Questions and Answers
What is the primary purpose of determining the shear strength of soil in geotechnical engineering?
To design foundations and ensure the stability of soil structures
What is the main effect of an increase in water content on the shear strength of soil?
It reduces the shear strength by increasing the pore water pressure
What type of shear strength is measured when the pore water pressure is allowed to dissipate?
Drained shear strength
What is the primary factor that influences the friction angle of soil?
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What type of shear strength is used to analyze the stability of landslides?
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What is the term for the internal resistance of soil to shear, resulting from the interparticle forces between soil particles?
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What is the primary cause of reduced infiltration in compacted soil?
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Which of the following practices is likely to exacerbate soil compaction?
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What is the primary effect of soil compaction on plant growth?
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Which of the following soil types is more susceptible to compaction?
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What is the primary benefit of controlling traffic on soil?
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What is the primary effect of soil moisture on soil compaction?
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Study Notes
Shear Strength of Soil
The shear strength of soil is the maximum stress that a soil can withstand without undergoing shear failure. It is a critical parameter in geotechnical engineering, as it affects the stability of soil structures and the design of foundations.
Factors Affecting Shear Strength
- Cohesion (c): The internal resistance of soil to shear, resulting from the interparticle forces between soil particles.
- Friction Angle (φ): The angle of inclination of the failure plane, influenced by the shape and size of soil particles.
- Normal Stress (σ): The stress perpendicular to the shear plane, affecting the frictional resistance of the soil.
- Water Content: The amount of water in the soil, which can reduce the shear strength by increasing the pore water pressure.
- Density: The compactness of the soil, which can influence the shear strength by affecting the frictional resistance.
Types of Shear Strength
- Undrained Shear Strength (c_u): The shear strength of saturated soil, where the pore water pressure is not allowed to dissipate.
- Drained Shear Strength (c_d): The shear strength of saturated soil, where the pore water pressure is allowed to dissipate.
- Residual Shear Strength (c_r): The shear strength of soil at large deformations, often used to analyze the stability of landslides.
Methods of Measuring Shear Strength
- Triaxial Test: A laboratory test that simulates the confining pressure and shear stress on soil samples.
- Direct Shear Test: A laboratory test that applies a controlled shear stress to soil samples.
- In-Situ Tests: Field tests, such as the vane shear test, that measure the shear strength of soil in its natural state.
Applications of Shear Strength
- Foundation Design: The shear strength of soil is used to determine the bearing capacity and settlement of foundations.
- Slope Stability: The shear strength of soil is used to analyze the stability of slopes and embankments.
- Landslide Analysis: The shear strength of soil is used to evaluate the stability of landslides and determine the risk of failure.
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