Cutoff Wall

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Hangseok Choi - One of the best experts on this subject based on the ideXlab platform.

  • Analytical solution for transient groundwater flow during slug test in vertical Cutoff Walls
    International Journal for Numerical and Analytical Methods in Geomechanics, 2014
    Co-Authors: Jeehee Lim, Dongseop Lee, Hyun Jun Choi, Hangseok Choi
    Abstract:

    SUMMARY An analysis method for transient groundwater flow during slug tests performed in vertical Cutoff Walls is presented. The analytical solution for evaluating hydraulic conductivity of vertical Cutoff Walls is derived by applying the method of images to the previously developed analytical solution that is exclusively applicable to an infinite aquifer. Two distinct boundary conditions are considered to account for the configuration of the vertical Cutoff Wall: the Wall-soil formation interfaces with or without the existence of filter cakes, that is, constant-head boundary and no-flux boundary conditions. A series of type curves is constructed from the analytical solution and compared with those of a partially penetrated well within an aquifer. The constant-head boundary condition provides faster hydraulic head recovery than the aquifer case. On the other hand, the no-flux boundary condition leads to a delayed hydraulic head recovery. The greater the shape factor and well offset from the center of the Cutoff Wall, and the smaller the width of the Cutoff Wall, the greater the effect of the boundary condition observed in the type curves. This result shows the significance of considering proper boundary conditions at the vertical Cutoff Wall in analyzing slug tests. Copyright © 2014 John Wiley & Sons, Ltd.

  • Analytical Interpretation of Slug Test in a Vertical Cutoff Wall
    Ground Water, 2013
    Co-Authors: Jeehee Lim, Dongseop Lee, Vitaly A. Zlotnik, Hangseok Choi
    Abstract:

    An analysis method for slug tests performed in a partially penetrating well within a vertical Cutoff Wall is presented. A steady-state shape factor for evaluating hydraulic conductivity of the material within the Wall was derived by applying the method of images to the previously developed analytical solution of Zlotnik et al. (2010) for an infinite aquifer. Two distinct boundary conditions were considered: constant-head boundary for the case of direct contact between the Wall and the aquifer, and no-flux boundary representing an impermeable filter cake on the sides of the Wall. The constant-head and no-flux boundary conditions yield significantly higher and lower shape factors, respectively, than those for the infinite aquifer. Consequently the conventional line-fitting method for slug test analysis would yield an inaccurate estimate of the hydraulic conductivity of a vertical Cutoff Wall.

  • Hydraulic Characteristics of Bentonite Cake Fabricated on Cutoff Walls
    Clays and Clay Minerals, 2012
    Co-Authors: The-bao Nguyen, Chul-ho Lee, Jeehee Lim, Hangseok Choi
    Abstract:

    Bentonite cake is usually formed on the excavated trench surface that is supported by the bentonite slurry during construction of slurry Cutoff Walls. The lower hydraulic conductivity of bentonite cakes formed during construction of slurry Cutoff Walls in comparison to backfill materials provides an additional benefit. In the present study, the hydraulic conductivities of bentonite cakes made using three different bentonites were estimated using the modified fluid-loss test under various pressures. Both the hydraulic conductivities of bentonite cakes and Cutoff-Wall backfill are important in evaluating the in situ hydraulic performance of slurry Cutoff-Wall construction. Three bentonite slurry concentrations of 4, 6, and 8% were used to fabricate bentonite cakes that represent common field conditions. X-ray diffraction, cation exchange capacity, and swell-index data were collected to characterize the bentonites. Two modified methods for analyzing fluid-loss test results were used to estimate bentonite cake hydraulic conductivities. In addition, the viscosity as a function of time was measured to explain the sealing capacities of the bentonite slurries. The bentonite-cake hydraulic conductivities ranged from 2.15×10^−11 m/s to 2.88×10^−10 m/s, which were 10 to 500 times lower than the Cutoff Wall backfill design. Experimental results for 4 and 6% bentonite slurries were relatively similar, but the 8% slurries were noticeably different. Calculated bentonite-cake thickness and stress distribution indicated that the local void ratio and hydraulic conductivity may vary across the cake thickness. The considerably lower bentonite-cake hydraulic conductivities compared to the Cutoff Wall backfill design show its significance in slurry Cutoff-Wall construction practices.

