The first step in underpinning construction is to conduct a thorough site assessment to evaluate the condition of the existing foundation, soil characteristics, structural loads, and any factors contributing to foundation instability. This may involve soil testing, structural inspections, and analysis of building plans and history.

Based on the site assessment, structural engineers design an underpinning solution tailored to the specific needs and conditions of the building. The design may involve various underpinning techniques, such as mass concrete underpinning, mini-piled underpinning, jet grouting, or helical piers, depending on factors such as soil type, foundation depth, access constraints, and project budget.

Once the underpinning design is finalized, excavation begins around the perimeter of the existing foundation to access the footing. Excavation may be performed manually or using mechanical equipment such as excavators or mini-excavators. Care must be taken to minimize disruption to the surrounding structures and utilities.

After excavation, underpinning elements such as concrete piles, steel beams, or helical piers are installed beneath the existing foundation to provide additional support and stability. The underpinning elements are typically placed at regular intervals along the footing, extending into the deeper soil or rock layers.

Depending on the underpinning technique used, grout or concrete may be injected into the voids around the underpinning elements to fill gaps and provide additional support. Reinforcement may also be added to enhance the strength and durability of the underpinning system.

Throughout the underpinning process, monitoring instruments may be installed to track movement, settlement, and other changes in the building's foundation and structure. Adjustments to the underpinning elements may be made as needed to optimize performance and ensure stability.

Once the underpinning construction is complete and the structure has been stabilized, excavated areas are backfilled with suitable material and compacted to restore the site to its original condition. Any disturbed landscaping, pavement, or structures are repaired or replaced as necessary to complete the restoration process.