David Volkert & Associates, Inc.
3809 Moffett Road
Mobile, Alabama 36670
Synergy Earth Systems, Inc.
In 1999, the Owner agreed to construct a barge dock for IPSCO Inc., a Canadian steel company. The Owner elected to construct the facility at a site located on the western bank of the Mobile River, adjacent to IPSCO’s new Mobile Steelworks Mill in Axis, Alabama. Completion of the structure for the unloading facility and for an adjacent access bridge required construction of an earthen platform and a bridge approach embankment. The geotechnical investigation performed at the project site indicated that approximately 5 feet of recently placed fill was underlain by about 30 feet of soft, compressible soil. The presence of this compressible soil made the design and construction of the embankment and bridge approach challenging, with settlement and slope stability being two of the key design considerations.
Synergy Earth Systems, Inc. (SES) was retained directly by the Owner to design and construct the earth platform and associated bridge approach embankment. SES used a matrix design approach to determine which combination of soil improvement technologies would address the key design considerations and result in the most efficient and cost effective design. Several technologies, including horizontal reinforcing geogrids, vertical wick drains, staged construction and surcharging were considered in the matrix. Ultimately, all of the technologies were utilized. A staged construction schedule was utilized to allow the compressible foundation soils to consolidate and gain strength under the newly placed embankment load. A surcharge was also applied in order to pre-consolidate the foundation soils and minimize post-construction settlement.
Construction of the docking facility was performed in two phases. Phase I consisted of construction of the bridge approach embankment. Phase II consisted of construction of the earth platform and sheetpile bulkhead. Phase I of the construction was successfully completed by SES over a one-month period in October-November, 1999. Over 8,000 square yards of geogrid and 130,000 linear feet of wick drains were installed in the bridge approach embankment. Phase II of the construction was begun in June 2000. For this phase of work, over 18,000 square yards of geogrid and 93,000 linear feet of wick drains were installed. As part of the Phase II work, SES designed and constructed approximately 2,800 square feet of wrapped face soil reinforced wall behind the sheetpile bulkhead. This wrapped face retaining wall reduced pressure on the bulkhead and allowed a smaller pile section to be used. The construction is complete and the facility is ready for use.