Magnitude Of Hydraulic Conductivity Research Articles

A Method for Estimating the Highest Potential Hydraulic Conductivity in the Excavation Damaged Zone in Mudstone

Excavation of deep underground openings induces permeable fractures around the opening due to stress redistribution. Such a zone is called excavation damaged zone (EDZ). In a high-level radioactive waste disposal project, the EDZ might provide pathways for the migration of radionuclides around the facility. Thus, this study focused on the development of a method for estimating the highest potential hydraulic conductivity in the EDZ around a gallery in the Horonobe Underground Research Laboratory, Japan. Borehole televiewer surveys, rock core observations, and hydraulic tests were undertaken to investigate the extent and magnitude of hydraulic conductivity in the EDZ around the gallery. The observed extent (sidewall ≤ 0.6 m; floor ≤ 1.6 m) of the EDZ shows good agreement with the EDZ estimated from hydro-mechanical coupling analysis. The measured hydraulic conductivities of the EDZ (3.5 × 10−6 to 1.24 × 10−8 m/s) are within the range of those based on the Mean Stress Index (MSI), which is defined as the ratio of the effective mean stress derived from numerical analyses to the tensile strength of intact rock. Given that the rock mass is relatively homogeneous and artificial damage (e.g., blasting-induced damage) can be neglected, as in the Horonobe Underground Research Laboratory, the MSI model is likely to be applicable in estimating the highest potential hydraulic conductivity in the EDZ.

Hydraulic performance of anionic polymer-treated bentonite-granular soil mixtures

Abstract In this study, hydraulic conductivity and viscosity determination tests were performed on two different bentonite-granular soil mixtures having various amounts of bentonite in order to obtain the optimum mixture to be used as a liner for waste containment facilities. To enhance the hydraulic capability of these mixtures, an anionic polymer was added to the bentonite. In bentonite-granular soil mixtures, two different aggregate compositions were used: A typical aggregate composition used in the production of C20 type concrete with a void ratio of 0.33 and an aggregate composition with a void ratio of 0.21 that was the minimum void ratio determined by testing various granular soil compositions. In these two mixtures, the bentonite content varied from 8 to 15% whereas the polymer content was within the range of 0.5–10% by mass. Test results indicated that intrinsic permeability decreased drastically due to an increase in the bentonite content. 15% bentonite addition caused a decrease of almost 5.5 orders of magnitude when compared with the granular soils without any bentonite content. 2% anionic polymer addition resulted in a decrease of approximately 2.5 orders of magnitude in hydraulic conductivity. However, further increase in polymer content had almost no effect on lowering hydraulic conductivity. 2% polymer addition in bentonite-granular soil mixtures provided hydraulic conductivity values as low as 10−11 m/s. The decrease in hydraulic conductivity was attributed to the increase in the viscosity of the fluid. Due to polymer addition, an inverse relationship existed between hydraulic conductivity and intrinsic permeability. As a result, polymer-treated bentonite-granular soil mixtures can effectively be used as barrier layers in waste containment facilities.

The hydraulic conductivity of sediments: A pore size perspective

This article presents an analysis of previously published hydraulic conductivity data for a wide range of sediments. All soils exhibit a prevalent power trend between the hydraulic conductivity and void ratio. Data trends span 12 orders of magnitude in hydraulic conductivity and collapse onto a single narrow trend when the hydraulic conductivity data are plotted versus the mean pore size, estimated using void ratio and specific surface area measurements. The sensitivity of hydraulic conductivity to changes in the void ratio is higher than the theoretical value due to two concurrent phenomena: 1) percolating large pores are responsible for most of the flow, and 2) the larger pores close first during compaction. The prediction of hydraulic conductivity based on macroscale index parameters in this and similar previous studies has reached an asymptote in the range of kmeas/5≤kpredict≤5kmeas. The remaining uncertainty underscores the important role of underlying sediment characteristics such as pore size distribution, shape, and connectivity that are not measured with index properties. Furthermore, the anisotropy in hydraulic conductivity cannot be recovered from scalar parameters such as index properties. Overall, results highlight the robustness of the physics inspired data scrutiny based Hagen–Poiseuille and Kozeny-Carman analyses.

