Hydraulic Conductivity Coefficient Research Articles

Solution methods of hydraulic conductivity in low permeable saturated soil during liquid releasing

Solution methods of hydrogeological parameters in saturated zones for certain geological behaviors have been presented in many studies. Traditional solution methods of hydrogeological parameters, such as hydraulic conductivity and storage coefficient, were acquired by in situ hydrogeological experiment or seepage control equations. However, those two methods obtain a constant value of hydrogeological parameters which is not very suitable in practical cases. This study assumes that hydrogeological parameters to be a variable value because the properties of soil were changed during liquid releasing. An analytical solution for liquid releasing from saturated soil was deduced based on the existing seepage control equation, and the analytical value of hydrogeological parameters was obtained. Moreover, analytical expression for hydraulic conductivity was developed, and variable hydraulic conductivity was gained by analyzing flow quantity during seepage. Different calculation methods were used to get constant and variable conductivity coefficient, respectively. A laboratorial test model of saturated soil under designed conditions was also established to verify the analytical solutions of both constant and variable parameters by fitting the calculated value and measured value curve. Seepage tests and case studies showed that variable hydraulic conductivity value presents higher agreement with the measured data for flux versus time than constant hydraulic conductivity. In order to prove the fact that variable parameter is more reasonable in real cases, we also conducted a group of comparative tests by rising and falling the hydraulic head of seepage model in three periods. Three different hydraulic conductivities were obtained, and then they were substituted to seepage equation for the sake of curve fitting. The correlation coefficient between measured flow versus time curve (obtained from hydraulic conductivity vs. time curve) and calculated flow versus time curve is higher than flow versus time obtained from hydraulic conductivity versus periods. Solution methods suggested in this paper are generally applicable to problems involving the hydraulic conductivity, specific storage and other related hydrogeological parameters calculation of low permeable saturated soil.

Hydraulic Conductivity of Residual Soil-Cement Mix

In Malaysia, although there are several researches on engineering properties of residual soils, however study on the hydraulic conductivity properties of metasedimentary residual soils is still lacking. Construction of containment walls like slurry wall techniques can be achieved with hydraulic conductivity of approximately 5 x 10-7cm/sec. The objectives of the study were to determine the physical properties of metasedimentary residual soils and to determine the influence of 1%, 3%, 5% and 10% of cement on hydraulic conductivity parameters. The coefficient of hydraulic conductivity of the soil naturally and soil-cement mixtures were determined by using the falling head test. According to the test, the hydraulic conductivity of the original soil was 4.16 x 10-8 m/s. The value decreases to 3.89 x 10-8 m/s, 2.78 x 10-8 m/s then 6.83 x 10-9 m/s with the addition of 1%, 3% and 5% of cement additives, respectively. During the hydration process, cement hydrates is formed followed by the increase in pH value and Ca(OH)2 which will alter the modification of pores size and distribution. When the quantity of cement increases, the pores size decrease. But, the addition of 10% cement gives an increased hydraulic conductivity value to 2.78 x 10-8 m/s. With 10%, the pore size increase might due to flocculation and agglomeration reaction. The generated hydraulic conductivity values will indirectly become a guide in the preliminary soil cement stabilization to modify the properties of the soil to become more like the properties of a soft rock.1. Introduction

A quadruple-porosity model for shale gas reservoirs with multiple migration mechanisms

This paper presents a quadruple-porosity model for multi-stage fractured horizontal well (MFHW) with finite conductive hydraulic fractures in shale gas reservoirs. In this model, free gas, adsorbed gas and dissolved gas co-exist and gas migration in shale incorporates diffusion in kerogen bulk, desorption from the surface of organics and clays, slippage flow in porous kerogen and inorganic matrix, and Darcy flow in natural fractures. Bi-Langmuir theory was introduced to describe gas desorption from the surface of clays and organics. Continuous line source function, Laplace transform and numerical discrete method were employed to solve this new model. Gauss-Jordan elimination method and Stehfest numerical inversion algorithm were applied to calculate the pressure and production responses. Type curves were plotted and flow regimes were identified. Sensitivity analysis of solubility coefficient, diffusion coefficient, inter-porosity coefficient, TOC, clays content, hydraulic fracture conductivity and permeability correction coefficient was performed. Finally, the proposed model was validated by fitting actual production data of a field case and comparing with other models. The matching results showed that quadruple porosity model considering dissolved gas was closer to the actual situation than trilinear-flow model and dual-porosity radial-flow model. To sum up, this presented model considering some key mechanisms further expands the transient pressure models for MFHW in shale gas reservoirs and it can be utilized to analyze well performance in the production life of gas wells.

