An analytical model for the control of silica grout penetration in natural groundwater systems

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Abstract

Over the last three decades, colloidal silica has been investigated and more recently adopted as a low viscosity grouting technology (e.g. for grouting rock fractures within geological disposal facilities nuclear waste). The potential of colloidal silica as a favourable grouting material exists due to: its initial low viscosity; its low hydraulic conductivity after gelling (of the order of 10-7 cm/s); the very low injection pressures required; its controllable set/gel times (from minutes to several days); the fact it is environmentally inert; its small particle size (less than hundreds of nanometres) and its cost-effectiveness. Despite the documented success of colloidal silica based grouts for hydraulic barrier formation, research has not translated into widespread industrial use. A key factor in this limited commercial uptake is the lack of a predictive model for grout gelling which controls grout penetration: whilst data are available to underpin design of a grouting campaign in laboratory conditions, little research has been done to underpin applications in natural environments. Here we develop and validate an analytical model of colloidal silica gelling in groundwaters with varying pH and background electrolyte concentrations. This paper presents an analytical model that accounts for changes in pH, electrolyte concentration, cation valency and molar mass, silica particle size and silica concentration giving predictive capability without the need for site-specific calibration. The model is validated against experimental observations for gel times of 32 minutes to 766 minutes, the model accurately predicts the log(gel time) with an average error of 4% which corresponds to an R2 value of 0.96 The model is then applied to a hypothetical case study to demonstrate its use in grout design, based on published in-situ groundwater data from the Olkiluoto area of Finland. The model successfully predicts the required accelerator concentration to achieve a grout gel time of approximately 50 minutes, taking into account the cations already present within the synthetic groundwater.
LanguageEnglish
Pages105-113
Number of pages9
JournalTunnelling and Underground Space Technology
Volume70
Early online date2 Aug 2017
DOIs
Publication statusPublished - 30 Nov 2017

Fingerprint

grout
Groundwater
Analytical models
penetration
Grouting
silica
Silica
grouting
groundwater
Gels
gel
electrolyte
Positive ions
Particle size
Electrolytes
Viscosity
viscosity
cation
particle size
Molar mass

Keywords

  • colloidal silica
  • grouting
  • injection
  • groundwater chemistry
  • viscosity
  • gel time

Cite this

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title = "An analytical model for the control of silica grout penetration in natural groundwater systems",
abstract = "Over the last three decades, colloidal silica has been investigated and more recently adopted as a low viscosity grouting technology (e.g. for grouting rock fractures within geological disposal facilities nuclear waste). The potential of colloidal silica as a favourable grouting material exists due to: its initial low viscosity; its low hydraulic conductivity after gelling (of the order of 10-7 cm/s); the very low injection pressures required; its controllable set/gel times (from minutes to several days); the fact it is environmentally inert; its small particle size (less than hundreds of nanometres) and its cost-effectiveness. Despite the documented success of colloidal silica based grouts for hydraulic barrier formation, research has not translated into widespread industrial use. A key factor in this limited commercial uptake is the lack of a predictive model for grout gelling which controls grout penetration: whilst data are available to underpin design of a grouting campaign in laboratory conditions, little research has been done to underpin applications in natural environments. Here we develop and validate an analytical model of colloidal silica gelling in groundwaters with varying pH and background electrolyte concentrations. This paper presents an analytical model that accounts for changes in pH, electrolyte concentration, cation valency and molar mass, silica particle size and silica concentration giving predictive capability without the need for site-specific calibration. The model is validated against experimental observations for gel times of 32 minutes to 766 minutes, the model accurately predicts the log(gel time) with an average error of 4{\%} which corresponds to an R2 value of 0.96 The model is then applied to a hypothetical case study to demonstrate its use in grout design, based on published in-situ groundwater data from the Olkiluoto area of Finland. The model successfully predicts the required accelerator concentration to achieve a grout gel time of approximately 50 minutes, taking into account the cations already present within the synthetic groundwater.",
keywords = "colloidal silica, grouting, injection, groundwater chemistry, viscosity, gel time",
author = "M. Pedrotti and C. Wong and {El Mountassir}, G. and Lunn, {R. J.}",
year = "2017",
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TY - JOUR

T1 - An analytical model for the control of silica grout penetration in natural groundwater systems

AU - Pedrotti, M.

