Engineering Term of the Month – “ Underpinning ”
Underpinning is one of several methods used to repair and strengthen building foundations , often involving the installation of permanent or temporary supports . This enables the foundation to be lowered in elevation and increases the resulting bearing capacity of the structure , assisting with the transfer of weight to the surrounding soil . Jet grouting and the use of micropiles are common , traditional methods utilized in the underpinning process , however the term has evolved over the years to include any methodology that improves or strengthens an existing foundation .
There are many factors / reasons that could cause underpinning to be required , such as :
‐ A new basement level is needed beneath an existing structure . ‐ To stabilize the foundation soil to improve resistance against environmental factors . ‐ Degradation of timber piles causes structural settlement due to water table fluctuations . ‐ Adjacent construction or excavation could potentially affect the supporting soil . ‐ The existing foundation is weak , under‐designed , or unstable . 1
Some example of underpinning methods include :
‐ Mass Pour – most common due to low cost and ability to resist heavy foundation loads . Solid , continuous foundation poured in stages beneath the existing footing .
‐ Beam and Base – reinforced concrete beam constructed below foundation to replace existing footing . New beam transfers load to concrete base , spreading load evenly across the soil . ‐ Mini / Micro‐Piles – used where ground conditions are variable or access is limited . Piles are driven deep enough into the ground to allow the pile tip to rest on stable soil . 2
Source : Accurate Basement Repair
Sources :
1 https :// theconstructor . org / building / underpinning‐methods‐procedure‐applications / 14480 / 2 https :// www . hensonarchitect . com / what‐is‐underpinning /
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