Geotechnical properties of lime stabilised loess, Port Hills, Canterbury.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The loess deposits of the Port Hills, Canterbury, are subject to erosion by natural processes. Urban development of the Port Hills has encountered difficulties due to loess erosion, and in some instances, contributed to erosion. Lime stabilisation is one remedial method that can be used to reduce erosion problems. This necessitates investigation of the changes to soil properties and strength gains that occur to the loess with the addition of lime. An erodible loess colluvium, from a subdivision with a history of erosion problems, was stabilised with 1%, 2.5%, 5%, 7.5%, and 10% hydrated lime, and cured under various laboratory conditions. Pinhole erodibility, uniaxial swelling strain, Atterberg limits, grainsize analysis, Proctor compaction testing and a slaking test were used to determine the improvements to soil properties with the addition of lime. Unconfined compressive strength was tested to determine strength gains of lime stabilised soil. The addition of 1% lime to the soil produced a non-erodible, non-dispersive material. Slaking and swelling were minimised with the addition of higher percent ages of lime (5%-7.5% respectively). The effective grainsize of the soil was increased on the addition of lime, and plasticity was increased with the addition of up to 5% lime. Optimum moisture content increases, and dry density decreases with increasing amounts of lime. Strength gains of the lime stabilised loess, varied from 3 – 14 times the strength of the untreated soil depending on the curing method. Strength gains were greatest for air dried samples, although the untreated soil cured in the same manner had a higher dry strength than the lime stabilised soil. Strength gains are optimised at and above 7.5% lime with significant strength losses recorded between 2% and 5% lime. Strain deformation is reduced with the addition of lime, and the modulus of deformation is increased significantly indicating that lime stabilised loess acts as a brittle material on deformation. The addition of lime to loess in low percentages (1%), has the effect of producing a non-erodible, non-dispersive material that resists erosion. However, it would appear that to achieve maximum strength of lime stabilised loess, 7.5% lime or more must be added to the soil.