Deep foundations

Definition

Deep foundations are structural elements that transfer the load of a building or structure deep into the ground, beyond the weak surface soil, to reach stronger soil or bedrock. This method is essential for supporting heavy loads and ensuring stability in areas where shallow foundations would not suffice, particularly in locations prone to consolidation settlement or weak subsurface conditions.

5 Must Know Facts For Your Next Test

1. Deep foundations are typically used in areas with high groundwater levels or where surface soils are unstable or compressible.
2. Common types of deep foundations include piles, drilled shafts, and caissons, each chosen based on specific site conditions and load requirements.
3. The design of deep foundations often considers factors such as soil properties, load transfer mechanisms, and potential consolidation settlement.
4. Deep foundations can help mitigate risks associated with settlement by distributing loads over a larger area in deeper, more stable soil layers.
5. Construction methods for deep foundations may involve significant equipment and labor costs, but they provide long-term stability for large structures.

Review Questions

• How do deep foundations function in transferring loads and addressing concerns related to consolidation settlement?
  • Deep foundations work by transferring the loads from a structure down to deeper soil layers that have higher strength and lower compressibility. This is particularly important in areas prone to consolidation settlement where surface soils may not be able to support heavy loads effectively. By extending below weak surface layers to reach stronger soil or bedrock, deep foundations help prevent excessive settlement and maintain structural integrity over time.
• Evaluate the various types of deep foundations and their suitability for different soil conditions.
  • There are several types of deep foundations including piles, drilled shafts, and caissons, each suited to specific soil conditions and load requirements. For example, driven piles are effective in dense sands or gravel while drilled shafts may be preferred in cohesive soils. The selection depends on factors such as soil type, groundwater levels, and the anticipated loads from the structure. Proper evaluation of these conditions ensures the effectiveness of deep foundations in providing support and preventing issues like settlement.
• Assess the implications of selecting deep foundations over shallow foundations concerning cost, construction time, and long-term performance.
  • Choosing deep foundations over shallow ones can have significant implications for construction projects. While deep foundations generally involve higher initial costs due to more complex installation methods and equipment needs, they can offer better long-term performance in unstable soils by reducing risks associated with settlement and structural failure. Additionally, while construction time may be extended due to the intricate nature of installing deep foundations, the investment pays off by ensuring durability and stability of heavy structures in challenging environments.

Related terms

piles: Long cylindrical structures made of concrete, steel, or wood that are driven deep into the ground to provide support for deep foundations.

shaft friction: The resistance generated along the surface of a deep foundation element, like a pile or drilled shaft, due to the soil's adhesion to the foundation material.

bearing capacity: The maximum load per unit area that a foundation can support without failure or excessive settlement.