What are the key considerations for designing deep foundations in expansive soils?

When designing deep foundations in expansive soils, consider the following key factors:

• Soil characterization: Conduct thorough geotechnical investigations to determine soil properties, including swelling potential and active zone depth.
• Depth of foundation: Extend foundations below the active zone to minimize the effects of soil volume changes.
• Shaft friction: Account for reduced shaft friction due to soil shrinkage during dry periods.
• Uplift forces: Design for potential uplift forces caused by soil heave.
• Moisture control: Implement moisture barriers or drainage systems to maintain consistent soil moisture content.
• Structural design: Use appropriate reinforcement and concrete mix designs to withstand expansive soil pressures.
• Load transfer mechanisms: Consider using bell-bottom piers or under-reamed piles to increase bearing capacity and resist uplift.
• Monitoring: Implement a monitoring program to track foundation performance over time.

Innovative techniques include the use of helical piles, which can be quickly installed and provide immediate load-bearing capacity, and chemical soil stabilization methods to reduce the expansive nature of the soil.