Jangguen Lee

Investigation of Consolidation-Induced Solute Transport. II: Experimental and Numerical Results

This paper presents an experimental and numerical investigation of consolidation-induced solute transport. Diffusion and large strain consolidation tests were performed on composite specimens of kaolinite clay consisting of an upper uncontaminated layer and a lower layer contaminated with potassium bromide. Experimental measurements of effluent concentration, solute mass outflow, and final concentration profiles were obtained for a variety of initial, boundary, and loading conditions, including unload/reload. Numerical simulations were conducted using a computational model in which solute transport occurs by advection, dispersion, and sorption and is consistent with temporal and spatial variations of porosity and seepage velocity in the consolidating layer. Large strains were taken into account as well as variation of effective diffusion coefficient with porosity and nonlinear nonequilibrium sorption effects. The numerical simulations are in good to excellent agreement with the experimental measurements. Results indicate that, depending on conditions, diffusion and consolidation-induced advection can make important contributions to solute transport and mass outflow. Thus, both mechanisms should be considered for transport analyses involving soft contaminated clays undergoing large volume change. Results also indicate that nonequilibrium sorption effects were not significant for the materials and test conditions used in this study.

Evaluation of a dry FGD material as a flowable fill

Abstract Many flue gas desulfurization (FGD) materials have low unit weight and good shear strength characteristics and thus hold promise for flowable fill applications. This paper focuses on the potential of using spray dryer FGD ash in flowable fill as a replacement for conventional fly ash. Several design mixes were considered. The design mixes consisted of varying amounts of FGD, cement, lime, admixture, and water. The mixes were tested in the laboratory for flowability, unit weight, moisture content, unconfined compressive strength (UCS), erodibility, set time, penetration, and long-term strength characteristics. Tests were conducted for up to 90 days of curing. The FGD flowable fill without any additives was observed to be comparable to regular (normal set) flowable fill in terms of placeability, UCS, and ‘diggability’. FGD flowable fill with additives and admixtures compared favorably with the characteristics of conventional quick-set flowable fills.

Investigation of Consolidation-Induced Solute Transport. I: Effect of Consolidation on Transport Parameters

This paper presents an experimental investigation of the effect of clay consolidation on parameters that govern the advective-dispersive transport of an inorganic solute. Batch, diffusion, dispersion, and solute transport tests were conducted using kaolinite clay and dilute solutions of potassium bromide (KBr). Batch tests produced the highest levels of K+ sorption and indicated that equilibrium sorption was achieved in approximately 10–30 min. The increase in sorption observed in the batch tests, as compared to the dispersion or solute transport tests, reflects the significantly lower solids-to-solution ratio and more efficient mixing process. By comparison, kaolinite consolidation had little effect on sorption due to the relatively small change in porosity. Values of hydrodynamic dispersion coefficient ( Dh ) , effective diffusion coefficient ( D∗ ) , and apparent tortuosity factor decreased with decreasing porosity. Values of D∗ obtained for Br− were generally larger than for K+ , whereas Dh values for...

Coupled Consolidation and Contaminant Transport in Compressible Porous Media

This paper presents an experimental and numerical investigation of coupled consolidation and contaminant transport in compressible porous media. Numerical simulations were performed using the CST2 computational model, in which a dual-Lagrangian framework is used to separately follow the motions of fluid and solid phases during consolidation. Diffusion and large strain consolidation-induced transport tests were conducted on composite specimens of kaolinite slurry consisting of an upper uncontaminated layer and a lower layer contaminated with potassium bromide. Assessment of the importance of the consolidation process on solute transport is based on measured and simulated solute breakthrough curves and final contaminant concentration profiles. CST2 simulations closely match the experimental data for three different loading conditions. Diffusion and consolidation-induced advection made important contributions to solute transport and mass outflow in this study. Additional simulations indicate that consolidati...

