Deep Dry Soil Mixing – Performance And Quality Control Acceptance Criteria

The variability in strength and compressibility of in situ deep soil mixing (DSM) of soft soils can be greater than the variability of the natural soil. To achieve economy, sustainability and performance of DSM, it is essential that construction be carried out using an appropriate QA/QC program.

This paper presents the results on the use of DSM columns to support several embankments over soft clay in the Ballina Bypass and Pimlico to Teven Pacific Highway projects. The DSM work was carried out under the Roads and Maritime Services (RMS) Specification, with QA/QC testing procedures developed specifically for these projects. Embankments with contrasting performance are compared to the quality control test results which comprised laboratory testing of core samples as well as in situ test results such as pull-out and push-in vanes and conventional cone penetration tests. Settlement monitoring indicated that where the acceptance criteria are met measured settlements under embankment loading were generally less than predicted settlements. The observed settlement in an area with high organic content was twice the predicted value, although in all cases, post-construction settlement met the performance objectives.

Based on these results, recommendations on QA/QC testing procedures are made with the aim of improving economical and sustainable construction of the DSM ground improvement technique for soft soils.