Abstract:
Environmental remediation of a contaminated site required removal of contaminated sediment in a waterway adjacent to an industrial facility. Existing steel sheet pile bulkheads along the industrial facilities shoreline in Maryland were severely corroded resulting in complete penetrations of the steel sheet piling creating large openings through which soil from the upland areas was entering the adjacent waterway. Because of the ongoing erosion and soil migration, depressions formed on the upland side resulting in loss of support for an existing concrete walkway atop the bulkhead. This condition was a concern because dredging was planned in the waterway in front of the bulkhead for two reasons: 1) continuing erosion causing potentially contaminated sediments to enter the waterway, and 2) potential failure of the structure induced by removal of toe support during dredging.The existing steel bulkheads consisted of a concrete cap and anchor steel rods connected to timber piles through timber wales. The overall conditions of the existing anchors and connections to the existing wall were questionable. Accordingly, a new bulkhead was required to retain soil to prevent recontamination of the dredged waterway and prevent the collapse of the existing structure. A cantilever sheet pile wall was planned and constructed without anchors because it was faster to construct and there would be no anchors that would potentially interfere with upland characterization and remediation work that might be needed. Exposed wall heights ranged from 15 to 19 feet above the dredge line. For the shorter wall, a cost saving approach was taken by reducing the length of alternate sheet pile pairs. Due to corrosive soils and marine exposure, the wall was constructed of marine grade steel with a protective coating to provide a design life of 75 years.During the construction, deeper dredge depths were required, and a soft soil stratum was encountered in the northern bulkhead area that required modification of the design. Modifying the backfill sequence enabled dredging to progress while the modifications were designed. Modifications included removal and replacement of the shorter sheet pile pairs with longer sheet piles. The final bulkhead configuration fulfilled the requirement for geotechnical as well as structural stability enabling the remediation work to proceed apace.