CONSTRUCTION TECHNIQUES - Underpinning

Underpinning is a technique used to lower an existing basement or to reinforce an existing foundation when adding an additional storey. Underpinning should only be done by a licensed contractor.

As shown below, underpinning is done in stages. The footing is divided into 3' sections and numbered 1,2,3,4....To avoid structural damage, sections marked 1 are excavated, poured and grouted first. When the grout has cured on sections 1, excavation for sections 2 can begin. 

We used a conveyor belt to remove the excavated material from the trench.

We used a conveyor belt to remove the excavated material from the trench.

It is very important to clean the excavated area of loose soil prior to pouring. This photo shows that all disturbed soil has been removed until undisturbed soil is exposed. 

It is very important to clean the excavated area of loose soil prior to pouring. This photo shows that all disturbed soil has been removed until undisturbed soil is exposed.