Assessment of The Dioxins Leaching Potentials In Selected Soils Through Breakthrough Curves (BTCs) Model

The current study was to investigate the leaching and groundwater contamination potential of selected Dioxins, in local soil series. Solute transport was modelled through Breakthrough curve (BTC) plots, based on distribution coefficient (Kd), Retardation factor and Dispersivity, under normal velocity (20 cm day -1) and preferential or steady flow (50 cm day -1). In case of Dibenzo -p- Dioxin (DD), distribution coefficient values were found in order of Charsadda > Peshawar > Sultanpur series, while for 2 Chloro- p- Dioxin (2Cl-DD), the order was Charsadda > Sultanpur > Peshawar. However, the overall sorption was low. Under the normal velocity both of selected Dioxins (DD & 2Cl-DD), BTC plots relatively took longer time to reach the point of saturation as compared to high seepage velocity. However, the overall solute transport was found to be rapid. This behaviour showed that sorption of the Dioxins selected soil series is low and there is potential for leaching and groundwater contamination.

Seepage and Dynamic Characteristics of Carbonaceous Mudstone Coarse-Grained Soil Embankment with Different Gradations

This study investigates the seepage and deformation characteristics of carbonaceous mudstone coarse-grained soil embankment with different gradations under the action of dynamic load and rainfall. An indoor geotechnical test is conducted, and the mechanical parameters of carbonaceous mudstone coarse-grained soil with different gradations are analyzed. A numerical calculation model of seepage and dynamic characteristics of carbonaceous mudstone coarse-grained soil embankment is established on the basis of the test data. The different effects of rainfall infiltration and vehicle load are evaluated. The seepage, settlement, and slope stability evolution characteristics of graded carbonaceous mudstone coarse-grained soil embankment slope are studied. Results show that under the condition of the same rainfall time, the greater the nonuniformity coefficient, the faster the decrease in pore water pressure of the coarse-grained soil embankment at the same monitoring point. The seepage velocity vector in the embankment is concentrated below the soil shoulder. The smaller the saturated permeability coefficient and saturated water content, the larger the seepage velocity vector. The greater the nonuniformity coefficient, the larger the coarse-grained soil embankment under vehicle load. The smaller the embankment settlement, the lower the safety factor of embankment. The safety factor decreases slowly at first and then decreases rapidly in the whole study period under the effect of dynamic wetting. The research results provide a theoretical reference for the practical engineering application of carbonaceous mudstone coarse-grained soil embankment in rainy areas.

ANTI-EROSION CAPACITY OF A GRANULAR FILTER SUBJECTED TO A PERIODICALLY VARIABLE HYDRAULIC GRADIENT

The instability of a filter system is a significant cause of seepage failure in embankment projects. The filter system in the earth-rock embankment is mainly composed of graded cohesionless soil. To uncover the performance of the granular filter in resisting the internal erosion, a set of experiments was carried out with an improved experimental apparatus, considering different hydraulic loading scenarios. The movement of graded cohesionless soil, the seepage velocity and the hydraulic gradient were monitored in the experiments. It was found that during the process of increasing the hydraulic gradient, the failure of the granular filter mainly experienced three stages: the first one was the dynamic equilibrium stage; the second was the critical start stage; and the third was the failure stage, in which a sudden change in the seepage velocity was the precursor of seepage failure. The critical hydraulic gradient and destructive hydraulic gradient decreased with the water level amplitude. Moreover, the experiments revealed that the loading modes of the hydraulic gradient significantly influenced the anti-erosion capacity of the granular filter. Compared with the stepwise loading mode, the cyclic reciprocating loading mode greatly weakened the anti-erosion capacity of the granular filter under the same water level amplitude. The destructive hydraulic gradient of the latter was only 71.8 % of the former under a higher water level amplitude, indicating that the corresponding measures should be considered to avoid the occurrence of a periodically variable hydraulic gradient.

