TYPES OF BEARING CAPACITY FAILURES OF SOIL
Types of Bearing Capacity Failures of Soil
Soil is a complex and dynamic material that provides support to structures and foundations. One critical aspect of soil behavior is its bearing capacity, which refers to the maximum load a soil can sustain without undergoing excessive settlement or failure. Various types of bearing capacity failures can occur in soil, each with distinct characteristics and causes. Understanding these failures is essential for designing safe and stable structures. This article explores the different types of bearing capacity failures of soil.
1. General Introduction
Bearing capacity failures occur when the applied load on the soil exceeds its capacity to resist that load, leading to instability, settlement, or collapse. These failures can have serious consequences for structures built on or within the soil. Different types of failures are classified based on the mode of failure and the underlying soil characteristics.
2. Shear Failure
Shear failure is one of the most common types of bearing capacity failure in soil. It occurs when the soil experiences excessive shear stress, causing it to deform and rupture along a failure surface. Shear failures can be further categorized into:
2.1. Local Shear Failure
Local shear failure, also known as punching shear failure, happens when the load is concentrated at a small area of the foundation. This type of failure often occurs in footings or slabs with concentrated loads, such as columns. The soil underneath the concentrated load is unable to withstand the high shear stress, leading to a localized failure.
2.2. General Shear Failure
General shear failure, also called overall shear failure, takes place when the entire base of the foundation experiences shear stress that exceeds its shear strength. This type of failure is characterized by a more extensive and widespread collapse of the soil beneath the foundation. General shear failures are commonly observed in large foundations or those subjected to uniform loads.
3. Bearing Capacity Exceedance
Bearing capacity exceedance failure occurs when the applied load surpasses the soil’s bearing capacity without causing shear failure. Instead of rupturing along a failure plane, the soil undergoes excessive settlement and deformation. This type of failure is often seen in loose or poorly compacted soils.
4. Tilting or Rotation Failure
Tilting or rotation failure happens when the foundation tilts or rotates due to uneven bearing capacity across its base. This type of failure is more likely to occur on sloping sites or when the soil’s properties vary significantly across the foundation area. The tilting can lead to structural damage and compromised stability.
5. Base Heave Failure
Base heave failure occurs when the soil beneath a foundation swells or expands, exerting an uplifting force on the foundation. This can happen due to changes in moisture content, frost action, or other environmental factors. Base heave failure can result in uneven settlement and structural distress.
6. Remedies and Prevention
Understanding the types of bearing capacity failures is crucial for engineers and designers to develop appropriate strategies for prevention and mitigation. Some measures to prevent these failures include:
- Conducting thorough site investigations to assess soil properties and variability.
- Properly sizing foundations and distributing loads to avoid localized stress concentrations.
- Improving soil compaction and reinforcement to enhance shear strength.
- Implementing proper drainage systems to control moisture content and prevent base heave.
7. Conclusion
In conclusion, bearing capacity failures of soil can have serious implications for the stability and safety of structures. Shear failure, bearing capacity exceedance, tilting or rotation failure, and base heave failure are some of the key failure types that engineers should be aware of during the design and construction phases. By understanding the causes and characteristics of these failures, professionals can take appropriate measures to prevent them and ensure the longevity of structures built on soil.
