1-Dimensional numerical modelling of unsaturated water flow and oxygen diffusion in overburden material column using hydrus 1-D

Coal mining activities, especially overburden material dumping can cause a negative impact into the environment, i.e., acid mine drainage, Acid mine drainage is characterized as low pH water with high sulphate and metal content produced from sulphidic-bearing overburden material with oxygen and water. In unsaturated condition, both of gaseous and water phases exist, acid mine drainage is generated. This study aims to characterize and model the water content in unsaturated condition and diffusion of oxygen of overburden material using the Hydrus 1-D software in a laboratory-scaled column. Laboratory-scaled column is initially filled with 75-cm height of dry overburden material and subjected into 5-cm constant head water level at the top of the column with free-flow condition at the bottom of column. The modelling result shows the water content of overburden material varies within depth and time elapsed and is saturated between 32400 minutes and 36000 minutes after initial wetting. Diffusivity of oxygen is linearly correlated with the water content of the overburden material at any given time and depth that varies between 1.34 × 10−7 m2/s and 8.80 × 10−12 m2/s. Water content and diffusivity of oxygen is expected to affect the generation of acid mine drainage in the overburden material.

Development of a Model for Predicting the Volatilization Flux from Unsaturated Soil Contaminated by Volatile Chemical Substances

This work developed a model for predicting the volatilization flux from the unsaturated soil contaminated by volatile chemical substances (VCSs) such as mercury and benzene. The model considers a series of phenomena under the unsaturated condition such as multi-phase flow consisting of a non-aqueous phase liquid, water, and gases together with the permeation of rainfall into the surface soil, the volatilization/condensation of VCSs, and the adsorption/desorption of VCSs. On this basis, this work clarified a mechanism for the generation of a volatilization flux at the ground surface. In addition, the effects of various transport phenomena in the surface soil on the magnitude and seasonal changes in this flux due to variations in weather factors such as rainfall level, temperature, and air pressure were quantitatively evaluated. This newly developed prediction model can be utilized to estimate dynamic variations in the flux under real-environmental conditions.

Development of a numerical model for predicting the volatilization flux from unsaturated soil

<p>In recent years, exposure to volatile chemical substances (VCSs) from contaminated soil has become a serious problem so it has become increasingly important to study the transport phenomena of VCSs. In this study we focused on the transport phenomena of VCSs at the boundary layer between the soil surface and the atmosphere, and defined it as volatilization flux, which express the amount of volatilized substances per unit volume per unit time. In order to estimate the phenomena of mercury transport in unsaturated soil and mercury released from soil to the atmosphere, it is necessary to consider in detail the spatiotemporal fluctuations of factors that affect the volatilization of mercury and the physical transport phenomena in soil.</p><p>The present study developed a model for predicting the volatilization flux from the unsaturated soil contaminated by VCSs. The model considers a series of phenomena under the unsaturated condition such as gas-liquid two-phase flow consisting of convection and diffusion. The effects of various transport phenomena on the surface soil on changes in the magnitude of this flux due to variations in meteorological factors such as temperature and soil moisture content were quantitatively evaluated. This developed prediction model can be utilized to estimate dynamic variations in the flux under real-environmental conditions.</p>

Transient unsaturated shaft resistance of a single pile during water flow

The pile foundations’ design is commonly based on the soil’s initial in situ condition during field investigations or the assumption of its saturated condition. However, for some regions in tropical weather, a significant part of the pile shaft remains above the groundwater table (i.e., unsaturated condition) during the structure’s lifespan. Only considering a constant moisture condition in the soil (unsaturated or saturated) can overestimate or underestimate the pile design. The soil shear strength governs the shaft resistance of a pile and depends on the soil matric suction, which is significant in the unsaturated zone. In this study, an analytical model is proposed to estimate piles’ unsaturated shaft resistance and encourage the use of unsaturated soil mechanics in engineering practice. The mathematical equation involves well-known parameters from unsaturated soil mechanics theory and simulates the pile shaft resistance variation with its length and time, considering a unidimensional infiltration downwards (e.g., during a rainfall event).

Swelling pressure of a sodium bentonite in solutions of different suction

In this study, the swelling pressure of unsaturated, compacted bentonite-sand mixture was measured, which the all samples had experiment in dying-wetting history in suction changing. This test program used Kunigel V1 as sodium type. Constant volume swelling test was conducted out that swelling pressure was measured using a developed apparatus. A pressure sensor was mounted in the swelling test apparatus. Previously, the all samples deformed due to suction change (i.e. drying-wetting process in suction). Two types were prepared before applying suction that were initial unsaturated condition and saturated condition on same initial dry density. Swelling pressure and adsorbed water amount was monitored in the test, which lasted for one month.

