodologies that can be adopted to describe the mechanics and fluid transport behaviour of such a joint. The calibration capabilities of the model are illustrated by appeal to a comparison of experimental results with computational predictions.     

北京平原区粉质粘土热导率影响因素实验研究

岩土体热导率是热物理性质重要参数之一,不仅仅决定着浅层地温场的展布形态,而且也是整个热泵功率计算的核心,是影响地源热泵工程投资和运行能耗的关键因素.本文通过一系列实验,对粉质粘土的热导率与含水量、密度、孔隙比进行研究和统计,从实验研究结果来看,粉质粘土热导率随着含水量的增大而增大,可以用对数关系和乘幂关系进行拟合,相关系数较好,由于样品物质成分和微观结构差异影响着传热方式组合,难以用统一的拟合方程表示同一地区热导率与含水量等因素变化规律.在含水率不变的情况下随着孔隙比的增大而热导率逐渐减小,随密度的增加而热导率增大的规律趋势明显.粉质粘土热导率随含水量的变化可分为3个阶段,含水量在0～5％,热导率随之增加急剧,含水量5％～20％时,热导率随之增加较快,含水量大于20％时,热导率随之增加缓慢并趋于稳定.