Influence of Lime on the Undrained Shear Strength of Water Treatment Sludge from Cubatao: Miniature Vane and Fall-Cone Tests

Abstract

Even after dewatering, WTS water content (w) is very high and undrained shear strength (Su) is very low. Lime is used to decrease plasticity and enhance workability and shear strength of soft soils. WTS stabilized with lime may be a suitable material as covers of sanitary landfills, filling of trenches, pavement subbases and other geotechnical applications. This paper presents the influence of lime on Su of WTS-lime mixtures at lime contents of 5, 10, 25, 50, 75, 100 and 150% (dry weight basis). Also, determination of Hansbo's cone factor (K) for WTS-lime mixtures by calibration with miniature vane data was performed, obtaining K of 1.27. Miniature vane and fall-cone tests indicated that Su smoothly increases with lime content from 1.0 to 2.3 kPa and from 0.9 to 3.0 kPa, respectively, which were lower than expected. Su presented high dispersion for both vane and cone tests, and only a subtle increase of Su was observed for the increase of consistency index from -1.50 to 0.07. In conclusion, vane and cone tests are not adequate to measure Su of WTS-lime mixtures with precision, and a proportion of WTS:lime higher than 2:1 (150%) is necessary to transform WTS in a geo-material.