In urban areas such as Denver or Colorado Springs, where buildings are in close proximity to each other, new commercial projects can present unusual building challenges. Adjacent foundations must be protected from new construction activity. Some foundations in urban environments are older, decayed, or not up to current building codes which exacerbates the problem. Underpinning adjacent foundations can help mitigate the risk of foundation damage. Similarly, underpinning/augmenting the foundation of a building to be repurposed can be a cost-effective alternative to foundation removal and replacement.
These are some of the most common construction projects that need underpinning services across the city.
Rebuilding/Repurposing Existing Buildings
If a building needs substantial reconstruction for repurposing, there’s a good chance that foundation underpinning work will be necessary. Underpinning will enable foundation changes needed to upgrade the building to its new purpose. Once the existing foundation is independently secured through underpinning techniques foundation elements can be added without disrupting the rest of the structure. Once the new foundation elements are in place the old foundation can be safely removed or put back into service in conjunction with the new elements. The result is a foundation system not unlike what you would see in a new build.
One of the common techniques used to deal with these foundation issues is a cantilever needle beam. This uses steel beams and existing columns (and foundation) to add strength to specific areas of the foundation, usually in conjunction with new micropiles on either side. With the support of the beams, the foundation can be expanded and improved, making way for the new construction to follow.
Another common method for augmenting an existing foundation is pier and beam underpinning. This method is similar to using needle beams except beams are placed on newly formed concrete piers which handle the building load while the foundation is either repaired or replaced.
In some cases, it can be economical to add space underground by deepening a foundation. This result can be achieved using the methods above or by installing angled piers directly below the existing foundation walls then attaching the foundation wall to the piers, transferring the load further beneath the foundation. Once secured by the newly installed piers, excavation can take place under the old foundation and new foundation walls can be formed once excavation is complete.
Underpinning Adjacent Foundations
In urban environments, new construction, often times, takes place on a plot that is surrounded by buildings that come all the way up to the property line of the building to be constructed. These projects are particularly challenging, especially if the excavation of the new build is deeper than the foundation of the surrounding building. In this case there is substantial risk that the adjacent foundation will move or settle.
Underpinning can mitigate this condition. By securing the adjacent foundation in place the builder on the new site can freely construct the new building without risk of settlement.
Underpinning the adjacent foundation can be achieved by adding cantilever elements along the property line of the new build. These elements add rigidity to the adjoining foundation and allow for excavation to take place directly next to them.
Another common method of securing an adjacent foundation is to install soil nails and shotcrete beneath the foundation of the surrounding property. A soil nail/shotcrete wall adds rigidity similarly to the cantilever elements described above. This system is limited though, as often times it will require an easement from the surrounding property owner to install underpinning elements beneath their structure.
Naturally, there are plenty of additional situations that call for underpinning, and each underpinning project requires a unique assessment. Common techniques are not always right for a given job. That is precisely why Geocraft Builders looks at each case independently and offers a variety of underpinning solutions. Call today for a free assessment of your underpinning scope.