Small-scale laboratory test on expansive soil stabilized by CCR-Fly ash columns

Volumetric changes in expansive soils due to seasonal moisture changes can seriously damage foundations. In the small-scale laboratory study reported in this paper, the effect of inserting columns made from calcium carbide residue (CCR) and fly ash (FA) to reduce the swelling potential of expansive soil was examined. An attempt was made to determine the mineralogical changes in the soil and to identify newly generated reaction products by X-ray diffraction (XRD). The strength gain of the stabilised soil was investigated using unconfined compressive strength tests. It was found that the heave of the soil with columns of CCR and FA installed by in situ mixing and compaction reduced by up to 88% and 57%, respectively. The compressive strength of samples increased up to two-fold, and around the same level, for both installation methods after 90 d of curing. This increase in strength was an outcome of soil modification and stabilisation. The XRD results indicated the change in soil mineralogy. Further studies are required to study the cyclic swell–shrink behaviour of the stabilised expansive soil.