  • slug test analysis in vertical Cutoff Walls with consideration of filter cake
    Journal of Geotechnical and Geoenvironmental Engineering, 2011
    Co-Authors: The-bao Nguyen, Hangseok Choi
    Abstract:

    In constructing a vertical Cutoff Wall, bentonite-water slurry is frequently used to maintain the stability of sideWalls during excavation before backfilling the trench with less permeable materials to complete the Cutoff Wall construction. This procedure leads to a thin but relatively impermeable layer, called a filter cake, on the excavation surface. The aim of this paper is to examine the effect of a filter cake on evaluating hydraulic conductivity of the Cutoff Wall backfill through a slug test analysis with the aid of the verified numerical program, Slug_3D. As an upper bound solution for evaluation of the hydraulic conductivity of the Cutoff Wall backfill, no-flux boundary conditions for the boundaries of Cutoff Walls are imposed to consider the effect of filter cakes. The type-curve method and modified line-fitting method are employed to reanalyze the case of EMCON/OWT, Inc., as an example. The previous analysis, without consideration of a filter cake, is compared with the current results that cons...

  • Modification of the Bouwer and Rice method to a Cutoff Wall with a filter cake.
    Ground Water, 2010
    Co-Authors: The-bao Nguyen, Chul-ho Lee, Se-won Kim, Hangseok Choi
    Abstract:

    The Bouwer and Rice method is a line-fitting method used to estimate the hydraulic conductivity of an aquifer by means of a slug test. When considering a relatively impermeable layer, called a filter cake, which may form at the interface between a Cutoff Wall and the natural soil formation, the assumptions of the Bouwer and Rice method are violated. A modification of the Bouwer and Rice method is proposed that incorporates the concept of a flow net, whereby the geometry of the Cutoff Wall and filter cake is effectively considered in estimating the hydraulic conductivity of a vertical Cutoff Wall.

Akira Ishikawa - One of the best experts on this subject based on the ideXlab platform.

  • Multi-aquifer pumping test to determine Cutoff Wall length for groundwater flow control during site excavation in Tokyo, Japan
    Hydrogeology Journal, 2008
    Co-Authors: Noriharu Miyake, Nobuaki Kohsaka, Akira Ishikawa
    Abstract:

