Underpinning, in the context of Australian commercial construction projects, refers to the process of reinforcing or strengthening an existing building foundation to ensure its stability and structural integrity . This construction technique involves adding extra footings beside and under the existing foundation to transfer the weight of the building to a more stable soil stratum
Purpose of Underpinning
The primary purpose of underpinning is to:
- Prevent collapse due to excessive settlement or other failure conditions
- Allow the loads on a building to be safely transferred to a stable foundation
- Strengthen or increase the depth of an existing foundation
- Repair damaged or deteriorated foundations
Techniques Used in Underpinning
Various techniques are used in underpinning, including:
- Extending the pre-existing foundation to a stable stratum
- Injecting a 2-part resin under the affected area of the slab to fill voids and stabilize the foundation
- Lifting a concrete slab to level and stabilize it, also known as slab jacking or slab lifting
The process of underpinning typically involves the following steps:
Site investigation and assessment: The first step in underpinning is to thoroughly investigate and assess the existing foundations and the surrounding soil conditions. This may involve soil testing, structural analysis, and inspections to determine the extent of the problem and the most appropriate underpinning solution.
Design and planning: Based on the site investigation and assessment, a detailed design and plan for the underpinning works are developed. This may involve selecting the appropriate underpinning method, determining the depth and width of the underpinning, and specifying the materials and construction techniques to be used.
Preparation and excavation: The area around the existing foundations is prepared for underpinning by removing any vegetation, debris, or other obstructions. Excavation may be required to expose the existing foundations and create space for the underpinning works.
Installation of underpinning elements: The chosen underpinning method is then implemented. This may involve installing concrete piles, steel beams, or other structural elements to support the existing foundations and transfer the load to a deeper and more stable soil layer.
Monitoring and testing: Throughout the underpinning process, the building's stability and performance are closely monitored and tested to ensure that the underpinning works are effective and that the building remains safe and stable. This may involve regular inspections, structural monitoring, and testing of the soil and foundations.
Backfilling and reinstatement: Once the underpinning works are complete, the excavated area is backfilled with soil, and the site is reinstated to its original condition. This may involve landscaping, paving, or other works to restore the area to its original state.
Underpinning is a complex and specialized construction technique that requires the expertise of experienced engineers, contractors, and construction professionals. It is essential to carefully plan and execute underpinning works to ensure the safety and stability of the existing structure and to avoid any potential damage or collapse during the construction process.
