The Depth of Building Engineering in New Orleans: Reaching Bedrock
New Orleans, known for its unique and often challenging geology, demands meticulous engineering practices from building engineers to ensure the stability and safety of constructions. During the construction of significant structures, engineers face the critical task of determining the depth to bedrock, which can vary significantly across the city.
Geology and the Depth to Bedrock in New Orleans
The depth to bedrock in New Orleans can range widely, generally between 50 to 200 feet or 15 to 60 meters below the surface. However, in some areas, bedrock can be even deeper. The city's unique geology, characterized by soft and compressible sediments, often necessitates extensive drilling to reach stable bedrock, particularly for large structures. Thorough geotechnical investigations are crucial for engineers to determine the specific conditions at each site.
One Shell Plaza and One Shell Square: A Case Study in Building Engineering
The construction of One Shell Plaza in Houston and One Shell Square in New Orleans presents an interesting comparison. Both buildings were structurally similar, yet their foundations differed significantly due to the geological differences in their locations. One Shell Plaza, built on solid bedrock, required no additional measures. However, driving foundation pilings for One Shell Square at 75 feet below the surface led to the loss of pilings, showcasing the challenges faced in New Orleans.
New Orleans' significant buildings are always supported by pilings to ensure stability. This applies not only to large commercial structures but also to substantial residential constructions. The use of pilings is a crucial engineering practice to counteract the soft and compressible nature of New Orleans' subsoil.
Understanding Foundations and Piles
The distinction between foundations and piles is critical in understanding the engineering practices in New Orleans. Foundations typically do not extend to bedrock. Their depth depends on the specific soil conditions and the total weight of the structure they support. For most residential homes, the foundation is supported by the soil itself.
As buildings increase in size and load, the practical capacity of spread foundations is exceeded, necessitating the use of foundation piles. Piles can be driven deep into the ground until the friction generated between the pile and the soil is sufficient to support the building. Driving piles to bedrock is an ideal scenario, but this is not always feasible. Engineers can use friction piles, which can be driven into loose or sandy soils until the friction generated is adequate to support the building load.
The city of Venice, Italy, provides an illustrative example of this practice. Constructed on wooden piles driven into a swampy terrain, Venice's foundations exemplify the importance of friction piles in regions with unstable soils.
It is highly likely that New Orleans shares similar soil conditions, making the use of friction piles a practical and common approach in the city's construction.