The Effect of Variability in Hydraulic Conductivity on Contaminant Transport through Soil–Bentonite Cutoff Walls

Britton, J. P.; Filz, George M.; Little, John C.

doi:10.1061/(asce)1090-0241(2005)131:8(951)

Cited by 17 publications

(11 citation statements)

References 6 publications

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“…Two hydraulic scenarios 19,41 were considered (see Figure 4): Hydraulic Scenario 1 (HS1, Figure 4A): the hydraulic head in the polluted area is greater than at the outlet, and their difference is

Δ h = h_{o u t} - h_{i n} < 0

. In this scenario, the boundary conditions are such that both the advective and the diffusive fluxes are in the same direction in the absence of the well, that is, from the contaminated area to the aquifer.…”

Section: Scenarios Analyzed In the Numerical Simulationsmentioning

confidence: 99%

“…Specifications in the UK 12 require the hydraulic conductivity of the backfill material at 90 days to be less than

10^{- 9}

m/s for at least 80% of laboratory cured samples. However, the hydraulic conductivity of the barrier in the field depends on many factors which, in general, cause it to be higher than the one measured in the laboratory 6,9,13–20 . The complexity and the variability of these factors, ‐that is, as defects and fractures related to the construction, to the oscillation of the groundwater level and interaction with the atmosphere, chemical changes in the material fabric due to the aggressive ground conditions—imply that an a priori estimate of the in situ hydraulic conductivity is not possible, even if laboratory test results are available 21–23…”

Section: Introductionmentioning

confidence: 99%

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A procedure to estimate cutoff wall transport properties from monitoring wells

Guida

Musso

Sanetti

et al. 2021

Num Anal Meth Geomechanics

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Owing to their capability in limiting the transport of pollutants in the subsoil, cutoff walls are popular solutions for the confinement of contaminants. These barriers are often made of soil‐bentonite or cement‐bentonite mixtures, which are characterized by low hydraulic conductivity, low hydrodynamic dispersion, and long‐term durability. However, the aggressive chemical environment to which these walls are subjected might negatively impact on their performance. Assessment of their performance with time is thus a crucial issue in wall design. The use of dedicated monitoring wells, cast in place inside the wall during construction when the bentonitic mixture is still fluid, can be particularly suitable for both intercepting and detecting the fluids flowing through the barrier. In this research, the results of a numerical study aimed at providing a methodology to estimate the transport properties of the backfill material at the site scale are presented. The methodology relies on abaci and only requires (i) flow and concentration of contaminant data within a monitoring well inside the barrier and (ii) hydraulic head at inlet and outlet of the barrier to be known.

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Δ h = h_{o u t} - h_{i n} < 0

Section: Scenarios Analyzed In the Numerical Simulationsmentioning

confidence: 99%

“…Specifications in the UK 12 require the hydraulic conductivity of the backfill material at 90 days to be less than

10^{- 9}

Section: Introductionmentioning

confidence: 99%

A procedure to estimate cutoff wall transport properties from monitoring wells

Guida

Musso

Sanetti

et al. 2021

Num Anal Meth Geomechanics

View full text Add to dashboard Cite

show abstract

“…This algorithm was found to be reasonably accurate compared to RFEM (10-30% relative error), for calculation durations of only 1/10 3 -1/10 2 times those for RFEM. However, this algorithm is only applicable to steady-state problems, whereas time-dependent behavior is of significant engineering interest in many applications, such as in the evaluation of the breakthrough time of leachate through a cutoff wall in a landfill project 4,14,15,41 and the leakage detection of a cutoff wall in a deep excavation. 20,22,23 In such cases, a transient-state analysis is more relevant than a steady-state analysis.…”

Section: F I G U R Ementioning

confidence: 99%

“…Underground cutoff walls are widely used in various applications to hinder groundwater flow, contaminant transport, and possibly heat conduction 1–9 . Depending on the intended function, site conditions, and budget, cutoff walls are constructed by many different approaches.…”

Section: Introductionmentioning

confidence: 99%

An efficient transient‐state algorithm for evaluation of leakage through defective cutoff walls

Pan

Hicks

Broere

2020

Num Anal Meth Geomechanics

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Artificial barriers are widely used to prevent leakages. However, due to construction errors during the wall installation, passages with small dimensions may occasionally penetrate through the barrier, undermining its tightness. A three-dimensional discretized algorithm (TDA) is proposed for quantitatively estimating the transient-state discharge rate through defective cutoff walls. By discretizing the wall into a three-dimensional refined mesh grid, the algorithm enables an examination of penetrating passages, an evaluation of defect dimensions, and an estimation of discharge rate through the penetrating passages. A rigorous realization-by-realization comparison between the TDA and the finite element method (FEM) was made, and it was found that the TDA results show strong correlations with the FEM results, but at a remarkably lower (1/10 3-1/10 4) computational cost. The TDA generally gives a discharge rate that is 0.1-1.0 times greater than its FEM counterpart, as the lengthened seepage distance due to random corrugations in the penetrating untreated zone cannot be replicated by the TDA.

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“…With the development of society, anti-seepage projects are increasing, such as cutoff walls, continuous walls, and cutoff bodies in underground spaces [1,2]. Seepage indices mainly include the seepage coefficient and seepage gradient, which are important indices reflecting the permeability of materials.…”

Section: Introductionmentioning

confidence: 99%

Simple Fully Automatic Testing Method of Seepage Indices for Low-Permeability Materials

Shen

Wang³

2021

Water

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In anti-seepage engineering, quality control and engineering applications are based on the accurate measurement of seepage indices for low-permeability materials. The test used to determine the seepage indices for low-permeability materials adopts an external source to produce water pressure, and the seepage flux produced during the process requires manual measurement; thus, the apparatus used is complex and difficult to operate, thereby lowering the testing efficiency and restricting its application. In this study, a built-in servo motor was used to produce high water pressure with a pressure transmitter, and it controlled and measured the seepage pressure. According to the rotation number of the electric cylinder motor, the volume change of water in the hydraulic cylinder was calculated and, thus, the seepage flux was deduced. A simple fully automatic seepage apparatus for low-permeability materials was designed with a human–computer interface. The results showed the successful calculation of seepage flux as a function of the rotation number of the servo motor through automatic measurement. Furthermore, the replacement of the external high-pressure source with the built-in servo motor enhanced the safety performance, and the human–computer interface enabled an interactive operation and simplified the measurement structure. This simple testing method can provide technical support for quality inspection and construction control of anti-seepage engineering.

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The Effect of Variability in Hydraulic Conductivity on Contaminant Transport through Soil–Bentonite Cutoff Walls

Cited by 17 publications

References 6 publications

A procedure to estimate cutoff wall transport properties from monitoring wells

A procedure to estimate cutoff wall transport properties from monitoring wells

An efficient transient‐state algorithm for evaluation of leakage through defective cutoff walls

Simple Fully Automatic Testing Method of Seepage Indices for Low-Permeability Materials

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