How To Calculate Soil Pressure On Retaining Wall

Rankine Soil Pressure Equation:

\[ P = \frac{1}{2} K_a \gamma h^2 \]

Coefficient of Active Earth Pressure (K_a):

dimensionless

Unit Weight of Soil (γ):

N/m³

Height of Wall (h):

Soil Pressure (P):

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1. What is the Rankine Soil Pressure Equation?

The Rankine soil pressure equation calculates the lateral earth pressure exerted on a retaining wall by soil. It provides the active earth pressure that develops when the wall moves away from the soil mass, which is essential for designing stable retaining structures.

2. How Does the Calculator Work?

The calculator uses the Rankine equation:

\[ P = \frac{1}{2} K_a \gamma h^2 \]

Where:

\( P \) — Soil pressure (Pa)
\( K_a \) — Coefficient of active earth pressure (dimensionless)
\( \gamma \) — Unit weight of soil (N/m³)
\( h \) — Height of the retaining wall (m)

Explanation: The equation calculates the total lateral force per unit length of wall acting at h/3 from the base of the wall.

3. Importance of Soil Pressure Calculation

Details: Accurate soil pressure calculation is crucial for designing safe and stable retaining walls, preventing structural failure, and ensuring proper drainage behind the wall.

4. Using the Calculator

Tips: Enter the coefficient of active earth pressure (typically 0.25-0.33 for common soils), unit weight of soil (typically 16-20 kN/m³), and wall height. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What is the coefficient of active earth pressure (K_a)?
A: K_a = (1 - sinφ)/(1 + sinφ) where φ is the soil's angle of internal friction. It represents the ratio of horizontal to vertical stress in the soil.

Q2: When is the Rankine theory applicable?
A: The theory applies to cohesionless soils with a level backfill and smooth vertical wall. Modifications are needed for cohesive soils or inclined backfills.

Q3: What are typical values for unit weight of soil?
A: Sand: 16-20 kN/m³, Clay: 17-20 kN/m³, Gravel: 18-22 kN/m³. The exact value depends on soil composition and moisture content.

Q4: How does wall height affect soil pressure?
A: Soil pressure increases with the square of wall height, making taller walls significantly more challenging to design and construct.

Q5: What safety factors should be considered?
A: Typical safety factors include 1.5-2.0 for sliding, 1.5-2.0 for overturning, and 2.0-3.0 for bearing capacity. Local building codes provide specific requirements.