AU - Wong, C.

AU - El Mountassir, G.

AU - Lunn, R. J.

PY - 2017/11/30

Y1 - 2017/11/30

N2 - Over the last three decades, colloidal silica has been investigated and more recently adopted as a low viscosity grouting technology (e.g. for grouting rock fractures within geological disposal facilities nuclear waste). The potential of colloidal silica as a favourable grouting material exists due to: its initial low viscosity; its low hydraulic conductivity after gelling (of the order of 10-7 cm/s); the very low injection pressures required; its controllable set/gel times (from minutes to several days); the fact it is environmentally inert; its small particle size (less than hundreds of nanometres) and its cost-effectiveness. Despite the documented success of colloidal silica based grouts for hydraulic barrier formation, research has not translated into widespread industrial use. A key factor in this limited commercial uptake is the lack of a predictive model for grout gelling which controls grout penetration: whilst data are available to underpin design of a grouting campaign in laboratory conditions, little research has been done to underpin applications in natural environments. Here we develop and validate an analytical model of colloidal silica gelling in groundwaters with varying pH and background electrolyte concentrations. This paper presents an analytical model that accounts for changes in pH, electrolyte concentration, cation valency and molar mass, silica particle size and silica concentration giving predictive capability without the need for site-specific calibration. The model is validated against experimental observations for gel times of 32 minutes to 766 minutes, the model accurately predicts the log(gel time) with an average error of 4% which corresponds to an R2 value of 0.96 The model is then applied to a hypothetical case study to demonstrate its use in grout design, based on published in-situ groundwater data from the Olkiluoto area of Finland. The model successfully predicts the required accelerator concentration to achieve a grout gel time of approximately 50 minutes, taking into account the cations already present within the synthetic groundwater.

AB - Over the last three decades, colloidal silica has been investigated and more recently adopted as a low viscosity grouting technology (e.g. for grouting rock fractures within geological disposal facilities nuclear waste). The potential of colloidal silica as a favourable grouting material exists due to: its initial low viscosity; its low hydraulic conductivity after gelling (of the order of 10-7 cm/s); the very low injection pressures required; its controllable set/gel times (from minutes to several days); the fact it is environmentally inert; its small particle size (less than hundreds of nanometres) and its cost-effectiveness. Despite the documented success of colloidal silica based grouts for hydraulic barrier formation, research has not translated into widespread industrial use. A key factor in this limited commercial uptake is the lack of a predictive model for grout gelling which controls grout penetration: whilst data are available to underpin design of a grouting campaign in laboratory conditions, little research has been done to underpin applications in natural environments. Here we develop and validate an analytical model of colloidal silica gelling in groundwaters with varying pH and background electrolyte concentrations. This paper presents an analytical model that accounts for changes in pH, electrolyte concentration, cation valency and molar mass, silica particle size and silica concentration giving predictive capability without the need for site-specific calibration. The model is validated against experimental observations for gel times of 32 minutes to 766 minutes, the model accurately predicts the log(gel time) with an average error of 4% which corresponds to an R2 value of 0.96 The model is then applied to a hypothetical case study to demonstrate its use in grout design, based on published in-situ groundwater data from the Olkiluoto area of Finland. The model successfully predicts the required accelerator concentration to achieve a grout gel time of approximately 50 minutes, taking into account the cations already present within the synthetic groundwater.

KW - colloidal silica

KW - grouting

KW - injection

KW - groundwater chemistry

KW - viscosity

KW - gel time

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DO - 10.1016/j.tust.2017.06.023

M3 - Article

VL - 70

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EP - 113

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T2 - Tunnelling and Underground Space Technology

JF - Tunnelling and Underground Space Technology

SN - 0886-7798

ER -