Milwaukee DMMF – Tandem Sheet Pile Containment, Design and Construction

Abstract: Milwaukee Metropolitan Sewerage District (MMSD) has initiated the Milwaukee Estuary Dredge Material Management Facility (DMMF) project to provide disposal capacity for approximately 1.9 million cubic yards of contaminated spoils dredged from the Milwaukee, Menomonee, and Kinnickinnic Rivers and the Milwaukee Bay. DMMF’s typically utilize earthen dikes for containment of the dredge material. The Milwaukee DMMF, however, utilizes tandem (double) combi-wall structures (combination steel pipe pile and steel sheet pile structures) on the waterside to minimize offset from the navigation channel, provide maximum internal storage capacity, and allow construction of a continuous slurry wall as a cutoff for contaminated groundwater. This is the second such facility to be constructed in the Great Lakes. This paper discusses the planning, design, and initial construction phases for the tandem combi-wall containment structures.
Ensuring stability of the containment necessitated innovative techniques for analyzing tandem bulkhead structures, where parallel rows of sheet piling form a relatively narrow containment for earth fill between, with significant structure-soil-structure interaction between the two walls. There is very limited technical literature available for this wall configuration, despite being increasingly common. Comparison will be made between finite element techniques and proposed simplified (i.e., limit equilibrium) methods for analysis of this type of structure.
The construction sequence dictates that after pre-dredging to remove soft alluvial sediments, granular borrow materials will be placed between the cross-tied walls and compacted with vibro-floatation techniques. To install the continuous cutoff wall, temporary wale beams are mounted to the external face of the combi-wall, jacks are placed to relieve tie rod tension, then the tie rod is rotated to clear the cutoff wall area. After the cutoff wall construction, the procedure is reversed to re-tension the tie rods and slide the wale beam to the next adjacent location.
Filling of the DMMF will proceed for approximately 15 to 25 years. Following final fill placement, the facility will be capped and turned over to the Port of Milwaukee for beneficial use as a deep-water berth and associated uplands for commercial shipping purposes.

How does this project / topic contribute to the advancement of the industry and profession?: Dredge material management facilities (DMMFs) typically utilize earthen dikes for containment of the infill material. The Milwaukee DMMF utilizes tandem (double) sheet piles structures in order to minimize offset from the navigation channel, provide maximum internal storage capacity, and allow construction of a continuous environmental cutoff wall. This is the second such facility to be constructed in the Great Lakes.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: This topic will discuss innovative design techniques for tandem (double) combi-wall structures, where parallel rows of bulkhead form a relatively narrow containment for earth fill between, with significant structure-soil-structure interaction between the two walls. There is very limited technical literature available for this structural configuration, despite the fact that they are increasingly common. Comparison will be made between limit equilibrium, soil spring, and finite element techniques for analysis of this type of structure.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The most challenging technical aspect has been determining a reasonable construction sequence to allow tie rods to be sequentially removed in order to facilitate construction of the continuous cutoff wall.
F To install the cutoff wall, temporary wale beams are mounted to the external face of the combi-wall, jacks are placed to relieve tie rod tension, then the tie rod is rotated to clear the cutoff wall area. After cutoff wall installation, the procedure is reversed to re-tension the tie rods and slide the wale beam to the next adjacent location.

Who is the target audience for this paper?: This project will be of interest and benefit to port planners and design engineers, specifically for dredge material disposal and areas with limited developable land for heavy industry.