Utilization of spilitic mining wastes in the construction of landfill bottom liners

In the present research work the possibility of spilite valorization, a mining waste produced during the exploitation of nickeliferous laterites from LARCO Mining and Metallurgical Company, as an alternative material for the construction of compacted landfill liners was examined. For that purpose, different types of mixtures were tested with bentonite content up to 3wt%. Particle size distribution, chemical analysis, mineralogical analysis by X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG) and microstructure examination by scanning (SEM) and transmission (TEM) electron microscopy were used for the spilitic sand characterization. The evaluation of the produced spilitic sand-bentonite mixtures was carried out by determining the liquid limit (WL), the plasticity index (PI), the organic matter content, the Proctor compaction and the hydraulic conductivity. According to the results, the hydraulic conductivity coefficient of the mixture with 3wt% bentonite addition was less than 10−9m/s, satisfying the requirement for landfill liner materials.

Modelling water content redistribution during evaporation from sandy soil in the presence of water table

An analytical model based on Richards equation is presented to describe water content redistribution during evaporation. Exponential functions are utilized to describe the relation of hydraulic conductivity and water content on pressure head. The water content at any given depth z and time t, together with the evaporation rate at the soil surface are outputs of this model. The proposed is capable of modelling the transformation of the constant rate stage into a falling rate stage of evaporation, moreover it extends the use of analytical model to arbitrary initial conditions. Detailed parametric analysis was carried out to investigate the effect of six governing factors. The main findings are as follows: hydraulic conductivity (Ks) and desaturation coefficient (α) affect the water content profile more than the storage capacity (θs-θr) does; the relation between the duration of the constant rate stage and the dimensionless evaporation rate γ can be expressed by a negative power function; the initial conditions are the most influential factor for the soil water profile among all factors examined. Finally, two evaporation tests conducted on K-7 sand and Fontainebleau sand were introduced to validate the proposed analytical model. Results showed that this model could reasonably predict the temporal water content profile during evaporation process, but some discrepancies still existed in some cases. Nevertheless, the analytical model provides a useful tool for predicting the vertical distribution of water content during evaporation.

Estimation of Hydraulic Conductivity from Grain Size Distribution: A Case Study of Sediments From Panzara River, Tapi Basin, Northern Maharashtra (India)

The aim of this work was to determine the grain size of the sediments and estimation of hydraulic conductivity. A total 20 sediment samples were collected from 13 different locations from both the bank of Panzara river channel, Dhule district (Maharashtra). Geologically, this region belongs to Deccan Volcanic Province of upper Cretaceous to lower Eocene age. Weight percentage frequencies and cumulative weight percentage frequencies of the sediment samples were computed. The grain size parameters like graphic mean (Mz), graphic standard deviation (ϭ 1), graphic skewness (SK) and graphic kurtosis (KG) were also computed. The coefficient of curvature (Cc), coefficient of uniformity (Cu) and hydraulic conductivity (Hc/K) were also calculated. The grain size results showed that sediments are moderate to poor sorted.