    Se han llevado a cabo ensayos de bombeo en acuíferos multicapa, utilizando bombeos en pozos con varias rejillas y piezómetros multicapa, para controlar el flujo de agua subterránea en una excavación a gran escala en Tokio, Japón. El lugar estaba conformado por acuíferos confinados multi-capa. En los ensayos, el bombeo se llevó a cabo utilizando el bombeo en un pozo multiacuífero en el que la profundidad de la rejilla fue elegida arbitrariamente. Se midieron los cambios en las presiones de cada acuífero en cada posición de la rejilla en el pozo de bombeo multiacuífero. Se estimó la conductividad hidráulica ( K ) y el coeficiente de almacenamiento ( S _s) no solamente de los acuíferos, sino también de las capas de baja permeabilidad entre los acuíferos, mediante el método de Cooper-Jacob, y se calibró un modelo de aguas subterráneas de elementos finitos (FEM). Cuatro muros de corte de diferente longitud fueron supuestos para la profundidad final de la excavación, y se obtuvieron correlaciones entre la longitud del muro, la descarga del bombeo y el descenso en la parte trasera del muro de corte fueron obtenidos a partir de simulaciones utilizando parámetros de K y S _s en el modelo FEM. Entonces, se seleccionó la longitud de muro más conveniente basado en las correlaciones simuladas considerando la condición ambiental, el periodo de construcción y los costes del muro de corte. Multi-aquifer pumping tests, using a multi-screen pumping well and multi-level piezometers, were carried out for groundwater flow control in a large-scale excavation site in Tokyo, Japan. The site was underlain by multi-layered confined aquifers. In the tests, pumping was carried out using a multi-aquifer pumping well in which a screen depth was chosen arbitrarily. Changes in groundwater pressure heads in each aquifer were measured at each screen position of the multi-aquifer pumping well. Hydraulic conductivity ( K ) and specific storage ( S _s) of not only aquifers, but also for low permeability layers between the aquifers, were estimated using the Cooper-Jacob method, and calibrated by a finite element method (FEM) groundwater model. Four different Cutoff Wall lengths were assumed for final excavation depth, and correlations among Wall length, pumping discharge and drawdown at the back of the Cutoff Wall were obtained from simulations using the K and S _s parameters in the FEM model. Then, the most suitable Wall length was selected based on the simulated correlations considering environmental condition, construction period and cost of the Cutoff Wall. Des essais de pompage sur plusieurs aquifères ont été réalisés à l’aide d’un puits de pompage équipé de plusieurs zones crépinées et de piézomètres mesurant des niveaux différents, afin de contrôler l’écoulement des eaux souterraines au niveau d’un grand site d’excavation à Tokyo au Japon. Le site recouvre des aquifères captifs multi-couches. Pour les tests, le pompage a été effectué en utilisant un puits de pompage multi-aquifères dans lequel la profondeur de la crépine a été choisi arbitrairement. Les changements des niveaux piézomètriques de l’eau souterraine dans chaque aquifère ont été mesurés pour chaque position de la crépine du puits de pompage multi-aquifères. Les valeurs de conductivité hydraulique ( K ) et d’emmagasinement ( S _s) des aquifères, mais aussi celles des couches à faibles perméabilités situées entre les aquifères, ont été estimées en utilisant la méthode de Cooper-Jacob, et calibrées dans un modèle hydrogéologique aux éléments finis (FEM en anglais). Quatre longueurs différentes de mur de tranchée ont été envisagées pour la profondeur finale de l’excavation, et les corrélations entre la longueur du mur, le débit de pompage et le rabattement en arrière du mur ont été obtenues à partir de simulations utilisant les valeurs de K et de S _s du modèle aux éléments finis. Puis, la longueur du mur de tranchée la mieux adaptée a été sélectionnée en fonction des corrélations simulées en prenant en compte les conditions environnementales, la période de construction et le coût du mur de tranchée.

  • multi aquifer pumping test to determine Cutoff Wall length for groundwater flow control during site excavation in tokyo japan
    Hydrogeology Journal, 2008
    Co-Authors: Noriharu Miyake, Nobuaki Kohsaka, Akira Ishikawa
    Abstract:

    Multi-aquifer pumping tests, using a multi-screen pumping well and multi-level piezometers, were carried out for groundwater flow control in a large-scale excavation site in Tokyo, Japan. The site was underlain by multi-layered confined aquifers. In the tests, pumping was carried out using a multi-aquifer pumping well in which a screen depth was chosen arbitrarily. Changes in groundwater pressure heads in each aquifer were measured at each screen position of the multi-aquifer pumping well. Hydraulic conductivity (K) and specific storage (Ss) of not only aquifers, but also for low permeability layers between the aquifers, were estimated using the Cooper-Jacob method, and calibrated by a finite element method (FEM) groundwater model. Four different Cutoff Wall lengths were assumed for final excavation depth, and correlations among Wall length, pumping discharge and drawdown at the back of the Cutoff Wall were obtained from simulations using the K and Ss parameters in the FEM model. Then, the most suitable Wall length was selected based on the simulated correlations considering environmental condition, construction period and cost of the Cutoff Wall.

Jeffrey C. Evans - One of the best experts on this subject based on the ideXlab platform.

