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

Sub-slab depressurisation systems have proven to effectively mitigate radon entry. A poor understanding of the fluid physics underlying the technique has been shown to lower the success rate substantially. This article describes a study of pressure fields in a sub-slab gravel bed induced by a soil depressurisation system consisting of perforated pipes run under the slab at a depth of 75 cm. The advantage of the approach is that pipes can be laid from outside the building to be protected. The study was conducted on a large-scale experimental facility where the variations in morphology and scope of pressure fields with different pipe combinations could be monitored and characterised. The findings showed that pressure was uniform across the entire area in the gravel bed, whereas the sensors buried in natural soil showed pressure to depend on distance from the source. Pressure transfer to the sub-slab plane was also observed to vary depending on the active pipe. Air-flow resistance studies in the layers of soil lying between the pipes and the gravel delivered different results for each pipe. That finding would appear to be related to the presence of preferential pathways in some parts of the soil. Total pressure when several pipes were activated was observed to be practically the same as the sum of the pressures transferred by each when working separately. The correlation between extraction fan power and pressure generated was also analysed. These and other factors are discussed and analysed from a perspective of the understanding of such highly effective techniques.

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

In different disciplines of science, the knowledge of the resulting pressures in the subsoil can help to understand physical phenomena of mass exchange between the atmosphere and the terrain. The measurement of lower differential pressures is complicated given the low range of detected values. In this paper, a multisensor system has been designed and developed to measure differential pressures in radon gas transport studies. The adequacy of this system has been proven using a purpose-built pressure chamber and an automatic motion system developed by the authors. The temporal response frequencies, the pressure values measured by the sensors, and their ability to link in series were analyzed to offer a multisensor spatial and temporal mapping. At the same time, the influence of the components required for a real deployment were studied using different tube lengths and diameters, connectors, and obstructions across the operating range of the pressure sensors. The system has also been tested for measuring differential pressures in a real model with a concrete slab above the soil and a pressure generator system below. It was found that this system is very suitable for outdoor measurements that demand a quick temporal response and accuracy.

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

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. Gas permeability characterisation of materials used as granular fill material beneath the slab in buildings is a key parameter for the 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 and British) is also presented.