ABSTRACT
Sub-slab Depressurization (SSD) aims to reduce building occupants’ exposure to toxic gases from the soil. These gases can either be generated from contaminated soils (like Volatile Organic Compounds or Landfill Gas) or naturally present in the soil (like Radon). The SSD system is composed from the bottom to the top of a separator geotextile, a drainage layer, and a vapor barrier. One or more gas pits are located according to the gas concentration in the area and to the geometry of the building. Because most of the SSD systems are constructed in high-density population areas (e.g., new construction in old industrial zones), the truck traffic and the noise resulting from the excavation works, and the transportation of granular material is a nuisance for residents. It also damages the local road network that is not designed to handle heavy vehicles traffic. This paper presents the sizing and the use of multi-linear drainage geocomposite as part of the SSD system providing separation and gas collection functions. The geocomposite is composed of non-woven geotextile layers incorporating perforated mini-pipes regularly spaced and running the roll length. It is connected to a collector pipe and to the gas pit. It collects the soil gas and reduces the head losses thanks to the high-density network of perforated mini-pipes within the product and the specific fittings used to connect the product to the main collector pipe. The sizing of the geocomposite is done using laboratory tests and software to characterize the flow capacity and the head losses of the system. Multi-linear drainage geocomposites have been found to be efficient for both passive and active SSD systems.
