A case history of shallow sloughing within cut slopes of an irrigation canal in salt-rich clayey colluvium

An investigation and remediation of instability along cut slopes of an irri gation canal in salt-rich clayey colluvium in southern Alberta is described . Random sloughing of the canal side slopes began to occur 2 years after co nstruction over a 7500 m length of canal and was nearly continuous over a 2 500 m length 3 years later. The sloughs are shallow seated and most had the appearance of a "mud" flow. Soil salinity also developed along the canal s lopes due to capillarity and evaporation. Failure of the clay slopes in the cut sections is attributed to swelling, dispersion, and softening of the s ubgrade due to exposure of the salt-laden clays to fresh water. In contrast , 600 m of salt-rich clayey colluvium compacted as a clay liner on the cana l side slopes showed no evidence of sloughing and salt loading after 9 year s of service. Good soil compaction inhibited softening and slope instabilit y in these salt-rich soils. Results from detailed site investigations and o bservations, and the interplay of soil chemistry and geology, facilitated t he selection of a satisfactory method of repair. Repairs consisted of recon structing 2500 m of canal by overexcavating the canal subgrade and replacin g those soils with compacted soil.