Bearing capacity failures occur when the forces on the soil exceed its shear strength, causing foundation issues. There are three types of shear failures – general, local, and punching shear failures. Let’s explore these types of bearing capacity failures in soil.
Understanding Soil Bearing Capacity:
Soil bearing capacity is the ability of soil to withstand applied loads. It depends on the soil’s density, shear strength, and the depth of load application. The bearing capacity is the maximum load per unit area the soil can handle without displacement, calculated by dividing it by the factor of safety.
Ultimate Bearing Capacity (Qu):
Ultimate bearing capacity is the maximum pressure at the foundation base, causing shear failure. It’s the minimum pressure that would result in shear failure if the soil is right under the foundation.
Types of Bearing Capacity Failures:
- General Shear Failure:
- Rupture of underlying soil with bulging around the footing.
- Settlement on one side causes tilting of the structure.
- Happens at low strain with a well-defined failure surface.
- Local Shear Failure:
- Ultimate shear strength mobilized locally along the sliding surface.
- Significant soil compression beneath the footing.
- Bulging on both sides, less than general shear failure.
- No tilting of the footing, a poorly defined failure surface.
- Punching Shear Failure:
- Strong compression beneath the footing with vertical shearing.
- Catastrophic failure with no obvious warning.
- Common in loose, soft soil, and at higher elevations.
- Footing penetrates without surface bulging.
Conclusion:
Understanding soil-bearing capacity is crucial in construction design. Different failures like general shear, local shear, and punching shear can occur, affecting the stability of structures. Knowing these types helps in preventing failures and ensuring a strong foundation.