Relationship Between Soil Cohesion and Unconfined Compressive Strength

Definition:
Soil cohesion (c) is the internal molecular attraction that holds together the particles of a soil and is responsible for the shear strength of the soil.

Unconfined compressive strength (qu) is the maximum axial compressive stress that a cylindrical soil specimen can withstand without lateral support.

Relationship:
The relationship between soil cohesion (c) and unconfined compressive strength (qu) is given by:

c = qu/2

This means that soil cohesion is equal to half of the unconfined compressive strength.

Explanation:
The relationship between soil cohesion and unconfined compressive strength can be derived from the Mohr-Coulomb failure criterion. The Mohr-Coulomb failure criterion is an equation that describes the relationship between the shear strength of a soil and the normal stress acting on it.

The equation is given as:

τ = c + σtan(φ)

where,

τ = shear stress
c = soil cohesion
σ = normal stress
φ = angle of internal friction

When the normal stress is zero, the equation simplifies to:

τ = c

This means that when there is no normal stress acting on the soil, the shear stress is equal to the soil cohesion. In other words, soil cohesion is the shear strength of the soil when there is no normal stress acting on it.

When a normal stress is applied to the soil, the shear strength of the soil increases due to the frictional resistance between the particles. The increase in shear strength is given by:

τ = σtan(φ)

The unconfined compressive strength is the maximum axial compressive stress that a cylindrical soil specimen can withstand without lateral support. It can be calculated from the following equation:

qu = 2c + σtan(φ)

When σ = 0, the equation simplifies to:

qu = 2c

This means that the unconfined compressive strength is equal to twice the soil cohesion when there is no normal stress acting on the soil.

Therefore, the relationship between soil cohesion (c) and unconfined compressive strength (qu) is given by:

c = qu/2

Conclusion:
The relationship between soil cohesion and unconfined compressive strength is important in geotechnical engineering as it allows engineers to estimate the strength of a soil based on simple laboratory tests. The relationship is derived from the Mohr-Coulomb failure criterion, which is a fundamental equation in soil mechanics.

Relationship between Soil Cohesion and Unconfined Compressive Strength

Definition: Soil cohesion is the shear strength of a soil in the absence of normal stress.

Definition: Unconfined compressive strength (qu) is the maximum stress that an unconfined cylindrical specimen can withstand before failure occurs.

The relationship between soil cohesion (c) and unconfined compressive strength (qu) is given as c = qu/2. This means that the soil cohesion is half of the unconfined compressive strength.

Explanation:

Soil cohesion is a measure of the shear strength of a soil in the absence of normal stress. It is the result of the chemical and physical bonding between the soil particles. The cohesion of a soil is affected by factors such as soil type, moisture content, and compaction.

Unconfined compressive strength is a measure of the maximum stress that an unconfined cylindrical specimen can withstand before failure occurs. It is an important parameter in soil mechanics and is used to determine the soil's ability to support structures.

The relationship between soil cohesion and unconfined compressive strength can be understood by examining the behavior of soil under stress. When a soil is subjected to a compressive stress, the soil particles are pushed closer together. The soil's resistance to this compression is a function of its shear strength and its ability to maintain its structure.

The unconfined compressive strength measures the maximum stress that a soil can withstand before it fails. This stress is applied uniformly to the soil specimen, and it is assumed that the soil particles are not bonded together. In contrast, soil cohesion is a measure of the shear strength of the soil, which is a result of the bonding between soil particles.

The relationship between soil cohesion and unconfined compressive strength is given by c = qu/2. This means that the soil cohesion is half of the unconfined compressive strength. This relationship is based on the assumption that the soil is homogeneous, isotropic, and the stress is uniformly distributed.

Conclusion:

In conclusion, the relationship between soil cohesion and unconfined compressive strength is an important parameter in soil mechanics. The soil cohesion is half of the unconfined compressive strength, and this relationship is based on the assumption of homogeneous and isotropic soil. Understanding this relationship is essential for designing and constructing safe and stable structures on soil.