Question

General shear failure is common in which of the following soils?

• A. loose silt
• B. soft clay
• C. loose sand
• D. dense sand

Hint:

In geotechnical engineering, understanding soil failure modes is key for foundation design. General shear failure occurs in dense or stiff soils, forming a clear failure plane with bulging. Loose or soft soils often exhibit local or punching shear failure, which affects how foundations are designed to distribute loads.

Answer 1

The Correct Option is D

Step 1: Identify the given data.
The question asks about general shear failure in soils, a concept from geotechnical engineering. The options provided are:
(1) Loose silt
(2) Soft clay
(3) Loose sand
(4) Dense sand
We need to determine which soil type is most prone to general shear failure.
Step 2: Recall the concept of general shear failure.
General shear failure occurs when a soil fails along a well-defined failure plane, typically with significant lateral bulging. This type of failure is characteristic of soils that are dense or stiff, as they can sustain load until a sudden, catastrophic failure occurs. In contrast, loose or soft soils often exhibit local shear failure (partial failure planes) or punching shear failure (sinking with minimal bulging).
Step 3: Analyze each soil type.
Let’s evaluate the behavior of each soil under load to determine its failure mode:
Option 1: Loose Silt
Silt is a fine-grained soil with low cohesion, and "loose" indicates low density. Loose silt typically compresses under load and fails gradually, often exhibiting local shear failure or punching shear failure. General shear failure requires a denser, stronger soil, so this option is unlikely.
Option 2: Soft Clay
Soft clay is a cohesive soil with high water content and low shear strength. Under load, it tends to deform plastically and fails by punching shear failure, where the foundation sinks into the soil with little lateral bulging. General shear failure is not typical for soft clay.
Option 3: Loose Sand
Sand is a granular soil, and "loose" indicates low density with loosely packed particles. Loose sand rearranges under load, leading to local shear failure. It lacks the density to form a well-defined failure plane, making general shear failure uncommon.
Option 4: Dense Sand
Dense sand has tightly packed particles, resulting in high shear strength and stiffness. Under load, it can sustain significant stress before failing suddenly along a distinct failure plane, often with visible bulging. This behavior matches general shear failure, making dense sand the most likely candidate.
Step 4: Apply geotechnical principles.
In soil mechanics, general shear failure is associated with:
Dense granular soils (e.g., dense sand) or very stiff cohesive soils (e.g., hard clay), where the soil’s strength allows a clear failure plane to form.
Loose or soft soils (e.g., loose silt, soft clay, loose sand) typically exhibit local or punching shear failure due to their inability to sustain load without significant deformation.
Among the options, dense sand aligns with the conditions for general shear failure, while the others do not.
Step 5: Select the correct option.
Based on the analysis:
Loose silt, soft clay, and loose sand are prone to local or punching shear failure.
Dense sand exhibits general shear failure due to its high density and strength.
The correct option is (4) dense sand. \[ \boxed{\text{dense sand}} \]