- Underpins are excavated in a hit and miss sequence, most commonly each of these underpins will be 1.0m – 1.5m in width, an access pit is excavated & excavations in excess of 1.2m are shored with timber.
- Once access has been gained to the correct designed depth the underside of the footing is cleaned, any loose material removed and shutters installed.
- Reinforcement cages are installed, to create a watertight, continuous structure continuity strips or couplers are often introduced between underpins alongside bentonite waterbars where required.
- Concrete is then poured 75mm shy of the underside of existing foundation, once cured the residual is dry packed with a sand/cement mix to ensure load transfer into the underpin.
- For particularly complex loading jacks may be introduced between the new formation and existing footing to ensure transfer.
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