what we do
Underpinning
Underpinning is a specialized design and construction technique used to strengthen, repair or increase the size of a foundation. The process removes soil from beneath an existing foundation in controlled stages, or piers, of defined length before replacing the excavated soil with concrete to form a new foundation beneath the existing one. Piers are excavated in an engineered sequential manner to safely install the underpinning.
While underpinning is most commonly used for remediation or remodeling, it may be needed for new construction in urban environments. Here are a few of the most common use cases:
- Foundation repair or stabilization
- Foundation strengthening – often, to support the addition of upper stories or floors in a building
- Transfer of load, such as when a load-bearing column is moved or removed
- Basement addition
- Elevator construction
- New construction of a building in a dense urban environment that requires support of adjoining, adjacent or nearby structures
For Steele Foundation, underpinning is a core capability built from more than 50 years of successful deep foundation projects. We understand when underpinning should be used, how to apply the technique and how to ensure structural integrity when the project is complete.
Each project is unique. Beginning in the pre-construction stage, we collaborate with construction teams and engineers to determine the underpinning details that will hold up to the soil and site conditions. Our team of experts is practiced at providing cost-effective and safe underpinning solutions to deep foundation challenges.
underpinning Spotlight
Collection 14
When Martha’s Table, a long-term Washington DC charity, moved from its headquarters, it created room for the nearly city-block-sized Collection 14 redevelopment project. The modern, seven-story mixed-use project at 14th and W Street, NW consists of five structures with 230 apartments, 25,000 square feet of retail, 5,300 square feet of offices, a 4,000-square-foot event space and below-grade parking for 75 vehicles.
The developer intended to retain historic street-facing building façades (to the extent possible) to preserve the character of the neighborhood. Steele Foundation’s structural shoring and underpinning for the conversion required complex underground construction and lateral bracing for four existing historic structures in poor condition. This is challenging work that few firms in the region have the expertise and professional staff and craftspeople to perform.
Steele Foundation has been recognized with a 2021 Washington Building Congress Craftsmanship Award in the Sitework category for Underpinning, Foundations and Excavations.