Effective Surcharge given Strip Footing and Bearing Capacity Calculator

Effective Surcharge Formula:

\[ \sigma_{strip} = \frac{q_f - (1 \times C \times N_c + 0.5 \times \gamma \times B \times N_\gamma \times 1)}{N_q} \]

Ultimate Bearing Capacity (qf):

Cohesion (C):

Bearing Capacity Factor (Nc):

Unit Weight of Soil (γ):

N/m³

Width of Footing (B):

Bearing Capacity Factor (Nγ):

Bearing Capacity Factor (Nq):

Effective Surcharge (σstrip): Pa

1. What is Effective Surcharge given Strip Footing?

Definition: Effective surcharge is the additional pressure exerted on the soil due to external loads, such as structures or other surface loads, which are distributed over a strip footing.

Purpose: It helps geotechnical engineers determine the additional load-bearing capacity required for strip footings in foundation design.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \sigma_{strip} = \frac{q_f - (1 \times C \times N_c + 0.5 \times \gamma \times B \times N_\gamma \times 1)}{N_q} \]

Where:

\( \sigma_{strip} \) — Effective surcharge (Pa)
\( q_f \) — Ultimate bearing capacity (Pa)
\( C \) — Cohesion of soil (Pa)
\( N_c \) — Bearing capacity factor dependent on cohesion
\( \gamma \) — Unit weight of soil (N/m³)
\( B \) — Width of footing (m)
\( N_\gamma \) — Bearing capacity factor dependent on unit weight
\( N_q \) — Bearing capacity factor dependent on surcharge

3. Importance of Effective Surcharge Calculation

Details: Proper calculation ensures stable foundation design, prevents excessive settlement, and maintains structural integrity under load.

4. Using the Calculator

Tips: Enter all required parameters with appropriate units. Bearing capacity factors include ±5% uncertainty. All values must be > 0 (except cohesion which can be 0 for cohesionless soils).

5. Frequently Asked Questions (FAQ)

Q1: What is a typical value for Nc, Nγ, and Nq?
A: These depend on soil friction angle. Common values: Nc ≈ 5-37, Nγ ≈ 0-48, Nq ≈ 1-33 (higher values for higher friction angles).

Q2: How is ultimate bearing capacity determined?
A: Through soil testing or empirical relationships based on soil properties and foundation geometry.

Q3: What if my soil has no cohesion (C=0)?
A: Simply enter 0 for cohesion - the formula will account for this automatically.

Q4: Why the ±5% on bearing capacity factors?
A: These factors have inherent uncertainty based on soil variability and empirical determination.

Q5: How does footing width affect the result?
A: Wider footings distribute load over more area, generally reducing effective surcharge requirements.