Recommendations for the proposed alignment of the new bridge were made in 1999. The selected alignment places the new bridge north of the existing Martin Luther King Bridge and south of the existing McKinley Bridge. The Illinois and Missouri Departments of Transportation (IDOT and MODOT, respectively) separated the bridge, approach ramps and highway relocations into seven individual projects, excluding the land-based approach ramps on the Missouri side of the river. Geotechnology Inc., St. Louis, was selected to provide drilling services on six of the seven projects and laboratory testing and engineering services on three of the projects.
To date, the projects have included the installation of over 800 geotechnical borings for the foundation design of various facets of this significant group of projects, having an estimated construction cost of more than $1 billion. Construction could begin in 2004 if funding is available, and when completed, the new Mississippi River Bridge will be the widest cable-stayed bridge in the world (222 feet) and the longest in the Western Hemisphere (2,000-foot main span).
Two of the projects (the new bridge and the relocation of Interstate 70) presented distinct but related problems regarding the installation of overwater borings. Geotechnology Inc. contacted Shallow Draft Elevating Boats Inc. of St. Bernard, La., to assist in developing a work plan to accomplish both projects in a single mobilization.
The Shallow Draft Elevating Boat Model 35/15 proved to be the ideal craft to work in the shallow lake waters. The self-propelled barge was mobilized from its Louisiana base in a single tractor trailer load, assembled and launched from a temporary access ramp along the west bank of the lake using a portable crane. Even when loaded with a trailer-mounted CME 45 drill rig, tools and crew, the SDEBI 35/15 easily maneuvered across the lake. Once in place, the hydraulically operated jacks raised the barge quickly, providing a safe and stable platform from which to perform the drilling and sampling operations.
As a result of the use of the SD 35/15 barge, Geotechnology Inc. was able to complete a challenging task while reducing estimated barge costs for the projects by approximately $50,000, when compared to conventional methods. In addition, the portability and flexibility of the SD 35/15 enabled Geotechnology's crews to accomplish two over-water projects in vastly different environments quickly and safely.