Lessons learned for ground movements and soil stabilization from the Boston Central Artery

This paper summarizes lessons learned about soil stabilization with the deep mixing method (DMM) as it was developed and applied over 10 years during construction of the Boston Central Artery and Tunnel (CA/T). It also summarizes lessons about the control of excavation-induced ground movements and their characteristics. Deep deposits of marine clay were stabilized with DMM for large open cuts at Bird Island Flats and Fort Point. Channel, both of which are described with respect to site conditions, soil properties, DMM installation and characteristics, and measured field performance. Topics addressed in this paper include water pressure distribution behind DMM walls, statistical characterization of soil cement properties, quality control/quality assurance procedures, comparison of measured and numerically simulated deformation in clay stabilized with various configurations of soil cement elements, shear modulus degradation characteristics of in situ soil cement, and ground movement patterns. Recommendations are made for soil cement properties, installation procedures, analytical modeling, design, and inspection.