REASONING ON IMPLEMENTATION OF FROST PROTECTED SHALLOW FOUNDATIONS

Abstract

Implementation of frost protected shallow foundations (with insulation) in frost susceptible soils in the areas of the Baltic region is an item under discussion. A design method recommended by EN ISO 13793 has been applied. The design base is the EN 1997-1 which includes conditions and valid climatic data for the localities in the Republic of Latvia. The study contains the results of external air temperature data processing from the last 70 years, and consequently a determination of a freezing index value, and moreover pointing out the variation depending on the reference period taken. Results of temperature data processing for decades of winter seasons testify that quite distinctive frost protection levels may be defined for shallow foundation design parameters depending on the number of frost seasons sampled. The specific design results were obtained for eccentrically loaded columnar spread foundations of an unheated building insulated to reduce heat loss from the soil below the foundations keeping the subgrade soil unfrozen. As a result of the research the conclusion about the benefits expected has been presented, based on the comparison of concrete consumption and soil excavation volumes from different localities in Latvia. It has been concluded that the cost effectiveness of heated foundations correlates closely with the type of frost-heaving soil. Use of frost protected shallow foundations in clayey soils leads to an increase of ground volume to be excavated and filled back, and concrete consumption for foundations decreases. In silty sand soils, if the required foundation depth is less than some definite level, both reductions may be achieved by shifting the ground, and in concrete consumption as well.