Buoyancy of buried structures

Definition

Buoyancy of buried structures refers to the upward force that acts on submerged or partially submerged structures due to the displacement of soil or water. This phenomenon is significant in geotechnical engineering, especially during seismic events, where soil liquefaction and lateral spreading can dramatically alter the forces acting on underground facilities. Understanding this concept helps engineers design structures that can withstand the forces exerted by buoyancy in saturated conditions, especially when the surrounding soil loses strength.

5 Must Know Facts For Your Next Test

1. Buoyancy forces can become significant during an earthquake when soil becomes saturated and liquefies, causing structures to float or be pushed upwards.
2. Designing buried structures requires considering the potential for buoyancy forces and ensuring they are counteracted by sufficient weight or anchorage.
3. The degree of buoyancy experienced by a structure depends on its volume, density, and the properties of the surrounding soil or water.
4. Soil types influence buoyancy effects; loose, unconsolidated soils are more prone to liquefaction, increasing the risk of buoyant forces impacting buried structures.
5. Mitigation techniques such as increasing dead weight or using anchors are often employed to counteract the effects of buoyancy on buried structures.

Review Questions

• How does liquefaction influence the buoyancy of buried structures during seismic events?
  • Liquefaction causes saturated soils to lose their load-bearing capacity, which can lead to a significant reduction in effective stress. As a result, the buoyant forces acting on buried structures increase, potentially causing them to float or shift position. Engineers must account for this phenomenon when designing underground facilities in seismically active areas, ensuring that they can withstand potential uplift forces.
• In what ways do lateral spreading and buoyancy interact to impact the stability of underground structures?
  • Lateral spreading involves the horizontal displacement of soil masses following liquefaction, which can impose lateral loads on buried structures. When combined with buoyant forces during liquefaction events, these lateral pressures can compromise a structure's integrity. Therefore, understanding both phenomena is essential for designing resilient underground systems that can resist both vertical uplift from buoyancy and lateral movement from spreading.
• Evaluate how effective stress principles relate to the design strategies used to mitigate buoyancy effects in buried structures.
  • The effective stress principle is foundational in geotechnical engineering, illustrating how pore water pressure influences soil strength. When designing buried structures, engineers apply this principle to assess how changes in pore water pressure during events like liquefaction affect effective stresses. Strategies such as increasing dead weight or using drainage techniques are formulated based on these evaluations to ensure that buoyant forces do not exceed structural resistance during adverse conditions.

Related terms

Liquefaction:

A process in which saturated soil temporarily loses its strength and stiffness due to applied stress, often caused by seismic shaking.

Lateral Spreading:

The horizontal movement of soil masses that occurs when liquefaction happens, potentially leading to significant damage to structures and infrastructure.

Effective Stress Principle: A key concept in soil mechanics that relates the stress carried by soil skeleton to the pore water pressure within the soil, crucial for understanding buoyancy effects.