Phosphate-amended sand/Ca-bentonite mixtures as slurry trench wall backfills: Assessment of workability, compressibility and hydraulic conductivity

In regions and countries where sodium bentonite is scarce, the resourceful calcium bentonite can be considered as an alternative material for soil-bentonite slurry trench walls. However, the lower swelling capacity of calcium bentonite as compared to Na-bentonite may result in the unacceptable high hydraulic conductivity of the sand/calcium bentonite backfills, and, therefore, amendment of calcium bentonite is necessary. However, studies on the feasibility of using amended calcium bentonite for soil bentonite backfills are limited. This study investigates the feasibility of using sodium hexametaphosphate amended calcium bentonite for the backfill material through a comprehensive laboratory investigation. First, a series of viscosity, density and filtrate loss tests are conducted using bentonite-tap water slurries with different amounts of phosphate to determine the optimal amendment dosage. Subsequently, the Atterberg limits and free swell index are evaluated for the amended/un-amended calcium bentonite and backfills, which consist of sand and amended/un-amended calcium bentonite. Finally, slump, oedometer tests and flexible-wall hydraulic conductivity tests are conducted on the backfills. The results indicate that the slurry with 20% calcium bentonite amended by 2% phosphate results in the target slurry, and the optimum phosphate dosage for amended calcium bentonite is found to be 2%. The phosphate amendment causes an increase of 1.21 times in the liquid limit, and an increase of 1.40 times in the free swell index of the amended bentonite relative to those of the un-amended bentonite. The sand/calcium bentonite backfill changes from non-plasticity to plasticity after the amendment. The amended backfill displays two times higher swell index value and one order of magnitude lower consolidation coefficient value than the un-amended backfill. The hydraulic conductivity of un-amended backfills containing 15% to 25% un-amended bentonite is greater than the commonly targeted value of 10−9m/s for slurry trench walls. In contrast, the hydraulic conductivity of the amended backfill with 15% to 25% amended bentonite varies from 8.3×10−10m/s to 2.7×10−10m/s, which is lower than 10−9m/s. In addition, the amended backfills containing 20% and 25% amended calcium bentonite have nearly the same magnitude of hydraulic conductivity as the conventional sand/sodium bentonite backfill. This study demonstrates that phosphate is a promising amendment for achieving low hydraulic conductivity of sand/calcium bentonite backfills for soil-bentonite slurry trench walls.

Applicability of thermal response tests in designing standing column well system: A numerical study

The thermal performance of a standing column well system is sensitive to geological and hydrogeological conditions and is maximized in the conditions of stable groundwater temperature, high well yield, and shallow water level. Intricate heat transfer phenomena in the standing column well system leads to difficulties in establishing unified detailed guidelines for the design, installation, and operation of the standing column well system, and consequently a variety of guidelines exist in different countries. According to the guidelines for the design, installation, and operation of a standing column well system, thermal response tests are conducted in Korea and thermal properties such as thermal conductivity and thermal diffusivity which are essential for the design step are obtained. This article investigated the applicability of thermal response tests in the design of a standing column well system based on a numerical study. Based on the developed standing column well model, a total of 420 scenarios were simulated by varying the thermal, hydraulic, and operation properties, and bleeding rates to evaluate their effects on an enhanced factor. The results show that the applicability of thermal response tests in designing a standing column well system mainly depends on the magnitude of hydraulic conductivity.

Examining Freeze/Thaw Cycling and Its Impact on the Hydraulic Performance of Cement-Treated Silty Sand

AbstractCement-based solidification/stabilization (s/s) is a remediation technology that has been widely used for treatment of a range of contaminants. Currently, there is limited published data on changes in hydraulic performance of cement-treated materials subjected to cycles of freezing/thawing (f/t). Fourteen sets of tests were performed to examine the influence of factors such as number of f/t cycles, freezing temperature, curing time, and mix design on changes in hydraulic conductivity and unconfined compressive strength (UCS) of cement-treated silty sand. Results showed an increase of up to three orders of magnitude in hydraulic conductivity as well as decreases in UCS values after exposure to 4 and 12 f/t cycles. Analysis of variance (ANOVA) performed on the results of a factorial experiment considering the effect of freezing temperature, curing time, and number of f/t cycles showed that all of these factors are significant in affecting the measured changes in the hydraulic conductivity and UCS v...

