Groundwater flow below construction pits and erosion of temporary horizontal layers of silicate grouting
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PAPER
Groundwater flow below construction pits and erosion of temporary horizontal layers of silicate grouting Joris M. Dekker 1 & Thomas Sweijen 1,2 & Alraune Zech 1 Received: 24 April 2020 / Accepted: 17 September 2020 # The Author(s) 2020
Abstract Injection of silicate grouting materials is widely used to create temporary horizontal layers for reducing inflow of groundwater at construction sites, in regions with shallow water tables. The erosion of a grouting layer was investigated by means of analytical solutions for groundwater flow and transport within a pit after construction finished. Erosion is assumed to occur by dissolution of the temporary injection layer and subsequent advective transport. Thereby, the hydraulic conductivity changes with time. This paper presents novel analytical solutions and approximate solutions for the major fluxes in the construction pit as a function of the domain settings, aquifer gradient and hydraulic conductivity. In addition, the mass flux and the dilution ratio of erosion-related components leaving the construction pit and entering the aquifer are quantified. Derived solutions are verified against numerical simulations. A sensitivity study shows the impact of domain settings on fluxes and dilution ratio. The results confirm that mass flux of grout components increases with ongoing erosion. Thus, its effect on groundwater quality increases with time after construction ceased. Keywords Silicate grouting . Erosion . Flow barriers . Analytical solutions . Contamination
Introduction Over the last decades, urbanization resulted in an increasing demand in space for infrastructure within already densely populated areas. Therefore, many infrastructures are developed within the subsurface such as drainage systems, underground public transport networks, roads and parking facilities. Realizing these structures often require working below the water table. This requires sealing and dewatering of excavation sites, whilst keeping the impact on the surrounding aquifer to a minimum. A well-established method to build an excavation site in urban areas of shallow-groundwater is by combining vertical Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10040-020-02246-3) contains supplementary material, which is available to authorized users. * Thomas Sweijen [email protected] 1
Department of Earth Sciences, Environmental Hydrogeology Group, Utrecht University, Princetonlaan 8a, 3584CB Utrecht, The Netherlands
2
Crux Engineering BV, Amsterdam, The Netherlands
soil-retaining walls and lowering the water table by pumping within these walls (Azzam 2004, Powers et al. 2007; Pujades et al. 2014). However, large-scale dewatering activities lower the water table beyond the excavation site, having negative environmental impact—for example, pumping induced drawdowns (in the order of meters) cause settlement of the soil (e.g. Spacagna et al. 2017) or displacement of contaminants which are often present in urban aquifers (Fetter et al. 2018). Moreover, shallo
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