ABSTRACT
Over the past 5 years, a major research programme has been carried out into the use of lime/ggbs for the stabilisation of soils. This paper reports on selected parts of that programme, which relate to the oxidation of pyrite (iron sulfide), and the potential expansive effect that oxidation of sulfide can produce in stabilised clays. Field and laboratory studies on stabilised pyrite-containing clay, detected considerable oxidation of sulfide to sulfate and this was accompanied by expansion. The use of ggbs was beneficial in combating the expansion. Although oxidation of sulfides in soils is normally slow, the rate was found to greatly increase with the elevation of pH that is produced by addition of lime or cement. It is concluded that the physical and chemical effects that are an inherent part of soil stabilisation (i.e. disturbance of the soil, and most importantly, the elevated pH) produce conditions very conducive to the oxidation of sulfides. Consequently it is recommended that, when assessing the suitability of soils for stabilisation, the sulfide content as well as the sulfate content should be measured and it should be assumed that the sulfide is available for conversion to sulfate.