  • design and evaluation of iot enabled instrumentation for a soil bentonite slurry trench Cutoff Wall
    Infrastructures, 2019
    Co-Authors: Alan Marchiori, Jeffrey C. Evans
    Abstract:

    In this work, we describe our approach and experiences bringing an instrumented soil-bentonite slurry trench Cutoff Wall into a modern IoT data collection and visualization pipeline. Soil-bentonite slurry trench Cutoff Walls have long been used to control ground water flow and contaminant transport. A Raspberry Pi computer on site periodically downloads the sensor data over a serial interface from an industrial datalogger and transmits the data wirelessly to a gateway computer located 1.3 km away using a reliable transmission protocol. The resulting time-series data is stored in a MongoDB database and data is visualized in real-time by a custom web application. The system has been in operation for over two years achieving 99.42% reliability and no data loss from the collection, transport, or storage of data. This project demonstrates the successful bridging of legacy scientific instrumentation with modern IoT technologies and approaches to gain timely web-based data visualization facilitating rapid data analysis without negatively impacting data integrity or reliability. The instrumentation system has proven extremely useful in understanding the changes in the stress state over time and could be deployed elsewhere as a means of on-demand slurry trench Cutoff Wall structural health monitoring for real-time stress detection linked to hydraulic conductivity or adapted for other infrastructure monitoring applications.

  • case study construction and in situ hydraulic conductivity evaluation of a deep soil cement bentonite Cutoff Wall
    Geo-Congress 2014 Technical Papers: Geo-characterization and Modeling for Sustainability, 2014
    Co-Authors: D. G. Ruffing, Jeffrey C. Evans
    Abstract:

    This paper presents a case study of a deep soil-cement-bentonite (SCB) slurry trench Cutoff Wall constructed outside of Smithland, KY, in 2010. Installed to a maximum depth of 56 m, this Cutoff Wall is the deepest known seepage barrier installed using continuous trenching. The Wall was installed around the perimeter of a deep excavation to reduce long-term dewatering costs associated with construction of a hydroelectric power plant adjacent to the Ohio River. After Wall construction, a dewatering system was installed inside the area enclosed by the Wall to facilitate the deep excavation. Preconstruction design and construction details are presented along with the results of a post-construction assessment of the hydraulic conductivity ( k ) of the Wall. Steady-state groundwater flow measurements from the dewatering system coupled with information on the Wall thickness and water levels inside and outside of the Wall were used to obtain a large-scale estimate of the in situ k of the Wall. The in situ k was compared with laboratory k values measured for specimens prepared from grab samples of the as-mixed SCB backfill. Comparisons also were made to the target (design) k and the expected field mixed backfill k established during a preconstruction bench-scale study. The comparisons revealed that the in situ k is approximately one order of magnitude less than the design k and approximately equal to the average laboratory k measured from grab samples and the expected k from the results of the bench-scale study.

  • long term in situ measurements of the volumetric water content in a soil bentonite slurry trench Cutoff Wall
    GeoCongress 2012, 2012
    Co-Authors: D. G. Ruffing, Jeffrey C. Evans, Michael A Malusis
    Abstract:

    This paper presents the results of a field study to assess post-construction changes in the volumetric water content () of a soil-bentonite (SB) slurry trench Cutoff Wall. Time domain reflectometry (TDR) sensors were installed in a newly-constructed SB Cutoff Wall in the summer of 2008 and were used to monitor  as a function of depth within the SB backfill for approximately one year. The methods used to install the probes are described and the measured  distributions are presented and discussed. A general trend of decreasing  with time was observed at all sensor locations. Decreases in  within the portion of the Wall below the water table are attributed to backfill consolidation, whereas the larger decreases in  near the top of the Wall (above the water table) are likely due to a combination of backfill consolidation and backfill drying. A field sampling program is recommended to confirm the moisture profiles obtained from the TDR sensors.

