Hydraulic Conductivity Testing and Destructive Sampling of Field-Scale Mine Waste Test Piles

A commingled waste rock and tailings test pile and a waste rock test pile were evaluated to determine saturated hydraulic conductivity and destructively sampled to measure dry density. The commingled test pile contained a mixture of filtered tailings and waste rock blended to isolate waste rock particles as inclusions within the tailings matrix. Test piles were constructed in the shape of truncated 5-m tall pyramids with 25-m base sides and flat 5-m × 5-m top surfaces, and instrumented to monitor water content (and additional geochemical indicator parameters) within the test pile and seepage from the base of the pile. Piles were decommissioned after 26 months of operation. Saturated hydraulic conductivities were measured using sealed double ring infiltrometers (2.4-m square outer-ring and 1-m square inner-ring). Tensiometers and embedded water content sensors were used to measure progression of the wetting front, and the final location of the wetting front in the commingled test pile was directly measured during decommissioning. Field-measured saturated hydraulic conductivities were compared to laboratory-measured results intended to simulate the test piles. Despite having a lower average density, the commingled waste rock and tailings had a hydraulic conductivity approximately 2.5-times lower than the waste rock.

Numerical Modelling of Liquid Film Spreading Dynamics over Smooth Vertical Surface under Isothermal Conditions

The paper presents numerical modelling of the liquid film spreading dynamics of the R21 (mol. fraction: 0.9) and R114 refrigerants mixture. We considered an outer flow along a round vertical cylinder at Reynolds number of 104 and various contact angles. The simulation was performed in OpenFOAM software on the basis of the volume of fluid (VOF) method. We have shown that the wetting front deforms at wetting angles of 30 and 50 degrees, and regular jets form. At the same time, it was demonstrated that at the wetting angle of 10 degrees the spreading front has practically a flat shape, but one may see some regular thickenings of the liquid film along the contact line of the front.

Hydraulic characteristics of plow pan constructed sandy paddy soil by adding fly ash

The feasibility of mixing fly ash to sandy soil to build the artificial plow pan of paddy soil in the Yellow River beach was explored. Water infiltration characteristics, saturated hydraulic conductivity, saturated water content and water storage capacity of the artificial plow pan were measured by using laboratory column tests. The results showed that under the same bulk density, when the amount of fly ash increased, the movement rate of the plow pan wetting front, the infiltration rate and the saturated hydraulic conductivity were decreased, then the water content and water storage of the soil layer increased. When the application amount of the fly ash was the same, and when the compaction weight decreased, the wetting front movement rate and saturated hydraulic conductivity increased and the soil water content and water storage capacity decreased. Mixing of fly ash with sand at a ratio of 1:3 (by weight) was found to be ideal for making an artificial of plow pan having bulk density of 1.7 g/cm3. Bangladesh J. Bot. 50(3): 993-1002, 2021 (September) Special

Experimental evaluation of salinity geosynthetics capillary barriers

This paper explores the transient upward flow of saline water in one-dimensional soil and soil-geosynthetics columns to evaluate preventive measures to mitigate salinity rise. Unsaturated soil concepts are utilised to elucidate the salinity movement through geotextile and geocomposite drain interfaces. The presence of a geotextile layer slowed down the capillary rise of the saline water. However, it did not prevent the breakthrough of the saline water due to the hydrophilicity of the geotextile and the suction at the geotextile base being close to the geotextile's water entry suction value. In contrast, using a geocomposite drain mitigated the upward saline wetting front. It acted as a salinity capillary barrier due to the initial hydrophobicity of its geotextile component and the air gap present in the geonet core.