A FRACTIONAL FUZZY SIMULATION METHOD FOR PREDICTING DISSOLVED TOLUENE AND OXYGEN CONCENTRATIONS IN AQUIFERS UNDER MICROBIAL ATTENUATION

This study proposes a modified fractional fuzzy simulation (MFFS) method to predict the toluene and oxygen concentrations in aquifers under microbial attenuation conditions. The method integrates the modeling of groundwater flow contaminant transport and fuzzy parameters analysis within a general framework. Compared to conventional fractional fuzzy simulation (FFS), decreased interior points of fuzzy parameters need to be used, thus reducing the simulation time. The method is applied to an aquifer of the Pinggu site in Beijing, China, where three parameters (i.e. longitudinal dispersivity, hydraulic conductivity and storage coefficient) are represented as fuzzy sets. Results from the case studies demonstrate that i) hydraulic conductivity has the most significant effect on toluene concentrations, while longitudinal dispersivity is rather significant, and storage coefficient has no apparent effect. ii) longitudinal dispersivity has the most significant effect on oxygen concentrations, while hydraulic conductivity is rather significant, and storage coefficient has no apparent effect. It is also observed that iii) the method is useful for not only site simulation, but also risk assessment, remediation design and process control under parameter uncertainty.

Developing Groundwater Variability Probes and Wireless Sensor Networks for Characterizing the Subsurface Low Flow Field

Groundwater monitoring plays a key role in understanding solute transport processes, including pollutant fate and transport mechanisms, detection of leaks from groundwater storage containers, and development of early warning systems for flooding and bank stability. Furthermore, incorporating these monitoring fields into remote stations with wireless data transmittal has proven useful in real-time data analysis and field forecasting. A promising new technology called the groundwater variability probe (GVP) was developed, tested, and integrated into a wireless field station with inclusion of soil moisture probes and pressure transducers for monitoring hydraulic conditions within a pond bank. The GVP is capable of measuring real-time centimeter-scale velocity magnitude, flow direction, hydraulic conductivity, and dispersion coefficient measurements simultaneously. We found that the GVP can effectively measure seepage velocity in dispersion-dominated regimes from 26 to 460 cm ${\rm day}^{\mathrm {{-1}}}$ range and flow direction to within ±10°. The hydraulic conductivity was determined using Darcy's law. The GVP-derived velocity measurements were found to be within expected ranges of hydraulic conductivity. Dispersion coefficients of the plume were derived and found to be similar to values reported in the literature. A wireless sensor network was installed on a wet retention pond bank, allowing remote real-time access for monitoring changes in soil moisture, groundwater velocity, and stage fluctuations, providing insights into correlations with in-situ storm events.

Anisotropic hydraulic conductivity and critical hydraulic gradient of a crushed sandstone–mudstone particle mixture

ABSTRACTThis paper describes the development of a modified instrument used to measure the anisotropic hydraulic conductivity of coarse soils. Then, based on this modified instrument, horizontal and vertical hydraulic conductivities and critical hydraulic gradients of a crushed sandstone–mudstone particle mixture are measured. Using this data, we investigate the effects of particle size on the anisotropic hydraulic conductivity. The testing results indicate that the anisotropic hydraulic conductivity coefficient, which is defined as the logarithm value of the ratio of the horizontal hydraulic conductivity to the vertical conductivity, ranges from 0.079 to 0.358. This means the horizontal hydraulic conductivity is 1.20 to 2.28 times to that of the vertical conductivity. The anisotropic coefficient decreases as the uniformity coefficient increases. Meanwhile, the critical hydraulic gradient increases with an increase in fine particle content.

Characteristics of groundwater seepage with cut-off wall in gravel aquifer. II: Numerical analysis

This paper presents a numerical investigation into the leakage behavior of cut-off walls in gravel strata due to dewatering in a deep excavation pit. The calculated values of the groundwater head and surface settlement using a model agree well with the measured values. Values of the hydraulic conductivity (k) and storage coefficient (Ss) of each soil layer are obtained from the test results when the cut-off wall is 43 m deep. The leakage through the cut-off wall in gravel is analyzed by considering a variation in hydraulic conductivity in different sections of the cut-off wall. The simulated results show that a significant leakage occurred in the 54 m deep cut-off wall. Although leakage did occur in the full cut-off wall in the confined aquifer, the full cut-off wall is still more efficient in preventing groundwater seepage than the partial cut-off wall. The relative depths of the cut-off wall and of the wells have a significant effect on ground surface settlement during the withdrawal of groundwater. Therefore, the appropriate selection of relative depth of both cut-off wall and pumping well is an effective way of controlling surface settlement outside the pit.

