Abstract:
The success of deep soil mixing to mitigate risks associated with problematic soil conditions has led to an increased acceptance and utilization of mixing technologies in challenging geologic conditions throughout North America. A key factor of successful deep mixing projects is a robust quality control program, consisting of both laboratory and field verification testing, to identify highly plastic cohesive soils and/or organics that would negatively impact the soil-cement quality. A pre-mobilization laboratory program allows practitioners to test the mixability and hydration of the designed grout slurry with the soils and provides insight into how the in-situ soil characteristics will influence the final soilcement properties. In variable soil profiles the laboratory program can be used to develop site specific correlations between soil characteristics and the soil-cement properties to assist in developing targeted grout dosage rates and/or mixing parameters for highly plastic clays and/or organic zones. The field verification testing program will ultimately be used to validate the grout design and confirm the mixing program is adequate to properly disaggregate, blend, and stabilize the soils. In many cases, the continuous review of field verification results allows the project team to modify the grout slurry and/or adjust mixing parameters due to better soil-cement quality as compared to laboratory prepared samples. This paper provides a review of single-axis deep soil mixing case histories highlighting the impact of highly plastic cohesive soils and organics on the soil-cement mixture quality and provide some observed correlations and disparities between laboratory results and field verification data. The results will reinforce the importance of laboratory testing to initially characterize problematic soils, but ultimately demonstrate that field verification testing, along with experience in similar soil conditions, is required when developing a deep soil mixing program. Keywords: Soil Mixing, High Plasticity, Cohesive, Organics, Strength