Thermal Oscillations in Sea Ice and Soils

<p><b>We present mathematical analysis of temperature oscillations in depth-dependent media by investigating the thermodynamics of sea ice and of soils. Time-series temperature measurements from thermistor strings are common in both sea ice and soils and are used to study their properties, evolution, seepage flux and a host of interactions with their environment. We use numerical tools and perturbation theory to study the propagation of high frequency, small amplitude temperature oscillations through the in-homogeneous media using one dimensional models. Analytical tools for studying such thermal waves are derived.</b></p> <p>In sea ice the absorption of solar radiation and oscillating air temperatures result in two distinct thermal wave propagation behaviours. At depths, stationary waves associated with in place solar heating are observed, whereas near the surface, travelling thermal waves are present due to the quick decay in the absorbed solar radiation and the oscillatory air temperatures. These are observed in thermistor string data taken in McMurdo Sound, Antarctica between 1996-2003. Using a variety of mathematical tools, the leading order behaviour of the diurnal temperature oscillation is approximated in terms of elementary functions and is compared with results from numerical simulations.</p> <p>The thermodynamics of soils differ from sea ice in that all the solar radiation is absorbed at the upper boundary and water movement within the soil carries heat. Macroscale in-homogeneity in the advection-diffusion equation is considered and the thermal wave propagation characteristics are studied using a WKB approximation. The leading order behaviour is shown to reduce exactly to the Stallman equations, being the solution to the thermal wave propagation in a homogeneous soil with constant, uniform water flow. We use the leading order WKB expansion to estimate errors in the homogeneous soil assumption commonly made to estimate the seepage velocity and soil diffusivity. It is shown that the diffusivity estimations are relatively stable and provide reasonably accurate results, but the seepage velocity estimations incur significant errors that should be considered. A frequency dependence in the error leads us to suggest multi-frequency analysis for detection and further studies of the effects of in-homogeneous soil thermodynamics.</p>

Thermal Oscillations in Sea Ice and Soils

<p><b>We present mathematical analysis of temperature oscillations in depth-dependent media by investigating the thermodynamics of sea ice and of soils. Time-series temperature measurements from thermistor strings are common in both sea ice and soils and are used to study their properties, evolution, seepage flux and a host of interactions with their environment. We use numerical tools and perturbation theory to study the propagation of high frequency, small amplitude temperature oscillations through the in-homogeneous media using one dimensional models. Analytical tools for studying such thermal waves are derived.</b></p> <p>In sea ice the absorption of solar radiation and oscillating air temperatures result in two distinct thermal wave propagation behaviours. At depths, stationary waves associated with in place solar heating are observed, whereas near the surface, travelling thermal waves are present due to the quick decay in the absorbed solar radiation and the oscillatory air temperatures. These are observed in thermistor string data taken in McMurdo Sound, Antarctica between 1996-2003. Using a variety of mathematical tools, the leading order behaviour of the diurnal temperature oscillation is approximated in terms of elementary functions and is compared with results from numerical simulations.</p> <p>The thermodynamics of soils differ from sea ice in that all the solar radiation is absorbed at the upper boundary and water movement within the soil carries heat. Macroscale in-homogeneity in the advection-diffusion equation is considered and the thermal wave propagation characteristics are studied using a WKB approximation. The leading order behaviour is shown to reduce exactly to the Stallman equations, being the solution to the thermal wave propagation in a homogeneous soil with constant, uniform water flow. We use the leading order WKB expansion to estimate errors in the homogeneous soil assumption commonly made to estimate the seepage velocity and soil diffusivity. It is shown that the diffusivity estimations are relatively stable and provide reasonably accurate results, but the seepage velocity estimations incur significant errors that should be considered. A frequency dependence in the error leads us to suggest multi-frequency analysis for detection and further studies of the effects of in-homogeneous soil thermodynamics.</p>

A Unified View of Nonlinear Resistance Formulas for Seepage Flow in Coarse Granular Media

There are many studies on the nonlinear relationship between seepage velocity and hydraulic gradient in coarse granular materials, using different approaches and variables to define the resistance formula applicable to that type of granular media. On the basis of an analysis of the existing formulations developed in different studies, we propose an approach for comparing the results obtained by some of the most important studies on state-of-the-art seepage flow in coarse granular media.

