Allowable bearing capacity

Definition

Allowable bearing capacity is the maximum load per unit area that a foundation can safely support without risking failure or excessive settlement. It is a crucial factor in geotechnical engineering, determining how much weight structures can place on the ground while ensuring stability and safety.

5 Must Know Facts For Your Next Test

1. Allowable bearing capacity is typically determined by applying a factor of safety to the ultimate bearing capacity, ensuring that structures remain safe under expected loads.
2. This value is influenced by various factors such as soil properties, loading conditions, and environmental factors like groundwater levels.
3. When calculating allowable bearing capacity, engineers often use empirical methods and field tests like Standard Penetration Tests (SPT) to obtain accurate soil data.
4. Different bearing capacity theories, like those proposed by Terzaghi, Meyerhof, and Vesic, provide frameworks for estimating allowable bearing capacity based on soil conditions and loading configurations.
5. Allowable bearing capacity plays a critical role in foundation design, impacting the choice between shallow and deep foundations depending on the soil characteristics and load requirements.

Review Questions

• How does the concept of allowable bearing capacity integrate with different soil properties in foundation design?
  • Allowable bearing capacity is heavily influenced by various soil properties such as cohesion, internal friction angle, and density. In foundation design, engineers assess these properties to determine how much load a soil can withstand safely. The interplay between these factors ensures that the chosen foundation type—be it shallow or deep—meets the structural demands while preventing failure due to excessive settlement or other stability issues.
• Compare and contrast the methods used by Terzaghi, Meyerhof, and Vesic to estimate allowable bearing capacity.
  • Terzaghi's method primarily focuses on the theoretical aspects of bearing capacity based on plasticity theory and assumes uniform conditions. In contrast, Meyerhof's approach includes factors like depth and width of foundations and emphasizes the influence of footing shape on load distribution. Vesic's method expands upon these ideas by incorporating both soil properties and loading conditions, providing more comprehensive calculations for complex scenarios. These differences highlight how each theory addresses unique aspects of geotechnical behavior in determining allowable bearing capacity.
• Evaluate how changes in groundwater levels might affect the allowable bearing capacity of soil over time.
  • Groundwater levels play a significant role in determining allowable bearing capacity because they influence the effective stress within the soil. When groundwater rises, pore water pressure increases, reducing the effective stress and consequently lowering the soil's strength. This change can lead to increased settlement or potential failure if not accounted for in design. Over time, fluctuations in groundwater levels may necessitate reevaluating the allowable bearing capacity to ensure that structures remain safe and stable under changing conditions.

Related terms

Ultimate Bearing Capacity: The maximum load per unit area that a soil can support before failure occurs, without considering factors like safety or serviceability.

Factor of Safety: A design principle that provides a margin of safety in engineering, calculated as the ratio of ultimate bearing capacity to allowable bearing capacity.

Settlement: The downward movement of the ground or structure due to loading, which can be influenced by factors like soil type, moisture content, and load magnitude.