Bearing capacity of soil

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The bearing capacity of soil refers to its ability to support the load applied to it without experiencing excessive settlement or failure. It is an essential consideration in civil engineering and construction projects, as it determines the maximum load that can be safely supported by the soil.

Soil Types and Their Bearing Capacities:
The bearing capacity of soil depends on various factors, including its type, density, moisture content, and compaction. Different soil types have different bearing capacities due to variations in their physical properties. The most common soil types encountered in engineering practice are:

1. Sandy Soils: Sandy soils generally have a higher bearing capacity compared to other soil types. This is because they are composed of larger particles with less interlocking, allowing for better drainage and higher load-bearing capabilities. However, sandy soils may experience settlement under long-term or cyclic loading due to their low cohesion.

2. Clayey Soils: Clayey soils have lower bearing capacities compared to sandy soils. They consist of smaller particles that exhibit higher cohesion but lower permeability. The cohesive nature of clayey soils allows them to resist shear forces but makes them prone to swelling and shrinkage with changes in moisture content. As a result, their bearing capacity can be significantly affected by changes in water content.

3. Silty Soils: Silty soils have intermediate characteristics between sandy and clayey soils. They contain fine particles that offer some cohesion but also allow for drainage. Silty soils generally have lower bearing capacities than sandy soils but higher bearing capacities than clayey soils.

Factors Affecting Bearing Capacity:
Several factors influence the bearing capacity of soil:

1. Soil Density: The density of the soil affects its ability to bear loads. Compacted soils with higher densities generally have greater bearing capacities than loose or poorly compacted soils.

2. Moisture Content: The moisture content of the soil plays a crucial role in its bearing capacity. Optimum moisture content is required for achieving maximum bearing capacity. Excessive moisture can reduce the soil’s strength and increase its compressibility, leading to a decrease in bearing capacity.

3. Shear Strength: The shear strength of the soil is a measure of its resistance to deformation under applied loads. It depends on factors such as cohesion and friction between soil particles. Soils with higher shear strength have greater bearing capacities.

4. Load Duration: The duration of the load applied to the soil also affects its bearing capacity. Short-term loads may result in higher bearing capacities compared to long-term or cyclic loads, which can cause settlement and consolidation.

5. Foundation Depth: The depth at which a foundation is placed influences the bearing capacity of the soil. Deeper foundations can tap into stronger soil layers, increasing the overall bearing capacity.

6. Shape and Size of Foundation: The shape and size of the foundation directly impact the distribution of load on the underlying soil. Irregularly shaped or larger foundations may induce non-uniform stress distribution, affecting the bearing capacity.

Calculating Bearing Capacity:
Engineers use various methods to calculate or estimate the bearing capacity of soil, including:

1. Terzaghi’s Bearing Capacity Theory: Proposed by Karl Terzaghi, this theory provides a general framework for calculating the ultimate bearing capacity of shallow foundations based on soil properties and foundation geometry.

2. Boussinesq’s Theory: Developed by Joseph Boussinesq, this theory considers the influence of point loads on an elastic half-space to estimate the bearing capacity of shallow foundations.

3. Plate Load Test: This field test involves applying a known load to a steel plate placed at the foundation level and measuring the resulting settlement. By analyzing the load-settlement relationship, engineers can estimate the bearing capacity of the soil.

4. Standard Penetration Test (SPT): The SPT is a widely used in-situ test that provides information about the soil’s resistance to penetration. It helps engineers assess the soil’s bearing capacity and other geotechnical properties.

Top 3 Authoritative Reference Publications or Domain Names:
1. “Principles of Geotechnical Engineering” by Braja M. Das and Khaled Sobhan: This textbook provides comprehensive coverage of geotechnical engineering principles, including soil mechanics and foundation design, making it a valuable resource for understanding soil bearing capacity.

2. “Foundation Analysis and Design” by Joseph E. Bowles: This book offers detailed guidance on the analysis and design of various types of foundations, including shallow foundations. It covers topics such as bearing capacity, settlement analysis, and foundation design considerations.

3. “Geotechnical Engineering: Principles and Practices” by Donald P. Coduto, Man-chu Ronald Yeung, and William A. Kitch: This textbook provides a comprehensive overview of geotechnical engineering principles and practices, including soil mechanics, foundation engineering, and geotechnical site investigations. It offers valuable insights into soil behavior and its impact on foundation design.

These authoritative references were used to provide accurate and reliable information on the bearing capacity of soil.

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Arbaj Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

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