Simulation of the Infiltration of Fractured Rock in the Unsaturated Zone

We study infiltration of rainwater into fractured rock and the accompanying capillary exchange processes between fractures and matrix, hereafter referred to as fracture–matrix transfer (FMT). Its influence on the velocity of the wetting front for uniform and variable aperture fractures is of prime interest because it determines the penetration depth of infiltration pulses. FMT is modelled explicitly in a discrete fracture and matrix (DFM) framework realised using a hybrid finite element–finite volume discretisation with internal boundaries. The latter separate the fracture mesh from the rock matrix mesh with the benefit that the flow that occurs within the minute fracture subvolume can be tracked with great accuracy. A local interface solver deals with the transient nonlinear aspects of FMT, including spontaneous imbibition of the rock matrix. Two- and three-dimensional heuristic test cases are used to illustrate how FMT affects infiltration. For the investigated scenario, we find that—beyond a critical fracture aperture around 5–10-mm—infiltration rate is no longer affected by FMT. Fracture aperture variations promote in-fracture-plane fingering, with counter-current flow of water (downward) and air (upward). Fracture flow interacts with FMT in a complex fashion. For systems with a small fracture porosity (≤0.01%), our results suggest that intense, hour-long rainfall events can give rise to tens-of-meter-deep infiltration, depending on fracture/matrix properties and initial saturation of the fractured rock mass.

Flow Effects on the Transient Behavior of Vapor Film and Bubbles During Forced-Convective Quenching Experiments

The transient behavior of boiling phenomena during quenching of an AISI 304 stainless steel, conical-end, cylindrical probe in flowing water at 60 °C was studied. Two free-stream velocities (0.2 and 0.6 m/s) and two initial probe temperatures (850 and 950 °C) were investigated. From high-speed video recordings, undulations of the liquid vapor interface that appear periodically and propagate in the direction of the flow stream were observed during the vapor film stage. After the collapse of the vapor film, a wetting front is formed which consists of many small bubbles that coalesce rapidly in a small area while fewer and larger bubbles nucleate and grow below it. The initial temperature has a marginal effect on the size and half-life of the large bubbles. However, the water flow rate produces larger values of maximum diameter and half-life time for water flowing at 0.2 m/s than their equivalents for 0.6 m/s.

It rains and then? Numerical challenges with the 1D Richards equation in kilometer-resolution land surface modelling

Over the last decade kilometer-scale weather predictions and climate projections have become established. Thereby both the representation of atmospheric processes, as well as land-surface processes need adaptions to the higher-resolution. Soil moisture is a critical variable for determining the exchange of water and energy between the atmosphere and the land surface on hourly to seasonal time scales, and a poor representation of soil processes will eventually feed back on the simulation quality of the atmosphere. Especially the partitioning between infiltration and surface runoff will feed back on the hydrological cycle. Several aspects of the coupled system are affected by a shift to kilometer-scale, convection-permitting models. First of all, the precipitation-intensity distribution changes to more intense events. Second, the time-step of the numerical integration becomes smaller. The aim of this study is to investigate the numerical convergence of the one-dimensional Richards Equation with respect to the soil hydraulic model, vertical layer thickness and time-step during the infiltration process. Both regular and non-regular (unequally spaced) grids typical in land surface modelling are considered, using a conventional semi-implicit vertical discretization. For regular grids, results from a highly idealized experiment on the infiltration process show poor numerical convergence for layer thicknesses larger than approximately 5 cm and for time steps greater than 40 s, irrespective of the soil hydraulic model. The velocity of the wetting front decreases systematically with increasing time step and decreasing vertical resolution. For non-regular grids, a new discretization based on a coordinate transform is introduced. In contrast to simpler vertical discretizations, it is able to represent the solution second-order accurate. The results for non-regular grids are qualitatively similar, as a fast increase in layer thickness with depth is equivalent to a lower vertical resolution. It is argued that the sharp gradients in soil moisture around the propagating wetting front must be resolved properly in order to achieve an acceptable numerical convergence of the Richards Equation. Furthermore, it is shown that the observed poor numerical convergence translates directly into a poor convergence of infiltration-runoff partitioning for precipitation time series characteristic of weather and climate models. As a consequence, soil simulations with low resolution in space and time may produce almost twice the amount of surface runoff within 24 hours than their high-resolution counterparts. Our analysis indicates that the problem is particularly pronounced for kilometer-resolution models.