DMM Implementation Challenges at the Glen Road Interchange: Lessons Learned

The Minnesota Department of Transportation (Mn/DOT) embarked on their first use of Deep Mixing Methods (DMM) in the fall of 2002. The technology, while not new to the United States, was new to Mn/DOT and the implementation required a considerable amount of additional oversight and attention. The deep mixing (DM) work was to consist of approximately 60,000 m³ of treated ground as part of a $45M project involving three bridges, six approach ramps, roadway reconstruction and associated grading, paving, signing, and signals. Unusual to most Mn/DOT projects, geotechnical engineers were involved through both design and construction of the foundation work; involvement ranged from providing the original design concept and development of the plans, special provisions, and QA/QC (Quality Assurance/Quality Control) program, to the consideration of contractor value engineering (VE) proposals, assessment of sampling and coring of specimens, and assisting in the resolution of construction issues involving a problematic site strata with cobbles and boulders. Designing and preparing the necessary specifications and contract documents took more effort than originally predicted. In addition, despite careful attention to detail, there were two significant areas in the special provisions where confusion occurred: definition of pay items and the monitoring/instrumentation program.