Geotechnical parameters of loess-cement mixture for construction of compacted soil-cement cushion

Soil-cement cushions are compacted and stabilized layers of the soil base, built under the foundation. Usually, they are constructed with local soil from the excavation, mixed with Portland cement. In Bulgaria, this soil improvement technique has been applied in foundation works in collapsible loess ground, aiming to replace a part of the collapsible layer, to increase the bearing capacity of the soil base, and/or to play a role of engineering barrier against migration of harmful substances in the geoenvironment. A multi-barrier near-surface short-lived low- and intermediate-level radioactive waste repository is under construction in Bulgaria. A loess-cement cushion beneath repository cells is going to be built by in-situ compacted mixture of local loess and Portland cement. Based on the results from classification and physico-mechanical tests of a set of loess-cement mixtures, it was proposed optimum cement content of the loess-cement cushion beneath the radioactive waste repository to be 5% of Portland cement. The present paper aims to assess the following geotechnical parameters of the selected loess-cement mixture after proper curing: unconfined compressive and flexural strength; shear strength parameters; static and dynamic elastic constants; and hydraulic conductivity. The results obtained prove that the mixture prepared at W_opt and ρ_ds of local loess and 5% (by the dry weight of soil) of Portland cement type CEM I 42.5 N – SR 5 possesses strength and deformation characteristics that completely meet the design stress-strain requirements to the soil-cement cushion beneath the repository foundation.