Construction) using its proprietary “Turbo Mix” system. Over 17,000 soilcrete elements were installed employing over 380,000 tonnes (417,000 tons) of slag- cement in a period of about 13 months. Given the intense pressure on schedule, the USACE employed the ECI (Early Contractor Involvement) concept whereby the successful contractor was selected on a 10% design basis. This project remains by far the largest DMM application in the U.S., and one of the largest in the world. It set new standards in productivity and quality in North American Deep Mixing practice. New Arrivals All of the numerous vertical axis DMM techniques may be referred to as “conven- tional.” As shown in Figure 1, these have now been supplemented by two other groups of techniques, broadly classified as “Horizontal Axis Cutting and Mixing,” and “Vertical Continuous Trenching.” The former is most commonly represented by the CSM (Cutter Soil Mix) method, devel- oped jointly between Bauer Maschinen of Germany and Bachy Soletanche of France in 2003. By 2011, over 150 projects were completed worldwide, mainly with Bauer’s newly patented CSM, with a significant number in North America. CSM is an evolution of earlier trench cutter (hydro- mill) technology, whereby grout is injected via the cutter as it is advanced and wi thdrawn, to create individual rectangular-shaped soilcrete panels. undertaken since 2006. In all the applica- tions, the quality of the Deep Mixing, in terms of the homogeneity, strength and permea- bility of the soilcrete, has been exceptional. Deep Mixing by Vertical Continuous Trenching is represented solely by the TRD (Trench Cutting Remixing Deep Wall) Method. This is a 1993 Japanese development introduced to the U.S. by Hayward Baker in 2006. It uses a full- depth, vertical “cutter-post” with a peripheral cutting chain. As this vertical tool is drawn through the ground, the crawler-mounted chainsaw cuts and mixes the soil with grout (injected from ports on the post). It provides a continuous wall, without joints, with a very high efficiency of vertical mixing. Widths of 560 to 840 mm (22 to 33 in) and depths to 55 m (180 ft) are feasible, in appropriate conditions, i.e., those that are “rippable.” TRD has been used on several U.S. projects to date, by far the largest being, as for CSM, at Herbert Hoover Dike, Fla., for constructing miles of cut-off wall. Studies, Researches and Conferences Figure 1. Classification of DMM technologies The largest CSM project in the U.S. is the construction, by Bauer, of several miles of 600 mm (24 in) wide cut-off, to depths of over 20 m (65 ft) in Herbert Hoover Dike, Fla. In Canada, the current work being conducted by Golder Construction for foundation improvement at Kitimat, B.C., is the most impressive of the many projects Deep mixing expertise has experienced sub- stantial growth and dispersion in the U.S. over the past two decades through a combination of contractor innovations, design creativity, research endeavours, and several notable publications and conferences, as well as numerous semi- nars and short courses. Deep mixing contractors continually improve their tooling and their binder delivery and mixing processes to enhance mixture quality and productivity. Such innovations include adding stationary blades to single axis mixing equipment and delivering slurry under pressure through nozzles located along the arms of mixing blades. Contractors and researchers have dev- eloped a greater understanding of the ways that different binders and mixture proportions influence compressive strength, shear strength, tensile strength, ductility, and stiffness of different inorganic and organic soils; although more work remains to be done in this area. Designers and researchers in the U.S. have developed improved analysis techniques to permit efficient design against multiple failure modes and to successfully integrate design, construction and QC/QA to reliably account for variability in property values. Important progress has been made in design to resist seismic loading and mitigate liquefaction, although again more work remains in this area. Significant practice-oriented research in the U.S. was funded in the early 2000s by the National Deep Mixing Program, a collaborative effort among the FHWA and ten state DOTs, and by separate initiatives by FHWA and state DOTs. The U.S. Army Corps of Engineers sponsored the test program in New Orleans described previously, as well as development of simplified analysis and design procedures that capture important features of deep mixing foundation systems for levees and floodwalls in soft ground. The USACE design procedures formed the basis for a design manual prepared for FHWA for DEEP FOUNDATIONS • NOV/DEC 2013 • 55