Compost addition reduces porosity and chlordecone transfer in soil microstructure.

Chlordecone, an organochlorine insecticide, pollutes soils and contaminates crops and water resources and is biomagnified by food chains. As chlordecone is partly trapped in the soil, one possible alternative to decontamination may be to increase its containment in the soil, thereby reducing its diffusion into the environment. Containing the pesticide in the soil could be achieved by adding compost because the pollutant has an affinity for organic matter. We hypothesized that adding compost would also change soil porosity, as well as transport and containment of the pesticide. We measured the pore features and studied the nanoscale structure to assess the effect of adding compost on soil microstructure. We simulated changes in the transport properties (hydraulic conductivity and diffusion) associated with changes in porosity. During compost incubation, the clay microstructure collapsed due to capillary stresses. Simulated data showed that the hydraulic conductivity and diffusion coefficient were reduced by 95 and 70% in the clay microstructure, respectively. Reduced transport properties affected pesticide mobility and thus helped reduce its transfer from the soil to water and to the crop. We propose that the containment effect is due not only to the high affinity of chlordecone for soil organic matter but also to a trapping mechanism in the soil porosity.

Analytical sensitivity analysis of transient groundwater flow in a bounded model domain using the adjoint method

AbstractSensitivity analyses are an important component of any modeling exercise. We have developed an analytical methodology based on the adjoint method to compute sensitivities of a state variable (hydraulic head) to model parameters (hydraulic conductivity and storage coefficient) for transient groundwater flow in a confined and randomly heterogeneous aquifer under ambient and pumping conditions. For a special case of two‐dimensional rectangular domains, these sensitivities are represented in terms of the problem configuration (the domain size, boundary configuration, medium properties, pumping schedules and rates, and observation locations and times), and there is no need to actually solve the adjoint equations. As an example, we present analyses of the obtained solution for typical groundwater flow conditions. Analytical solutions allow us to calculate sensitivities efficiently, which can be useful for model‐based analyses such as parameter estimation, data‐worth evaluation, and optimal experimental design related to sampling frequency and locations of observation wells. The analytical approach is not limited to groundwater applications but can be extended to any other mathematical problem with similar governing equations and under similar conceptual conditions.

Evaluation of the effects of the radial constant-head boundary in slug tests

A semianalytical model of slug tests, conducted in a completely penetrating well within a radial constant-head boundary, was derived. The model, based on the Cooper et al. (1967) model, estimates the hydraulic conductivity and storage coefficient through the matching of type curves. Type curves of the semianalytical solution were plotted, and the effect of the distance of the radial constant-head boundary is discussed. For different storage coefficients, the critical distances of the effect of the constant-head boundary were determined. The effect of the storage coefficient on the response of the water head in slug tests with a radial constant-head boundary of a certain distance is also shown. To verify the model, laboratory slug-test experiments were carried out using a cylindrical test platform, in which an artificial confined coarse-sand aquifer was built. Pumping tests were also executed using the test platform. The Cooper et al. (1967) model and new semianalytical model were used to analyze measurements; the hydraulic conductivity and storage coefficient determined using the two methods were compared to demonstrate the importance of the radial constant-head boundary. A model considering the inertial effect was also used to analyze the slug-test measurements, and although the water head response did not oscillate greatly, the inertial effect affected the slug-test calculation result. The laboratory experiments indicate that the proposed semianalytical model is reasonable and reliable. Cooper HH, Bredehoeft JD, Papadopulos IS (1967) Response of a finite-diameter well to an instantaneous charge of water, Water Resour Res 3(1):263–269.