Efficiency of Seepage Consolidation for Preparation of Clay Substrate for Centrifuge Testing

Seepage consolidation under normal gravity conditions can be used to prepare clay soil substrates for subsequent testing in a geotechnical centrifuge. Currently available information provides no information regarding the general efficiency of this method, which would be expected to vary widely depending on centrifuge, test specimen, and operating conditions. A numerical investigation is presented of the efficiency of the two-stage seepage/centrifuge consolidation method for the preparation of normally consolidated clay substrates. Large strain consolidation simulations and experimental data for centrifuge and seepage/centrifuge consolidation tests conducted on reconstituted Singapore marine clay are in excellent agreement. A parametric study illustrates the effects of initial specimen void ratio, initial specimen height, surcharge stress, swelling time, and acceleration factor on the efficiency of the two-stage substrate preparation method. Efficiency of the method for Singapore marine clay ranged from 55 to essentially 100% for the simulations conducted.

Flowable Fill Using Flue Gas Desulfurization Material

Flowable fills are an effective and practical alternative to commonly used compacted earth backfills. Flowable fill is a cementious material, commonly a blend of cement, fly ash, sand, and water, that does not require compaction, may be self-leveling at time of placement, may harden quickly within a few hours, and can be excavated in the future if need be. Many flue gas desulfurization (FGD) materials have low unit weight and good shear strength characteristics and thus hold promise for flowable fill applications. This paper focuses on the potential of using two types of FGD materials (spray dryer and wet fixated FGD material) in flowable fill as a replacement for conventional fly ash. Several design mixes were considered. The design mixes consisted of varying amounts of FGD material, cement, lime, and water. The mixes were tested in the laboratory for flowability, unit weight, moisture content, unconfined compressive strength, erodibility, set-time, penetration, and long-term strength characteristics. Tests were conducted for up to 90 d of curing. Without any additives, the FGD material was observed to be as good as a regular (normal set) flowable fill in terms of placeability, unconfined compressive strength, and diggability. FGD material flowable fill with additives and admixtures compares favorably with the characteristics of conventional quick set flowable fills.

Polychlorinated Biphenyl Transport from Consolidation of Contaminated Sediments During In Situ Capping

The management of sediments contaminated with polychlorinated biphenyls (PCBs) is an issue of significant contemporary concern. The application of an in situ cap to isolate and contain the contaminants is a desirable management option that is hindered by a lack of detailed information regarding the fate of the contaminants after cap installation. In this study, we evaluate the fate and transport of PCBs in fine-grained, organic-rich sediments during and after the application of an in situ cap, with the goal of estimating the release of dissolved and colloid-bound contaminants from consolidating sediments under a variety of capping scenarios. Three capping materials were evaluated for their propensity to hinder PCB release; quartz sand, activated carbon, and a proprietary organoclay. Consolidation tests to simulate in situ rapid dewatering were conducted using contaminated sediment dredged from the Grand Calumet River in Gary, Indiana. The results of tests conducted without a cap indicate that rapid transient flow caused by consolidation results in the release of colloid-bound PCBs at concentrations exceeding 10 μg total PCBs per liter of effluent pore fluid, which was far above the calculated dissolved PCB concentration. Tests conducted to simulate release from capped sediments showed all three capping materials reduced the release of particles and associated PCBs by over 80 %. The dissolved organic carbon content also decreased significantly. The organoclay and activated carbon were more effective than sand for both particle and PCB removal. This work demonstrates that reactive caps help to mitigate contaminant release due to sediment consolidation and should be considered as a viable management option for in situ remediation of PCB-contaminated sediments.

An Experimental Investigation of Consolidation-Induced Solute Transport

This paper presents the results of an experimental investigation of consolidation-induced solute transport. Diffusion and large strain consolidation tests were conducted on composite specimens of kaolinite slurry consisting of an upper uncontaminated layer and a lower layer contaminated with potassium bromide. Solute breakthrough curves and final concentration profiles indicate that both diffusion and consolidation-induced advection can make important contributions to solute transport and that faster consolidation can increase the rate of solute mass outflow. The results of this study indicate that transient advection effects should be considered for transport analyses involving the large strain consolidation of soft contaminated clays.