Is underpinning separate from shoring?
They serve different purposes but often need to be designed together. Excavation shoring holds back ground; underpinning supports an existing structure whose foundation or load path is affected by the work.
Specialty structural engineering
Underpinning Design
Engineered support for existing foundations affected by nearby excavation, foundation upgrades, or changes in how building loads are carried.
How it works
How underpinning supports an existing foundation
Underpinning adds or changes support beneath an existing structure when excavation or new work could affect its foundation. The design must establish how the existing load is supported before, during, and after installation. Existing drawings may be incomplete, so field verification and coordination with the geotechnical engineer are central to the plan.
Underpinning often shares a site with temporary shoring, but the two solve different problems. The excavation support retains ground around the work; underpinning maintains or transfers support for an existing foundation or element. Their sequences and connections must be compatible.
Site conditions
New support for existing foundations
Excavation beside a building can affect the ground beneath its foundations. Cefali & Associates designs underpinning for existing structures affected by excavation, foundation alterations, or added loads, including how new support is installed and takes over the load in stages.
- Existing foundations
- Foundation drawings and field information show what is supporting the structure and what must stay in place during the work.
- Adjacent excavation
- The excavation sequence and shoring may change how and when existing support is transferred.
- Space to build
- Vaults, basements, utilities, and access routes can limit a conventional underpinning layout.
Engineering services
Support during excavation and foundation construction
Cefali & Associates coordinates underpinning with the existing structure, proposed excavation, geotechnical criteria, and temporary support.
- Existing-condition review
- The design starts with the existing foundations, the loads they carry, and the proposed excavation or alteration.
- Support design
- The underpinning layout provides a way to transfer existing loads to new support as excavation and construction proceed.
- Design coordination
- Connections between existing foundations, new support, and temporary works are developed together. The engagement can also include review of conditions uncovered during construction.
We agree the drawings, calculations, and support during construction with you in the proposal.
Design considerations
Support for the building at every construction stage
Underpinning design starts with reliable information about the existing foundation, the loads it carries, the proposed excavation, and the space available to install support in stages.
- Foundation records
- Existing drawings, surveys, and records of exposed foundations show what is supporting the structure. Gaps in those records may require investigation.
- Temporary load path
- The structure needs support during excavation and installation, before the final underpinning element is fully engaged.
- Access and neighboring work
- Vaults, basements, utilities, shoring braces, and construction traffic can constrain the support method and installation order.
In practice / 755 Fig
The design in practice.
At 755 Fig, an existing vault required underpinning within a narrow, heavily constrained excavation. Cefali coordinated the vault support with corner bracing, walers, horizontal tiebacks, and other temporary shoring.
See the 755 Fig projectRelated project work
Projects involving underpinning
See the systems, site conditions, and construction details from these projects.
Before you begin
Common questions
What information is needed for underpinning design?
As-built drawings, foundation records, a survey, excavation plans, geotechnical recommendations, and photos of accessible existing conditions are useful starting points.
Does excavation beside an existing building always require underpinning?
No. The need depends on the excavation, existing foundation geometry, ground conditions, and how support will be maintained during construction. The neighboring foundation should be evaluated before assuming an underpinning system.
Are existing foundation drawings enough for underpinning design?
They are a starting point. Incomplete records or different conditions in the field may require further investigation before the support can be designed.
Can underpinning be designed without the excavation sequence?
The proposed sequence is a key input because support has to remain in place as excavation and new construction advance. The exact method is developed for the site and contractor’s plan.
Discuss your project
Tell us what you are planning.
Send the drawings, reports, and site information you already have, along with your schedule and the work you need help with. You do not need a complete design package to get in touch.
- Existing structural and foundation drawings or as-builts
- Survey and available records of foundation condition
- Proposed excavation and new foundation plans
- Geotechnical recommendations, utilities, and access constraints