Formulation of an Optimal Mix Design of Stabilized Peat Columns with Fly Ash as a Pozzolan

As a foundation soil, peat poses a grave threat to civil engineering construction due to its softness and large compressibility in nature. Hence, it is crucial to research on its cementation mechanism, so that relevant materials can be quantified to stabilize the soil. In this research work, fly ash (FA) was utilized as a pozzolan to enhance the long-term strength accumulation of stabilized peat columns at experimental scale. The research focus was primarily centered on the design of a suitable mixture of Portland composite cement (PCC), calcium chloride (CaCl2), FA and silica sand that can be applied for the development of stabilized peat columns. A laboratory-based approach was initiated to investigate the pertinent factors that influenced unconfined compressive strength of the stabilized peat. It was found that stabilization of peat can be optimally achieved with a mix design at 10 % partial replacement of PCC with FA. The engineering performance of the stabilized peat was assessed by performing unconfined compression and permeability tests. There were progressive patterns of increase in unconfined compressive strength and decrease in coefficient of hydraulic conductivity for test specimens formulated at the optimal mix design. Chemical and morphological evidences on cementation effect and pore reduction in the peat stabilization are traceable from the respective X-ray diffraction and scanning electron microscopy results. A key discovery is that water continued to play a role as a cement dissolving agent that triggered reactivity with FA to precipitate cementing crystals for the binding of the stabilized peat.

Quantitative assessment of groundwater pollution intensity on typical contaminated sites in China using grey relational analysis and numerical simulation

Groundwater vulnerability assessment is an important method for groundwater pollution risk assessment. However, vulnerability assessment results rarely consider groundwater pollution concentration. Few quantitative studies consider groundwater pollutant concentration in different hydrogeological conditions. HYDRUS-1D software can simulate different concentrations of pollutants reaching the shallow aquifer under some vadose zone conditions. However, HYDRUS-1D simulation parameter settings are complicated; thus, it is difficult to simulate groundwater pollution intensity (GPI) on the site with limited information. In this study, the issue of site data constraints for model predictions is solved. Ammonia–nitrogen is selected as an indicator, and a method for quantitative groundwater pollution assessment based on grey relational analysis (GRA) is proposed. According to two factors (inherent, extrinsic) of groundwater vulnerability assessment, and on the basis of the information from 18 contaminated sites, primary GPI control factors, including emission concentration, hydraulic conductivity, soil density and diffusion coefficient, are filtered using GRA. These four factors are utilized as variables to establish a multiple linear regression (MLR) equation, which is used to predict the GPI of polluted sites. Compared with a HYDRUS-1D simulation, the proposed GPI prediction method can effectively predict GPI with simpler input conditions. The established MLR equation satisfies a significance test and small error analysis. Comparative results between simulation values and regression values on the established case show that the regression values are closer to the measured value. Hence, the MLR equation is practical and can be applied for sensible groundwater source management and land use planning.

Assessing the potential of biochar and charcoal to improve soil hydraulic properties in the humid Ethiopian Highlands: The Anjeni watershed

Biochar has shown promise for restoring soil hydraulic properties. However, biochar production could be expensive in the developing world, while charcoal is widely available and cheap. The objective of this study is therefore to investigate whether some of the charcoal made in developing countries can also be beneficial for improving soil hydraulic properties, and explore whether charcoal could potentially restore the degraded African soils. Laboratory and field experiments were conducted in the Anjeni watershed in the Ethiopian highlands, to measure soil physical properties including soil moisture retention and infiltration rates. Soils were dominantly clayey with pH in the acidic range, low organic carbon content, and steady infiltration rates ranging between 2 and 36mm/h. Incorporation of woody feedstock (Acacia, Croton, and Eucalyptus) charcoals significantly decreased moisture retention at lower tensions (10 and 30kPa), resulting in an increase in relative hydraulic conductivity coefficients at these tensions. While wood (oak) biochar decreased moisture retention at low tensions, corn biochar increased retention, but effects were only slight and not significant. Surprisingly, available water content was not significantly affected by any of the amendments. Overall findings suggest that wood charcoal amendments can improve soil hydraulic properties of degraded soils, thereby potentially reducing runoff and erosion.