The role of the exopolysaccharides in enhancing hydraulic conductivity of biological soil crusts

Biological soil crusts (BSCs) are highly specialized topsoil microbial communities commonly found in arid and semiarid environments, permeated by a polymeric matrix of polysaccharides. BSCs can in principle influence edaphic properties such as texture, pore formation and water retention, which in turn determine water distribution and biological activity in dry lands. This paper investigates the influence of biotic and abiotic factors on BSC hydraulic conductivity, a parameter gauging the ease with which water can move through the pore spaces. Texture, phototroph abundance, microbial composition, and extracellular carbohydrate content were considered as potentially relevant parameters in a correlational study of BSC samples that spanned 1.5 orders of magnitude in hydraulic conductivity. A newly developed, non-destructive extraction method enabled us to directly quantify the specific role of extracellular polysaccharides on soil permeability on a variety of samples. Hydraulic conductivity showed a strongest correlation with texture (positive with sand content, negative with silt and clay). A weaker negative correlation with carbohydrate content, especially with polysaccharides having a molecular weight < 100 kDa, was also detected. In multiple regression analyses texture (silt content) was sufficient to explain most of the variation in hydraulic conductivity However, experimental removal of polymeric carbohydrates, resulted invariably in a substantial decrease in hydraulic conductivity for any given sample (between 1.7 and 3.3 fold). Our results suggest that while soil texture determines overall hydraulic conductivity in BSCs, the presence of exopolysaccharides can significantly enhance it, likely by conferring a spongy structure to a BSC thus increasing the number of waterways within it.

The physical scale modelling of braided alluvial architecture and estimation of subsurface permeability

ABSTRACTThe quantitative modelling of fluvial reservoirs, especially in the stages of enhanced oil recovery, requires detailed three‐dimensional data at both the scale of the channel belt and within‐channel. Although studies from core, analogue outcrop and modern environments may partially meet these needs, they often cannot provide detail on the smaller‐scale (i.e. channel‐scale) heterogeneity, frequently suffer from limited three‐dimensional exposure and cannot be used to examine the influence of different variables on the process–deposit relationship. Physical modelling offers a complementary technique that can address many of these quantitative requirements and holds great future potential for integration with reservoir modelling. Physical modelling provides the potential to upscale results and derive reservoir information on three‐dimensional facies geometry, connectivity and permeability.This paper describes the development and use of physical modelling, which employs generic Froude‐scaling principles, in an experimental basin that permits aggradation in order to model the morphology and subsurface depositional stratigraphy of coarse‐grained braided rivers. An example is presented of a 1:50 scale model based on the braided Ashburton River, Canterbury Plains, New Zealand and the adjacent late Quaternary braided alluvium exposed in the coastal cliffs. Critically, a full, bimodal grain size distribution (20% sand and 80% gravel) was used to replicate the prototype, which allows the realistic reproduction of the surface morphology and importantly permits grain size sorting during deposition. Uncertainties associated with the compression of time, sediment mass balance and the hydrodynamics of the finest particle sizes do not appear to affect the reproducibility of stratigraphy between experimental and natural environments.Sectioning of the preserved sedimentary sequence in the physical model allows quantification of the geometry, shape, spatial distribution and internal sedimentary structure of the coarse‐ and fine‐grained facies. A six‐fold facies scheme is proposed for the model braided alluvium and a direct link is established between the grain size distribution and facies type: this allows permeability to be estimated for each facies, which can be mapped onto two‐dimensional vertical cross‐sections of the preserved stratigraphy. Results demonstrate the dominance of four facies based on permeability that range over three orders of magnitude in hydraulic conductivity. Quantification of such variability, and linkage to both vertical proportion curves for facies distribution and connectivity presents significant advantages over other methodologies and offers great potential for the modelling of heterogeneous braided river sediments at the within channel‐belt scale. This paper outlines how physical models may be used to develop high‐resolution, geologically‐accurate, object‐based reservoir simulation models.

