Characterization of consolidation and creep properties of Salt Lake City clays

Abstract

The reconstruction of the Interstate 1-15 highway embankments in Salt Lake City (SLC) involves the design and construction of bridges and embankments over 20 - 30 m of soft SLC clays. A surcharging scheme to overconsolidate the soft, layered foundation soils is required to reduce post-construction creep settlements. Seven Constant Rate of Strain Consolidation (CRSC), nine special Type B (surcharge) oedometer, two special Type C (reload) oedometer, 16 Ko-Consolidated phase of direct simple shear SHANSEP and six Ko-Consolidated phase of triaxial SHANSEP tests were run on radiographed tube samples to evaluate the consolidation and creep properties of the SLC clays. Comparison between the end-of-primary (EOP) compression curves from continuous loading and those from incremental loading shows that continuous loading gives higher values of the maximum virgin compression ratio (CRmax), especially for S-shaped compression curves on high water content clays. Continuous loading also provides more reliable estimates of preconsolidation stress ([sigma]'p). Data from 19 oedometer tests show that Ca/CR increases with increasing natural water content and has a mean value of about 0.042. The thesis presents correlations for predicting the reduction in creep rate of SLC clays as a function of the amount of surcharge (AOS). These correlations show greater benefit from surcharging than reported by Ladd (1989) for other cohesive soils. The thesis also contains correlations for predicting the long-term settlements of SLC foundation clays that are overconsolidated due to aging from prior embankment construction.