Underpinning · Cambridge
Foundation Underpinning, Cambridge
An existing foundation needed to carry new loads while a deeper adjacent excavation advanced nearby.
The problem
An existing foundation needed to carry new loads while a deeper adjacent excavation advanced nearby.
The engineered approach
Driven precast concrete piles were installed in sequenced sections beneath the footing, transferring load to competent strata and arresting settlement.
Outcomes for the GC
- Existing structure stabilized for new loads
- No measurable settlement to the supported structure
- Zero recordable safety incidents
How we built it
A schematic section of the underpinning system for this Cambridge job. Scroll to build it in construction order, or select a callout to read the detail.
Callouts
Select a numbered part below to read what it is and what it does.
- The pre-existing wall and spread footing bear in unsuitable urban fill; underpinning carries their load deeper without demolishing the structure above.
- A short approach pit is hand-excavated beneath the footing in sequenced sections, so only a limited length of foundation is unsupported at any time.
- Precast concrete segments (typically 12–14 in square, 3–4 ft long) are driven or jacked down and spliced, advancing the pile toward a competent bearing stratum.
- Each pile is driven to refusal in dense glacial till, the competent founding stratum reached near 50 ft here that develops the design end-bearing capacity.
- Steel wedges and a dry-pack mortar are set between the pile heads and the footing soffit, transferring the structural load onto the new piles and arresting settlement.
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