Cohesion of Soil for Purely Cohesive Soil given Depth of Footing Calculator

Cohesion of Soil Formula:

\[ C_s = \frac{q_f - (\gamma \times D \times N_q)}{N_c} \]

Ultimate Bearing Capacity:

Unit Weight of Soil:

N/m³

Depth of Footing:

Bearing Capacity Factor (Nq):

Bearing Capacity Factor (Nc):

Cohesion of Soil (Cs): Pa

1. What is Cohesion of Soil for Purely Cohesive Soil?

Definition: Cohesion of soil is the ability of soil particles to hold together, representing the shear strength or binding force between like particles in soil structure.

Purpose: This calculation is essential in geotechnical engineering for foundation design, slope stability analysis, and earth pressure calculations.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ C_s = \frac{q_f - (\gamma \times D \times N_q)}{N_c} \]

Where:

\( C_s \) — Cohesion of Soil (Pa)
\( q_f \) — Ultimate Bearing Capacity (Pa)
\( \gamma \) — Unit Weight of Soil (N/m³)
\( D \) — Depth of Footing (m)
\( N_q \) — Bearing Capacity Factor dependent on Surcharge (±5%)
\( N_c \) — Bearing Capacity Factor dependent on Cohesion (±5%)

Explanation: The formula calculates soil cohesion by accounting for bearing capacity, soil weight, footing depth, and bearing capacity factors.

3. Importance of Cohesion Calculation

Details: Accurate cohesion values are critical for safe foundation design, preventing structural failures, and ensuring long-term stability of constructions.

4. Using the Calculator

Tips: Enter all required parameters with positive values. The bearing capacity factors (Nq and Nc) typically have ±5% variability.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical range for cohesion in cohesive soils?
A: Cohesion values typically range from 10 kPa (soft clay) to 200 kPa (stiff clay).

Q2: Why are Nq and Nc factors given with ±5%?
A: These factors are empirical and can vary slightly based on soil conditions and testing methods.

Q3: How does footing depth affect cohesion calculation?
A: Deeper footings generally require higher cohesion values due to increased overburden pressure.

Q4: What if I get a negative cohesion value?
A: Negative values indicate invalid input parameters - check your ultimate bearing capacity and other inputs.

Q5: How accurate is this calculation for field conditions?
A: This provides an estimate - always verify with field tests and consider safety factors in design.