The feasibility and efficiency of transporting lead under electric fields are investigated at pilot scale in three 1 t Georgia kaolinite specimens spiked with lead nitrate solution and at an electrode spacing of 72 cm. Enhancement methods such as cathode depolarization and/or catholyte neutralization techniques are not used in processing. A constant direct current density of 133 μmA/cm ² is applied. Two of the tests are conducted on specimens spiked with lead at concentrations of 856 mg/kg and 1,533 mg/kg. The third test is conducted on a 1:1 mixture of compacted kaolinite/sand spiked with lead at a concentration of 5,322 mg/kg. Lead was transported toward the cathode and precipitated at its hydroxide solubility value within the basic zone in direct contact with the cathode compartment. Subsequent to 2,950 h of processing and an energy expenditure of 700 kWh/m ³, 55% of the lead removed across the soil was found precipitated within the last 2 cm close to the cathode, 15% was left in the soil before reaching this zone, 20% was found precipitated on the fabric separating the soil from the cathode compartment, and 10% was unaccounted. Heavy metals and species that are solubilized in the anodic acid front can be efficiently transported by electromigration under an electrical field applied across electrodes placed in soils.

A mathematical model is presented for multicomponent species transport under coupled hydraulic, electric, and chemical potential differences. Mass balance of species and pore fluid together with charge balance across the medium result in a set of differential equations. Sorption, aqueous phase, and precipitation reactions are accounted by a set of algebraic equations. Instantaneous chemical equilibrium conditions are assumed. Transport of H ⁺ , OH ⁻ , Pb ²⁺ , $\mathrm{NO}{}^{\mathit{-}}\text{,}$ the associated chemical reactions, electric potential, and pore pressure distribution across the electrodes in electrokinetic remediation are modeled. Model predictions of acid transport, lead transport, and pore pressure distribution display very good agreement with the pilot-scale test results validating the formalisms offered for multicomponent transport of reactive species under an electric field. The model also bridges the gap between the electrochemistry and mechanics in electroosmotic consolidation of soils.

This paper describes torsional ring shear tests on interfaces comprised of high-density polyethylene (HDPE) geomembranes/nonwoven geotextiles and a drainage geocomposite. Four textured geomembranes with three different manufacturing techniques are utilized to investigate the effect of geomembrane texturing on interface shear resistance. In addition, the effects of geotextile fiber type, fabric style, polymer composition, calendering, and mass per unit area on textured HDPE geomembrane interface strengths are investigated. The textured HDPE geomembrane/nonwoven geotextile and drainage geocomposite interfaces exhibited a large postpeak strength loss. This strength loss is attributed to pulling out or tearing of filaments from the nonwoven geotextile and orienting them parallel to shear, and polishing of the texturing on the geomembrane. At high normal stresses, the strength loss can be caused by damage to or removal of the texturing on the geomembrane surface.

Large-scale tests were performed to determine the effect of a cycle of wetting and drying on the hydraulic conductivity of several geosynthetic clay liners (GCLs). The GCLs were covered with 0.6 m of pea gravel and permeated with water. After steady seepage had developed, the water was drained away, and the GCL was desiccated by circulating heated air through the overlying gravel. The drying caused severe cracking in the bentonite component of the GCLs. The GCLs were again permeated with water. As the cracked bentonite hydrated and swelled, the hydraulic conductivity slowly decreased from an initially high value. The long-term, steady value of hydraulic conductivity after the wetting and drying cycle was found to be essentially the same as the value for the undesiccated GCL. It is concluded that GCLs possess the ability to self-heal after a cycle of wetting and drying, which is important for applications in which there may be alternate wetting and drying of a hydraulic barrier (e.g. within a landfill final cover).

Agarose, a derivative of the natural polymer, agar, is proposed as an impregnate to stabilize the in-situ structure of cohesionless soils before sampling. The gel solution is injected into the in-situ voids after heating the soil. Sampling is performed using conventional sampling techniques and gel removal is achieved in the laboratory test device by reheating the specimen and flushing out the agarose with warm water. The process of heating, impregnation with agarose, cooling, reheating, and agarose removal was found to have no significant effect on the cyclic mobility of two contractive Ottawa sands. The technology shows promise for an accurate estimate of the in-situ void ratio and for an economic undisturbed sampling of cohesionless soils.

With a limited amount of data on soil properties and limited instrumentation readings, important aspects of lock performance from initial construction through major flood events, including siltation, were reasonably estimated using the backfill placement method of analysis. Results of the complete soil-structure-foundation interaction analyses for four operational load cases were essential to interpreting instrumentation measurements. Soil-structure interaction between the compacted sand backfill and the stem walls was distinguished from the interaction between the compacted sand backfill and the culvert walls. This study allowed for the characterization of the range in magnitudes and distributions (with elevation) of horizontal earth pressure coefficient, K _h , and vertical earth pressure coefficient, K_v , along the stem and culvert walls for each load case. Distributions of K_v with elevation have not been published to date. Expressing the effective normal pressure and vertical shear stress along lock walls in terms of the earth pressure coefficients, K _h and K_v , allowed for the precise recovery of both normal and shear stresses (computed using sophisticated analytical procedures) for use in simplified design tools.

Short fibers have been tried in the past few years as a soil-improvement admixture (reinforcement), yet no failure criteria for fiber-reinforced soils, consistent with numerical methods for solving boundary-value problems, are available. An attempt at deriving the limit condition for a fiber-reinforced granular soil is presented. An energy-based homogenization scheme is used to arrive at the macroscopic failure stress of the fibrous granular composite. A piecewise closed-form failure criterion is derived. The internal friction angle is used to quantify the strength of the granular matrix, and the fibers are characterized by volumetric concentration, aspect ratio, yield point, and the fiber-soil interface friction angle. Laboratory tests on specimens with low fiber content indicate a good agreement of the model predictions with the actual test results.

In an earlier paper, the writer presented a simple stochastic model of the grain and pore structure in cohesionless soils and similar materials. Equations that very adequately predict the void ratio as a function of grain-size distribution were derived. In this technical note, the stochastic model is used to find the distribution of void volume as a function of void size (void-chord length). An evaluation of laboratory tests shows that both the bubbling pressure of a soil and the size of the largest grain that can pass through the voids of a soil in a base-filter compatibility test can be correlated with the calculated mean void chord of the soil.