Foundation Engineering

Purpose of Field Tests for Bearing Capacity Evaluation

• Field tests assess the actual bearing capacity of soil in situ, providing more accurate results than laboratory tests.
• They help identify site-specific variations in soil properties that affect foundation performance and safety.

Factors Affecting Safe Bearing Capacity of a Foundation

• Soil type: Cohesive and granulated soils differ significantly in strength and stability.
• Moisture content: Changes in moisture influence soil density and strength.
• Load conditions: The magnitude and type of loads applied (static or dynamic) affect capacity.

Methods for Soil Exploration

• Common soil exploration methods include borehole drilling, sampling, and in-situ tests like Standard Penetration Test (SPT).
• Geophysical methods such as seismic refraction and electrical resistivity can also be used for subsurface investigation.

Consolidation and Settlement

• Consolidation refers to the gradual settlement of soil due to the expulsion of water from its pores, leading to increased density over time.
• Primary consolidation is a major component causing long-term settlement in saturated cohesive soils.

Soil Types Requiring Special Guidelines for Foundations

• Expansive clay soils need additional considerations due to their significant shrink-swell behavior.
• Silty and organic soils often require special measures as they can exhibit unpredictable changes in strength with moisture variations.

Methods for Analyzing Bearing Capacity of Soil

• Limit State Method and Terzaghi-Wegman method are commonly used for calculating soil bearing capacity.
• Finite Element Method (FEM) provides a detailed analysis of complex soil behavior under load.

Immediate Settlement After Foundation Construction

• Immediate settlement is referred to as "elastic settlement," occurring quickly due to the load application on newly constructed foundations.

Effect of Water Table on Bearing Capacity of Soil

• A high water table can reduce soil effective stress, significantly lowering the bearing capacity.
• Seasonal variations in the water table must be considered in the design of foundations for long-term performance.