Sheet Pile Used as Permanent Foundation and Retention Systems

The design and construction of sheet pile walls for permanent building foundations and earth retention on four projects in and around Minneapolis, Minnesota USA. The buildings have one to two levels of below grade parking and up to six above grade floor levels. In each case, the below grade parking slabs and the perimeter walls and columns of the superstructure are supported by the sheet pile foundation.

The sheet pile are designed to carry uniform wall loads in the range of 5 to 12 kips per linear foot and concentrated loads of up to 251 kips. The perimeter sheet pile walls are designed for both temporary (during construction) and permanent earth retention. Utilizing the perimeter earth retention system as the permanent foundation maximizes the building footprint on a site and allows building construction in a "top-down" manner. Top-down construction reduces the need for temporary internal bracing or tiebacks to support the earth retention walls by using the building floor slabs to resist lateral earth pressures. It also permits construction of the above grade levels to start before the below grade levels are completed; this can save critical time during the early stages of a project. Design of the sheet pile for both temporary and permanent earth retention follows conventional design methodology, with special attention to each stage of construction.

The interior building excavation and construction sequence is staged to reduce the cantilevered length of sheet pile until permanent floor slabs are constructed, thereby limiting pile deflection. The evaluation of vertical bearing capacity of the sheet pile foundations is based on conventional analyses for friction piles. The vertical bearing capacities estimated by static methods were verified in the field using high strain dynamic testing with a Pile Driving Analyzer (PDA).

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