Critical Depth for Cohesive Soil Calculator

Critical Depth Formula:

\[ h_c = \frac{c}{\gamma \times (\tan(I) - \tan(\phi)) \times \cos^2(I)} \]

Cohesion of Soil:

Unit Weight of Soil:

N/m³

Angle of Inclination:

Angle of Internal Friction:

Tolerance:

Critical Depth (m):

1. What is Critical Depth for Cohesive Soil?

Definition: Critical Depth is the depth within a soil profile where the net pressure or stress acting on the soil particles is zero.

Purpose: It helps geotechnical engineers determine the safe depth for excavations and foundations in cohesive soils.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ h_c = \frac{c}{\gamma \times (\tan(I) - \tan(\phi)) \times \cos^2(I)} \]

Where:

\( h_c \) — Critical Depth (meters)
\( c \) — Cohesion of Soil (Pascals)
\( \gamma \) — Unit Weight of Soil (N/m³)
\( I \) — Angle of Inclination (radians)
\( \phi \) — Angle of Internal Friction (radians)

Explanation: The formula calculates the depth at which the soil's cohesive strength balances the gravitational forces acting on it.

3. Importance of Critical Depth Calculation

Details: Proper calculation ensures stable excavations, prevents slope failures, and helps design safe foundations.

4. Using the Calculator

Tips: Enter soil cohesion, unit weight, angles of inclination and internal friction. The tolerance field (default ±5%) provides an acceptable range.

5. Frequently Asked Questions (FAQ)

Q1: What is cohesion in soil mechanics?
A: Cohesion is the ability of soil particles to stick together due to molecular forces and cementation.

Q2: How is angle of internal friction determined?
A: It's typically measured through direct shear tests or triaxial tests in a geotechnical laboratory.

Q3: Why include a tolerance range?
A: Soil properties can vary, so a tolerance range accounts for natural variability and measurement uncertainties.

Q4: What's a typical cohesion value for clay?
A: Soft clay might have 10-20 kPa, while stiff clay can have 50-100 kPa or more.

Q5: When would critical depth be zero?
A: When the angle of inclination equals the angle of internal friction, making the denominator zero.