  • In Situ Evaluation of a Shallow Soil Bentonite Slurry Trench Cutoff Wall
    2010
    Co-Authors: D. G. Ruffing, Jeffrey C. Evans
    Abstract:

    Soil bentonite (SB) slurry trench Cutoff Walls have been widely used in the USA to control ground water flow and the migration of contaminants in the ground water. While substantial laboratory testing has been conducted, field studies are limited. Researchers at Bucknell University were afforded the opportunity to conduct a suite of in situ tests on a SB Cutoff Wall constructed during the summer of 2008. Cutoff Wall properties were measured in situ employing cone penetration tests (CPT), Marchetti dilatometer tests (DMT), vane shear tests (VST), and ground water level monitoring on both sides of the Wall. Tests were conducted during construction and at times of 3 months, 6 months and 9 months after construction to evaluate the change in Wall properties with time. In addition, bulk samples and a Shelby tube SB backfill sample were obtained during construction for laboratory testing which included water content, grain size distribution, consolidation and rigid Wall hydraulic conductivity. The field and laboratory data were analyzed to develop a consistent understanding of the in situ properties of the Cutoff Wall backfill. The VST and CPT showed an increase in backfill shear strength over the time-frame of the study. A slight increase of shear strength with depth was also found. However, a comparison of shear strength measured compared with that predicted using typical ratios of strength to consolidation stress indicated that the in situ stress is less than that expected. Laboratory testing revealed a decreasing hydraulic conductivity with increasing consolidation stress demonstrating the importance of a reliable estimation of the stress state in the Wall.

  • a miniature cone for measuring the slump of soil bentonite Cutoff Wall backfill
    Geotechnical Testing Journal, 2008
    Co-Authors: Michael A Malusis, Jeffrey C. Evans, Michael H Mclane, Nikki R Woodward
    Abstract:

    Measurement of slump for soil-bentonite (SB) Cutoff Wall backfill using a standard ASTM C143-00 slump cone is widely employed to design SB backfill for workability and to evaluate field backfill quality during Cutoff Wall construction. The standard cone is particularly suitable for field testing, where large backfill quantities are available, but is less practical for laboratory testing of backfills during design. This paper describes the development and evaluation of a miniature slump cone that requires only ∼16 % of the backfill volume required for the standard cone. Results of slump tests performed on three model SB backfills with different solid compositions indicate that the miniature cone provides reproducibility similar to that given by the standard cone when the backfills are prepared to a standard slump of 100 mm to 200 mm. The empirical relationship between standard slump (SS) and miniature slump (SM) for all three model backfills is represented accurately by a single linear expression (i.e., SS=60+1.8SM, where SS and SM are in millimetres) that is nearly identical to the predicted correlation given by an analytical slump cone model (i.e., SS=64+1.8SM) for the range 100⩽SS⩽200 mm.

Evans, Jeffrey C. - One of the best experts on this subject based on the ideXlab platform.

Noriharu Miyake - One of the best experts on this subject based on the ideXlab platform.

  • Multi-aquifer pumping test to determine Cutoff Wall length for groundwater flow control during site excavation in Tokyo, Japan
    Hydrogeology Journal, 2008
    Co-Authors: Noriharu Miyake, Nobuaki Kohsaka, Akira Ishikawa
    Abstract:

