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A Brief Guide to Underpinning Foundations of Commercial Buildings

Underpinning is a process of increasing the load-bearing capacity of a building's foundation to a deeper elevation, especially a bedrock. Underpinning is used in various situations, such as when the stability of a settled structure is in question. How does it work? A contractor excavates a side of a building to expose the foundation. First, the equipment (for example, pier bracket) is attached to a foundation for support. A contractor then inserts piles into a foundation using the reciprocal load of a building until the piles lie on the bedrock. Here are tips for commercial building owners who plan to underpin their structures. 

Reasons for Underpinning — If the differential or total settlement of a commercial building exceeds a given limit, compression forces might lead to cracks on the foundation, thereby making a building unfit for occupation. Mistakes made during different stages of construction can contribute to a weak foundation and thus, call for underpinning. For example, when cushion material such as sand is not compacted well enough to become dense, then local settlement can occur. Besides, if an adjacent building is being constructed, it can cause foundation damage to your building if necessary precautions are not taken, particularly if the foundation is exposed by excavation. Notably, piles should be driven to standard depth during the construction of a foundation. If you do not drive piles to the required depth or use poor quality piles, then the integrity of a foundation will be compromised.

Piled Raft Underpinning -- In most commercial buildings with multi-levels, foundations are often very deep. Therefore, using common underpinning methods might not work properly. Hence, the use of piled rafts for underpinning such structures is recommended by experienced structural engineers. Besides, a piled raft is used when the underpinning of a whole building is required. Simple excavation tools might not work, especially on hard soils. Therefore, piles are driven to desired levels based on loading conditions in the piled raft underpinning technique. A contractor will then break a structure's footings to make pockets for installing reinforced needle beams. Such beams bear the load of the walls. After that, a ring beam linking all the needle beams is attached before concrete is poured in the foundation. The benefit of the piled raft underpinning method is that it is cost-effective, especially for greater depths. Moreover, the approach does not require invasive access from the exterior of a building. Lastly, a commercial building is strengthened both laterally and in a traversing manner.

Contact a professional who provides underpinning services to learn more.