Effective Surcharge given Bearing Capacity for Circular Footing Calculator

Effective Surcharge Formula:

\[ \sigma_s = q_f - (1.3 \times C \times N_c) \]

Effective Surcharge (kPa):

1. What is Effective Surcharge in Circular Footing?

Definition: Effective Surcharge (σₛ) is the vertical pressure acting over the ground surface in addition to basic earth pressure, calculated for circular footings.

Purpose: It helps determine the additional load capacity a circular footing can support beyond its own weight.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \sigma_s = q_f - (1.3 \times C \times N_c) \]

Where:

\( \sigma_s \) — Effective surcharge (kPa)
\( q_f \) — Ultimate bearing capacity (kPa)
\( C \) — Cohesion in soil (kPa)
\( N_c \) — Bearing capacity factor dependent on cohesion

Explanation: The formula subtracts the cohesion component from the ultimate bearing capacity to find the effective surcharge.

3. Importance of Effective Surcharge Calculation

Details: Proper calculation ensures structural stability and prevents foundation failure by accounting for additional surface loads.

4. Using the Calculator

Tips: Enter the ultimate bearing capacity, soil cohesion, and bearing capacity factor. All values must be > 0. Results include ±5% tolerance.

5. Frequently Asked Questions (FAQ)

Q1: Why is the 1.3 factor used in the formula?
A: The 1.3 factor accounts for the shape effect of circular footings compared to strip footings.

Q2: What's a typical range for Nc values?
A: For cohesive soils, Nc typically ranges from 5.14 to 9, depending on depth and soil conditions.

Q3: How does cohesion affect the result?
A: Higher cohesion values reduce the effective surcharge capacity, as more capacity is used to resist shear.

Q4: What units should I use?
A: All inputs should be in kPa (kilopascals) for consistent results.

Q5: Does this calculation include safety factors?
A: No, this gives theoretical capacity. Apply appropriate safety factors for design purposes.