Case Study: Construction and<i>In Situ</i>Hydraulic Conductivity Evaluation of a Deep Soil-Cement-Bentonite Cutoff Wall

Ruffing, Daniel; Evans, Jeffrey

doi:10.1061/9780784413272.180

Cited by 10 publications

(8 citation statements)

References 3 publications

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“…Additional dry bentonite can be added to the soil-cement-bentonite mixture to reach the target slump height (Ryan and Day 2002), and (2) mixing OPC-water grout (weight ratio = 1: 1) with in-site soil and prehydrated bentonite slurry (Ruffing and Evans 2014). Nevertheless, neither method can prevent the attack of high pH of OPC to the bentonite or cation exchange reactions between free cations (e.g., Ca 2+ ) in the hydrated OPC and readily exchangeable cations in the bentonite (e.g., Na + ).…”

Section: Limitations Of Current Studymentioning

confidence: 99%

Engineering Properties of Vertical Cutoff Walls Consisting of Reactive Magnesia-Activated Slag and Bentonite: Workability, Strength, and Hydraulic Conductivity

Hao

Jin

et al. 2019

J. Mater. Civ. Eng.

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The soil-cement-bentonite (SCB) vertical cutoff walls are commonly used to control flow of contaminated groundwater in polluted sites. However, conventional backfill consisting of Ordinary Portland cement (OPC) is associated with relatively high CO2 footprint. Potential chemical interactions between OPC and bentonite could also undermine the long-term durability of SCB materials. In this paper, we propose an innovative backfill material for cutoff walls, which is composed of MgO-activated ground granulated blast furnace slag (GGBS), bentonite and soil. The OPC-soil, OPC-bentonite-soil, and OPC-GGBS-bentonite-soil backfill materials are also tested for comparison purpose. Workability of the fresh backfills and unconfined compressive strength of aged backfills are investigated. The hydraulic conductivities of aged backfills permeated with tap water, Na2SO4 and Pb-Zn solutions are assessed. The unconfined compressive strength and hydraulic conductivity of the proposed backfill permeated with tap water for the backfills are in the range of 230-520 kPa and 1.1×10-10-6.3×10-10 m/s at 90-day-curing, respectively, depending on the mix composition. The hydraulic conductivity of the proposed MgO-GGBS-bentonite-soil backfill permeated with sodium sulfate (Na2SO4) or lead-zinc (Pb-Zn) solution is well below the commonly used limit, while the OPC-bentonite-soil backfill shows a significant loss in its impermeability. Environmental and economic analyses indicate that, compared with the conventional backfill made from the OPC-bentonite-soil mixture, the proposed backfill reduces approximately 84.7%-85.1% in CO2 emissions and 15.3%-16.9% cost. The environmental and economic advantages will 3 promote the utilization of MgO-activated GGBS-bentonite mixtures in the cutoff walls and further advocate its application in land remediation projects.

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Section: Limitations Of Current Studymentioning

confidence: 99%

Engineering Properties of Vertical Cutoff Walls Consisting of Reactive Magnesia-Activated Slag and Bentonite: Workability, Strength, and Hydraulic Conductivity

Hao

Jin

et al. 2019

J. Mater. Civ. Eng.

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“…In general, the applicability of slurry walls is limited by the depth of installation, which is approximately 30.5 m below ground surface. However, site-specific and technology-specific considerations may limit this depth to shallower installations, but in certain cases, the depth can even be increased beyond 30.5 m; a depth of up to 56 m has been documented for a soil-cement-bentonite cutoff wall (Ruffing and Evans, 2014).…”

Section: Slurry or Barrier Wallsmentioning

confidence: 99%

Conceptual Groundwater Remedial Alternatives at Coal Combustion Residuals Sites

Goldemund

Ahrens

2019

Coal Combustion and Gasification Products

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Groundwater below many basins that have been used to store coal combustion residuals (CCRs) may have concentrations of certain inorganic constituents in excess of applicable regulatory standards. Given that many inorganic CCR constituents are also naturally occurring in the aquifer matrix, their detection may not always be indicative of a release from the CCR unit. Inorganics may be present at elevated levels in groundwater due to natural or background conditions, or due to changes to the aquifer geochemistry resulting from the presence of the CCR basin, which then mobilizes these naturally occurring constituents beneath the CCR unit. Care must be taken to identify the source(s) and the release mechanism(s) of potential CCRrelated impacts. If a link between a CCR unit and an inorganic groundwater exceedance has been established, stakeholders may be faced with the need to evaluate groundwater remedial alternatives to address these impacts. This paper conceptually discusses potentially applicable remedial approaches, including (i) monitored natural attenuation, (ii) hydraulic control using ex situ and in situ methods, (iii) permeable reactive barriers, (iv) slurry walls, and (v) oxidation-reduction-altering approaches. Additionally, this article explores potential water reuse options available at many power generating stations.

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“…Observations differ for the analysis of the mechanism; however, the results of all approaches indicate that the stress state in the trench (below the depth of 5-7 m) remains lower than the geostatic approach. It has been suggested that the major principal stress in deep-narrow slurry walls is horizontal, and it is vertical in shallow-wide slurry walls [5,9,8]. However, the specific mechanism behind the lateral squeezing models [9,5] has not been fully addressed for modeling of one sort or another.…”

Section: Introductionmentioning

confidence: 99%

Lateral squeezing effects on cement-slag-bentonite slurry wall performance

Talefirouz

Çokça

2021

Materials and Geoenvironment

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Cement-slag-bentonite slurry walls are self-hardening structures, and they are mainly used to retard contamination transport into the groundwater stream. Whilst permeability of a mixture is an initial criterion in slurry wall design and material selection, long-term performance is mainly influenced by curing ages and stress-state caused by adjacent soil. In this study, the steady-state of effective stresses at 7 days and 28 days of curing age is predicted. The effect of the modulus of horizontal subgrade reaction, interface friction, and transition of the earth pressure from at-rest to the active condition was applied to develop the model. Unlike the quantities that the geostatic model presented, this method gives a slight decrease of stresses after a certain depth, and the trend is in good agreement with trends provided by previous studies. Furthermore, the predicted stresses are then applied to estimate the permeability of the wall at each depth and compare it with those obtained in the laboratory. Finally, predicted effective stresses stay lower than geostatic stress, and the slurry wall consolidation along with the sidewalls’ lateral squeezing leads to keeping the stress state under control.

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Case Study: Construction andIn SituHydraulic Conductivity Evaluation of a Deep Soil-Cement-Bentonite Cutoff Wall

Cited by 10 publications

References 3 publications

Engineering Properties of Vertical Cutoff Walls Consisting of Reactive Magnesia-Activated Slag and Bentonite: Workability, Strength, and Hydraulic Conductivity

Engineering Properties of Vertical Cutoff Walls Consisting of Reactive Magnesia-Activated Slag and Bentonite: Workability, Strength, and Hydraulic Conductivity

Conceptual Groundwater Remedial Alternatives at Coal Combustion Residuals Sites

Lateral squeezing effects on cement-slag-bentonite slurry wall performance

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