CS19B - Concurrent Session 19B: Long Term Strength Gain of Soil Cement Bentonite Mixtures and Current States of Practice

Abstract Description: This paper has been written to document the long-term strength gain of soil cement bentonite (SCB) mixtures used to construct seepage barriers in dams/levees as well for structural components for embankment stability and/or seismic remediation projects. While current state of practice uses technical specifications aligned with concrete industry standards (i.e., the American Concrete Institute) in terms of strength measurements, SCB mixtures can exhibit long-term strength gains far exceeding design specification requirements. For the presented case study herein, long-term strength testing from SCB mixtures installed in a seepage cutoff wall has shown significant strength gains on the order of 500% at 180 days to 365+ days post-mixing as compared to 28-day unconfined compressive strength (UCS) results, commonly the strength specified in construction specifications. Strength and permeability results from field samples collected during construction suggest soil type, cement content, fines content, and mineralogy, among other factors can play a significant part in the final engineering properties of the SCB mixture. The results from this case study, including limited results from other similar projects, suggest that traditional concrete testing specifications may not be applicable to specify the design strength or other properties of a SCB mixture in the field. This case study provides long-term strength testing results from an SCB wall constructed with variable foundation conditions and design cement contents. Results of this case study should be considered for future projects based on design intent and deep soil mixing (DSM) strength necessity.