    Se han llevado a cabo ensayos de bombeo en acuíferos multicapa, utilizando bombeos en pozos con varias rejillas y piezómetros multicapa, para controlar el flujo de agua subterránea en una excavación a gran escala en Tokio, Japón. El lugar estaba conformado por acuíferos confinados multi-capa. En los ensayos, el bombeo se llevó a cabo utilizando el bombeo en un pozo multiacuífero en el que la profundidad de la rejilla fue elegida arbitrariamente. Se midieron los cambios en las presiones de cada acuífero en cada posición de la rejilla en el pozo de bombeo multiacuífero. Se estimó la conductividad hidráulica ( K ) y el coeficiente de almacenamiento ( S _s) no solamente de los acuíferos, sino también de las capas de baja permeabilidad entre los acuíferos, mediante el método de Cooper-Jacob, y se calibró un modelo de aguas subterráneas de elementos finitos (FEM). Cuatro muros de corte de diferente longitud fueron supuestos para la profundidad final de la excavación, y se obtuvieron correlaciones entre la longitud del muro, la descarga del bombeo y el descenso en la parte trasera del muro de corte fueron obtenidos a partir de simulaciones utilizando parámetros de K y S _s en el modelo FEM. Entonces, se seleccionó la longitud de muro más conveniente basado en las correlaciones simuladas considerando la condición ambiental, el periodo de construcción y los costes del muro de corte. Multi-aquifer pumping tests, using a multi-screen pumping well and multi-level piezometers, were carried out for groundwater flow control in a large-scale excavation site in Tokyo, Japan. The site was underlain by multi-layered confined aquifers. In the tests, pumping was carried out using a multi-aquifer pumping well in which a screen depth was chosen arbitrarily. Changes in groundwater pressure heads in each aquifer were measured at each screen position of the multi-aquifer pumping well. Hydraulic conductivity ( K ) and specific storage ( S _s) of not only aquifers, but also for low permeability layers between the aquifers, were estimated using the Cooper-Jacob method, and calibrated by a finite element method (FEM) groundwater model. Four different Cutoff Wall lengths were assumed for final excavation depth, and correlations among Wall length, pumping discharge and drawdown at the back of the Cutoff Wall were obtained from simulations using the K and S _s parameters in the FEM model. Then, the most suitable Wall length was selected based on the simulated correlations considering environmental condition, construction period and cost of the Cutoff Wall. Des essais de pompage sur plusieurs aquifères ont été réalisés à l’aide d’un puits de pompage équipé de plusieurs zones crépinées et de piézomètres mesurant des niveaux différents, afin de contrôler l’écoulement des eaux souterraines au niveau d’un grand site d’excavation à Tokyo au Japon. Le site recouvre des aquifères captifs multi-couches. Pour les tests, le pompage a été effectué en utilisant un puits de pompage multi-aquifères dans lequel la profondeur de la crépine a été choisi arbitrairement. Les changements des niveaux piézomètriques de l’eau souterraine dans chaque aquifère ont été mesurés pour chaque position de la crépine du puits de pompage multi-aquifères. Les valeurs de conductivité hydraulique ( K ) et d’emmagasinement ( S _s) des aquifères, mais aussi celles des couches à faibles perméabilités situées entre les aquifères, ont été estimées en utilisant la méthode de Cooper-Jacob, et calibrées dans un modèle hydrogéologique aux éléments finis (FEM en anglais). Quatre longueurs différentes de mur de tranchée ont été envisagées pour la profondeur finale de l’excavation, et les corrélations entre la longueur du mur, le débit de pompage et le rabattement en arrière du mur ont été obtenues à partir de simulations utilisant les valeurs de K et de S _s du modèle aux éléments finis. Puis, la longueur du mur de tranchée la mieux adaptée a été sélectionnée en fonction des corrélations simulées en prenant en compte les conditions environnementales, la période de construction et le coût du mur de tranchée.

  • multi aquifer pumping test to determine Cutoff Wall length for groundwater flow control during site excavation in tokyo japan
    Hydrogeology Journal, 2008
    Co-Authors: Noriharu Miyake, Nobuaki Kohsaka, Akira Ishikawa
    Abstract:

    Multi-aquifer pumping tests, using a multi-screen pumping well and multi-level piezometers, were carried out for groundwater flow control in a large-scale excavation site in Tokyo, Japan. The site was underlain by multi-layered confined aquifers. In the tests, pumping was carried out using a multi-aquifer pumping well in which a screen depth was chosen arbitrarily. Changes in groundwater pressure heads in each aquifer were measured at each screen position of the multi-aquifer pumping well. Hydraulic conductivity (K) and specific storage (Ss) of not only aquifers, but also for low permeability layers between the aquifers, were estimated using the Cooper-Jacob method, and calibrated by a finite element method (FEM) groundwater model. Four different Cutoff Wall lengths were assumed for final excavation depth, and correlations among Wall length, pumping discharge and drawdown at the back of the Cutoff Wall were obtained from simulations using the K and Ss parameters in the FEM model. Then, the most suitable Wall length was selected based on the simulated correlations considering environmental condition, construction period and cost of the Cutoff Wall.

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