By using a self-propelled barge, a St. Louis company was able to overcome some challenging tasks when performing work for this new bridge.

For decades, a major transportation need in the St. Louis metropolitan region has been a new bridge crossing the Mississippi River in the downtown St. Louis area. Much of the recent growth of the region has occurred in the Illinois counties adjoining St. Louis, resulting in heavy vehicle traffic crossing the existing downtown bridges on a daily basis. However, the number of traffic lanes crossing the Mississippi River at St. Louis has dropped from 22, in 1965, to a current level of 16.

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.

Under contract with the Chicago office of H. W. Lochner Inc., Geotechnology Inc. provided drilling, laboratory and geotechnical engineering services related to the design aspects of approximately 2 miles of new interstate highway linking the existing I-70 to the new bridge. Approximately 1,500 lineal feet of the new highway will traverse an existing small lake; therefore, a number of deep and shallow borings required a floating platform to accommodate the drilling equipment because the small lake is shallow (ranging in depth from 2 feet to 5 feet) and there were no facilities from which to launch a floating drilling platform.

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.

Concurrent with the onset of work in the lake, final boring locations for the main pylons of the new bridge were established by the prime bridge designer, Modjeski & Masters Inc. The final boring plan required that three of the six borings for the Missouri Pylon be installed along the west bank of the Mississippi River in North St. Louis. The over-water borings were located between the west bank and an existing barge-loading facility. The limited space, water currents and constant water level changes prohibited the use of conventional spud barges and towboats. Again, Geotechnology Inc. relied on the shallow draft SD 35/15 self-propelled barge to get the job done. The barge was mobilized, launched and piloted down river to the drill site by the shallow draft team. Once positioned, Geotechnology's drill crews quickly completed the installation of three deep core holes in less than two weeks. Although river depths at the drill sites were 24 feet at the beginning of the drilling work, river levels rose and fell as much as 7 feet overnight. The jack-up feature of the SD 35/15 allowed the drill crew to adjust the height of the barge to continue operations despite the changing water levels and current. The powerful propulsion system and rapid jack deployment of the SD 35/15 were critical in the successful movement and positioning of the barge at each location. Using the Global Positioning System, each of the borings was drilled within 2 feet of the planned horizontal coordinates.

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.