Physical and mathematical model of raw mixture agglomeration process using local fuels

Within the work, carried out in the Republic of Belarus on the implementation of the state program "Peat", physico-mathematical model of the raw mixture agglomeration using local fuels was developed, the directions necessary to implement the plan of increasing the peat use for energy purposes were identified. Physico-mechanical properties of raw materials and fuel briquettes, the elemental composition of the peat, the main technical parameters of the peat crusher were presented. Fractional composition of fuel based on fuel briquettes after the first and second crushing was determined. The mathematical models for determining the hydraulic conductivity coefficient were developed, and the influence of different contents of loam, fragmented peat and coal in a mixture on the aggloporite strength was determined. The dependences of aggloporite strength on its density when adding crushed briquettes and sawdust in the obtained experimental batch were defined. Application of the above techniques has allowed to get the economic effect at the MCMP of more than 100 million BYR (approx. 10 000 USD) at the release of the experimental batch of aggloporite.

Individual landslide hazard assessment of natural valleys and slopes based on geotechnical investigation and analysis

Slope failures caused by rainfall on weathered granite are common occurrences in many parts of the world and it is more severe in Japan where there are a significant number of slopes susceptible to failure. At present, about 31,987 natural, and valley slopes are found to be susceptible to landslide disasters in Hiroshima Prefecture, the highest number of any prefecture in Japan. In Hiroshima Prefecture, the prefectural land is divided into 350 units of 5km2, and the hazard of each unit was assessed based on the rainfall data and past records of failures. However, the existing hazard assessment system was found not to be adequate of making better predictions of individual failures in the region, and moreover the system was developed without carrying out any reliable slope stability analyses. In this study, an attempt has been made to understand the mechanism of individual slope failure through seepage analyses and stability analyses. A series of laboratory model tests were conducted to develop the relationships among volumetric water content, degree of saturation, suction, and coefficient of hydraulic conductivity under unsaturated conditions. Field investigation and laboratory tests were conducted based on the four valleys which were identified as potentially hazardous zones in Higashi-Hiroshima city in Hiroshima Prefecture. Graphical relationships were developed among the volumetric water content, suction, rainfall intensity, coefficient of hydraulic conductivity, and degree of saturation for Masado soils. Based on the relationships developed, suction was calculated along the soil profile of natural valleys with the lapse of time. Thus, shear strength parameters were determined based on the degree of saturation calculated from the data of volumetric water contents. The stability analyses revealed that the factor of safety gradually decreases with the formation of High Moisture Content Belt (HMCB) and drastically reduces with the formation of the water table. The susceptibility of failure for each of the four valleys is given based on the hazard assessment system, and is compared and discussed.

Impacts of transport mechanisms and plume history on tailing of sorbing plumes in heterogeneous porous formations

This work investigated the impacts of permeability and sorption heterogeneity on contaminant transport in groundwater using simulation experiments designed to elucidate the causes of tailing. The effects of advection, diffusion and sorption mechanisms and plume history were explored. A simple conceptual model consisting of a single inclusion (heterogeneity) of uniform hydraulic conductivity K and sorption distribution coefficient Kd was adopted. The 3D inclusion, shaped as a horizontal oblate ellipsoid of variable thickness, was placed in a homogeneous anisotropic background of different hydraulic conductivity and sorption distribution coefficient. The background represents average K and Kd of a heterogeneous porous formation. A closed-form analytic flow solution for uniform flow past the inclusion was coupled with a numerical transport solution to simulate contaminant migration for a wide range of transport parameters and two distinct source conditions. Over 2600 numerical simulations were performed in parallel. Transport results were presented in terms of travel time distributions at a control plane downstream of the inclusion and used to quantify tailing for a wide range of transport parameters, in order to separate advection-dominated from diffusion-dominated transport regime and to investigate effects of inclusion shape, diffusion, sorption and plume history on tailing.

Estimating coefficient of consolidation and hydraulic conductivity from piezocone test results - Case studies

The methods for estimating in-situ hydraulic conductivity (khp) and coefficient of consolidation (chp) in the horizontal direction from piezocone penetration and dissipation test results have been investigated using test results at two sites in Saga, Japan. At the two sites the laboratory values of hydraulic conductivity (kv) and coefficient of consolidation (cv) in the vertical direction are also available. Comparing khp with kv and chp with cv values, suitable methods for estimating khp and chp values are recommended. For the two sites, where khp ≈ kv and chp ≈ 2cv. It is suggested that the estimated values of khp and chp can be used in engineering design.