Experimental Study on the Lateral Seepage Characteristics in the Tension Saturated Zone

To study the lateral seepage field in the tension saturated zone (TSZ), an experiment with no evaporation and precipitation infiltration was carried out in a self-made seepage tank filled up with fine sand. Based on the data and plots obtained, the lateral seepage field distribution features in the TSZ can be divided into three area for discussion: ascending area, descending area, and the nearly horizontal flow area. In the ascending and descending area, the total water potential gradient diminished from the recharge area to the discharge area and the seepage velocity was faster. In the nearly horizontal flow area, the total water potential gradient was lower and the seepage velocity was slower. The pressure potential gradually decreased horizontally from the recharge area to the discharge area, while in the vertical profile, it gradually decreased from the bottom to the top in the whole seepage area. In the absence of evaporation, the vertical water exchange among the saturated zone, TSZ, and unsaturated zone in nearly horizontal flow area is weak. Contrarily, in the ascending area and descending area, vertical water flows through both the phreatic surface and the upper interface of the TSZ. When there is lateral seepage in the TSZ, the thickness of the TSZ generally increases from the ascending area to the nearly horizontal area and then to the descending area. It should be pointed out that in the nearly horizontal area, the TSZ thickness is approximately equal to the height of the water column. Overall, the lateral seepage in the TSZ can be regarded as a stable siphon process, hence the siphon tube model can be further used to depict this lateral seepage.

Analytical expressions for macrodispersion in three-dimensional Sub-Gaussian hydraulic conductivity fields

&lt;p&gt;Subsurface flow and transport settings are typically characterized by spatial variability of the underlying hydro-geological attributes (e.g., permeability and porosity) and a high degree of uncertainty associated with data and model parameter estimates. In this context, we rely on a stochastic approach and analyse conservative solute transport taking place within three-dimensional, sub-Gaussian domains with isotropic, exponential correlation structure of the associated log-conductivity fields. The flow is uniform in the mean and driven by an imposed average head gradient. We present an analytical solution based on a small perturbation approach that allows assessing the temporal evolution of longitudinal and transverse macrodispersion. Similar to what is observed for Gaussian log-conductivity domains, these are seen to attain a (&lt;em&gt;Fickian&lt;/em&gt;) asymptotic regime after the solute plume has travelled a sufficient number of conductivity correlation scales. We also derive closed-form analytical expressions for other statistical moments of interest (e.g., seepage velocity and particle displacement covariance) and benchmark these solutions against numerical Monte Carlo simulations for various degrees of domain heterogeneity. This enables us to assess the extent at which a small perturbation approximation can embed the key features of macrodispersion within three-dimensional sub-Gaussian conductivity fields of increasing heterogeneity levels. Our results suggest that, similar to what already observed for Gaussian fields, the analytical formulation fully captures the trend of longitudinal macrodispersion for values of log-conductivity variance smaller than the unity, the goodness of the results becoming worse as the variance increases. Our formulation also captures directional displacement and seepage velocity covariances, even though the degree of agreement with their numerical Monte Carlo counterparts rapidly deteriorates with increasing conductivity variance. Particularly refined numerical grids are required to capture the nugget effect exhibited by the analytical longitudinal velocity covariance, thus posing a challenge to assess the system behaviour at short distances.&lt;/p&gt;

Finite element analysis on permeability of cut-off wall for landfill

<p><span>Finite element method is an efficient numerical calculation method based on information technology, which can be used to solve complex equations in various problems. At present, the finite element method is mainly used to deal with seepage problems in dams, while there is less study on seepage in landfill. In this paper, finite element method is used to analyze the seepage of cut-off wall of a landfill in Jiangsu Province, and the movement of landfill leachate in cut-off wall under different conditions is simulated. The simulation results show that The cut-off wall can effectively slow down the seepage velocity of leachate; Under different conditions, the maximum gradient of the cut-off wall are 18.68 and 13.84 respectively, which conforms to Chinese national standard. Therefore, the design of cut-off wall is safe and reasonable, and filtration erosion will not occur; This simulation method combined with information technology can provide new solutions and ideas for other projects to verify safety and rationality.</span></p>