Frost-Protected Shallow Foundations in Cold Climates

Guy L. Titley

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Cold Regions II

ABSTRACT: In cold climates, foundation walls and footings should be located below frost depth to prevent frost damage. Frost-protected shallow foundations (FPSF) using specific thicknesses of extruded polystyrene insulation in strategic configurations can allow much shallower installation of foundation walls/footings while still protecting the foundations from frost effects. A proper design can provide long-term building performance, improved construction scheduling advantages and construction cost savings compared to conventional full-depth foundation. The building science and engineering principles behind FPSFs, Building Code acceptance of the concept and the proper insulation value/placement for FPSF in -Protected Shallow proper selection of insulation type required for this building insulation with long-term soil contact are important factors for building sustainability. This as well as comparative cost data and advantages/disadvantages

RÉSUMÉ: Dans les climats froids les murs et semelles de fondation doivent être situés sous la profondeur du gel pour prévenir les dommages duudé aux endroits stratégiques de la fondation un système de fondations isolées peu profondes (FPSF) permet une installation moins profonde tout en protégeant les fondations des éffets du gel. Une conception convenable fourni une performance à long-terme, une séquence de construction améliorée est des couts de constructions réduits comparativement aux fondations acceptations du concept par les Codes du Bâtiment, et le choix de valeur isolante et de son emplacement selon ASCE t-Protected Shallow Foundations seront élaborés. pour une telle application ou la performance en contact à long-terme avec le sol humide et facteurs affectant la durabilité de la fondation sera présentée. Ceci et des renseignements de couts de construction comparatifs et des avantages/désavantages du concept seront partagés. In cold climates the protection of foundations walls, footings and slabs on grade is necessary to prevent potential damage from frost effect. Combinations of climate severity, building interior temperature and soil type can permit the frost line to reach the face of the foundation walls and in a worse condition as far as under the footings. The presence of a frost-susceptible soil exacerbates the problem. Soil frozen to the outer face of a foundation wall can result in upward ad-freezing shear forces as high as 70 to 100 kPa (Penner et al. 1971). If the frost susceptible soil is also located under the footings frost heave can also occur. The conventional practice to reduce the effects of frost penetration is to locate the footing below the expected frost depth. Depending on the climate severity as measured by the Air Freezing Index (AFI) and the soil type and cover frost can penetrate up to 4 meters deep at the exterior face of foundation walls. This makes excavation and construction potentially very difficult and expensive. The frost-protected shallow foundation (FPSF) is a proven construction method for frost protection and does not require extending the wall below local frost depth. A FPSF can be constructed with a footing as shallow as 0.3 m below finished grade (Fig 1). Figure 1 Conventional versus FPSF (SEI/ASCE 32-01), FPSFs are not a new building technology. It originated in Scandinavia where it was researched as a method to provide frost protection and cost savings for residential construction. The first research started in Sweden and Norway in the 1950s (Farouki, 1992). The FPSF method for construction had about 50,000 slab-on-grade foundations built by 1972 (Togerson). Research conducted by the Swedes led them to better define insulation requirements and its location and effects of

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