The Initial Deposition Behavior of Silica Colloid and Amino-Modified Silica Colloid in Unsaturated Sand Columns

Colloid transport experiments focusing on the initial deposition stage in water-unsaturated sand columns were conducted. To examine the effect of electrostatic interaction in the unsaturated condition, negatively and positively charged silica colloids were used for column transport experiments under different salt concentrations. The results of the column experiments were analyzed based on the colloid filtration theory and the deposition rate constants, and the single collector efficiency was calculated. The deposition rate constants of both negatively and positively charged silica in a water-unsaturated condition are larger than those in a water-saturated condition at an equivalent salt concentration, because the interface between air and water acts as an additional deposition site. The negatively charged silica shows the salt concentration, above which electric double layer (EDL) repulsion can be neglected, and the salt concentration is called critical deposition concentration (CDC). The CDCs were almost the same values in water-saturated as well as unsaturated conditions. The deposition rate constants of the positively charged silica were slightly increased at 0.05 mM due to the EDL attractive forces in the saturated condition. However, we could not see the significant effects of the EDL attractive force in the unsaturated condition in this study. Also, the present results demonstrated that a correlation equation for calculating collector efficiency can be applied to the non-spherical collector particles.

Improvement of Bearing Capacity of Clay Soil Using Fly Ash

The principal aim of the study is to improve the engineering properties of the soil sample using fly ash as a binding material. Bangladeshi fly ash was used in this study. Effects of fly ash on physical and mechanical properties of soil (Atterberg limits, moisture-density relationship, and unconfined compressive strength) are evaluated in the presence of 0%, 2%, 4%, 5%, 8%, 10%, 15%, 20% & 25% fly ash. For understanding the improvement of engineering properties of soil, a parametric analysis is conducted to determine the allowable bearing capacity, settlement and the time required for the consolidation. The allowable bearing capacity is evaluated using several equations for both saturated and unsaturated conditions. It is found that for 5% fly ash content, the maximum allowable bearing capacity is achieved. The maximum value of allowable bearing capacity is 660.12 kN/m2 in the unsaturated condition. The increment of maximum allowable bearing capacity is 77.74% for 5% fly ash content. The lowest value of the settlement was 336 mm (saturated) and 183 mm (unsaturated) for 25% fly ash content. Considering normally consolidated soil, it is found that the least time required for consolidation is 3.19 years for 25% fly ash content.

Adaptive Fringe Projection for 3D Shape Measurement with Large Reflectivity Variations by Using Image Fusion and Predicted Search

There is always a great challenge for the structured light technique that it is difficult to deal with the surface with large reflectivity variations or specular reflection. This paper proposes a flexible and adaptive digital fringe projection method based on image fusion and interpolated prediction search algorithm. The multiple mask images are fused to obtain the required saturation threshold, and the interpolated prediction search algorithm is used to calculate the optimal projection gray-level intensity. Then, the projection intensity is reduced to achieve coordinate matching in the unsaturated condition, and the adaptive digital fringes with the optimal projection intensity are subsequently projected for phase calculation by using the heterodyne multifrequency phase-shifted method. The experiments demonstrate that the proposed method is effective for measuring the high-reflective surface and unwrapping the phase in the local overexposure region completely. Compared with the traditional structured light measurement methods, our method can decrease the number of projected and captured images with higher modulation and better contrast. In addition, the measurement process only needs two prior steps and avoids hardware complexity, which is more convenient to apply to the industry.

Modeling Back-of-Queue Uncertainty at Signalized Intersections

The queue percentile formulation adopted in the 2010 Highway Capacity Manual (HCM) is empirically based. It contains an overly simplified functional form and parameters such that the accuracy of the back-of-queue percentile estimates is compromised. In view of this, the author applies the Delta method to derive the uncertainty formulation of back-of-queue through the first-order Taylor expansion approximation, assuming that the source of uncertainty comes from arrival flow, saturation flow and, for actuated controller, green time variability from vehicle actuation. As multiplication of the independent, positive random variables results in a lognormal distributed outcome, the back-of-queue percentile is quantified as a lognormal predictive interval function. The simulation study shows that the proposed back-of-queue predictive interval is much more accurate than the HCM counterpart in most of the cases evaluated based on the Kolmogorov–Smirnov goodness-of-fit test. The proposed formulations can be used to quantify the back-of-queue predictive interval for both pre-timed and actuated control, whereas HCM is indifferent to the type of control. As expected, the variability of back-of-queue from the actuated control is less than the pre-timed control in unsaturated condition. The predictive interval profiles become identical when the degree of saturation approaches to unity and maxes out the green time.

Fundamental Study on Transport Model for Radionuclides under Unsaturated Condition around Near-Surface Underground

ABSTRACTThe low-level nuclear wastes such as decontamination waste from Fukushima are disposed in near-surface underground, where the intermittent recharge of rain and groundwater causes spatial distribution of water content. Therefore, pores of soils are not filled with water, that is, an unsaturated zone will be formed. In such a condition, since the water flow path are detoured by clogged gas in pores of soil in the unsaturated zone, the migration path of radionuclide would be different from the saturated zone. So far, the one-dimensional advection-dispersion equation (ADE) model has been widely used in order to explain experimental results under an unsaturated condition. However, the detouring of local flow-paths remarkably affects the mass transfer. The one-dimensional ADE evaluates such a detouring effect by using Peclet number and retardation coefficient as fitting parameters. In other words, the one-dimensional ADE model is difficult to explain mass transfer under an unsaturated condition. Therefore, the purpose of this study is explaining such complicated transport of radionuclides using a multi-path model based on phenomena in underground. The proposed multi-path model considering both water saturation and permeability distributions showed good agreement with the experimental data under an unsaturated condition.