Interpretation of Seismic Piezocone Results for the Estimation of Hydraulic Conductivity in Clays

Abstract Seismic piezocone penetration tests with dissipation phases provide sufficient data for outlining the geostratigraphy, soil strength, stiffness, and flow characteristics in fine-grained soils. The dissipation of excess pore water pressures with time can be monitored at regular intervals (e.g., at 1-m rod breaks) and provides information on the coefficient of consolidation (ch). Monotonic and/or dilatory responses of Δu decay can be accommodated. The shear wave velocity (Vs) provides a measure of the small-strain stiffness (G0), or surrogate evaluation of the constrained modulus (D′). A sampling of data from ten clay sites was used to assess the derived magnitude of hydraulic conductivity, as determined from k = chγw/D′.

NUMERICAL EXPERIMENT ON THE RELATIONSHIP BETWEEN SOIL PERMEABILITY AND LONG-TERM BEHAVIOR OF BASE-FLOW

Numerical experiments were carried out to investigate the relationship between the reduction curves of base-flow and the permeability of soil layer at hill-sloped forest. Variable parameters of the experiments were only saturated hydraulic conductivities in the direction of the hill slope and the normal direction.In the results, the peaks of the base-flow were controlled by the magnitude of hydraulic conductivities in the both directions and arrival times in the peak base-flow were governed by the magnitude of hydraulic conductivity in the normal direction to the soil surface. The results also showed that the shapes of the base-flow recession curves could be controlled by the magnitude of hydraulic conductivities in the direction of hill-slope.

Scale Dependency of Hydraulic Conductivity Measurements

AbstractThe hydraulic conductivity of five stratigraphic units in a carbonate aquifer has been measured with slug, pressure, and pumping tests, and with two calibrated digital models. The effective test radii range from less than one to greater than 10,000 meters. On log‐log plots hydraulic conductivity increases approximately linearly with test radius to a range between 20 and 220 meters, but thereafter, it is constant with scale.The increase in magnitude of hydraulic conductivity is similar to scaling effects reported at seven additional sites in a variety of geologic media. Moreover, the increase in magnitude correlates with an increase in variance of log‐hydraulic conductivity measured at successively greater separation distances.The rate of increase in both parameters, and particularly the range, have characteristic values for different pore systems. The larger ranges are consistently present in units with greater secondary porosity. Therefore, scaling effects provide a qualitative measure of the relative importance of secondary and primary permeability, and they can potentially be used to distinguish the dominant type of pore system.

Simultaneous inversion of hydrogeologic and thermal data: 2. Incorporation of thermal data

Introduction of a data set for a second potential field provides an approach to deal with data limitations in the inverse problem. We examine how temperature measurements can be used to improve the resolution of model parameters in constructing a model of a steady state groundwater flow system. The approach is applicable to cross‐sectional models with vertical components of fluid flow. In media with low hydraulic conductivity, the thermal regime is conductive and temperature measurements do not carry direct information on the hydrogeologic regime. In more permeable systems however, fluid velocities are sufficient to redistribute heat within the basin, perturbing the conductive regime. Parameter estimates developed in the inverse simulation are required to satisfy a weighted measure of both the hydrogeologic and thermal data. The effectiveness of this joint inverse depends upon the extent of the advective disturbance, which, in turn, is controlled by the magnitude of hydraulic conductivity, the length scale and location of hydraulic conductivity variations, the depth of active flow, and the regional configuration of the groundwater flow system. A series of hypothetical examples are presented to demonstrate how model misfit can be reduced when noisy hydraulic head data are augmented with thermal data. Because the extent of an advective disturbance depends upon the absolute value of hydraulic conductivity, addition of temperature measurements in an inverse simulation is particularly helpful in cases where there is uncertainty in boundary conditions, such as recharge rates. The approach is used to construct a model of the groundwater flow system at Downie Slide, north of Revelstoke, British Columbia. Results presented in part one suggest that the slide behaves as a homogeneous, isotropic medium (Woodbury et al., 1987). With a homogeneous hydraulic conductivity, only the ratio of fluid flux to hydraulic conductivity could be determined. By including thermal data, the value of hydraulic conductivity can be estimated.