Investigation of gas flow through soils and granular fill materials for the optimisation of radon soil depressurisation systems

Abstract

The purpose of this study is to investigate gas flow through different types of granular fill materials and soil by means of a series of experimental laboratory tests, in relation to soil depressurisation systems for radon reduction under buildings and the soil surrounding the foundation. Air permeability characterisation of materials used as granular fill material layer beneath the slab in buildings is a key parameter for optimum performance of soil depressurisation systems to mitigate radon. A test apparatus was developed, adapted from previous studies, to measure the gas permeability of the samples and Finite Element Method numerical simulations were validated to simulate the flow behaviour through them. Theoretical expressions for permeability were discussed based on the analysis of experimental results and numerical simulations, finding that Darcy-Forchheimer equation provides the best match to the experimental results. Darcy's law also proved to be suitable for low gas velocities, whereas Ergun's equation resulted in a poor fit of the experimental data. Benchmark analysis of the granular fill materials under study and other European standards (Spanish, Irish, British) are also presented.

A full-scale experimental study of sub-slab pressure fields induced by underground perforated pipes as a soil depressurisation technique in radon mitigation

“…As expected, the values were distributed more uniformly in the gravel than in the soil. As the permeability levels recorded in the gravel were higher than the upper limit of the Radon-JOK range, however, additional laboratory tests were conducted to standard ASTM D6539 (ASTM International, 2013;Fuente et al, 2019a). The mean values found were: Gravel: K (9.0 ± 3.5) × 10 −8 m 2 Soil: K = (4 ± 2) x10 -12 m 2 which lay within the range usually reported for the type of substrates at issue (Neznal et al, 2004)…”

“…In the initial lengths the effect is reinforced by the greater pressure drop associated with the turbulence induced by greater air speed. That development was studied by factoring the Forchheimer equation into Darcy's law (Fuente et al, 2019a):…”

“…The presence of negative pressure fields is favoured by more permeable sub-slab fill material such as gravel and hindered by compact natural soil (Diallo et al, 2018;Fuente et al, 2019a;Gadgil et al, 1991;Hung et al, 2019Hung et al, , 2018a. Pressure field constraint has also been observed when a slab fails to ensure impermeability between the soil and the indoor space (EPA Environmental Protection Agency., 1994;Frutos and Muñoz, 2018).…”

A Multisensor System for the Characterization of the Field Pressure in Terrain. Accuracy, Response, and Adjustments

“…In order to form relationships between pressure transmission and soil permeability, the data were compared with a laboratory experiment. PressureNet system was applied to a test apparatus filled with different granular fill material types [15]. Material types included natural soil from the experimental slab place and the gravel 4/20 used under slab.…”

Follow-up study on indoor radon levels in Irish schools after a National School Survey and remediation programme

“…Recognised as the second leading cause of lung cancer by the World Health Organisation (WHO), indoor exposure to radon gas is responsible for around 300 lung cancer cases per year in Ireland (1,2). To minimise indoor radon concentrations, there are various prevention and remediation techniques, often these remediation techniques are dependent on the gas flow through the granular fill materials used in the building construction (3)(4)(5)(6)(7). Measuring radon concentrations is key to controlling radon levels in any type of building (8,9).…”