Effective Surcharge given Bearing Capacity for Local Shear Failure Calculator

Effective Surcharge Formula:

\[ \sigma_s = \frac{q_f - \left(\frac{2}{3} \times C_s \times N_c + 0.5 \times \gamma \times B \times N_\gamma\right)}{N_q} \]

Ultimate Bearing Capacity (kPa):

Cohesion of Soil (kPa):

Bearing Capacity Factor (Nc):

Unit Weight of Soil (kN/m³):

Width of Footing (m):

Bearing Capacity Factor (Nγ):

Bearing Capacity Factor (Nq):

Effective Surcharge (kPa):

1. What is Effective Surcharge in Bearing Capacity?

Definition: Effective surcharge refers to the vertical pressure acting over the ground surface in addition to basic earth pressure, which influences the bearing capacity of soil.

Purpose: This calculation helps geotechnical engineers determine the additional load that can be safely applied to soil foundations.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \sigma_s = \frac{q_f - \left(\frac{2}{3} \times C_s \times N_c + 0.5 \times \gamma \times B \times N_\gamma\right)}{N_q} \]

Where:

\( \sigma_s \) — Effective surcharge (kPa)
\( q_f \) — Ultimate bearing capacity (kPa)
\( C_s \) — Cohesion of soil (kPa)
\( N_c \) — Bearing capacity factor dependent on cohesion
\( \gamma \) — Unit weight of soil (kN/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: Accurate calculation ensures proper foundation design, prevents excessive settlement, and maintains structural stability.

4. Using the Calculator

Tips: Enter all required parameters. The calculator accounts for local shear failure conditions by using 2/3 of the cohesion value.

5. Frequently Asked Questions (FAQ)

Q1: What is local shear failure?
A: Local shear failure occurs when only a portion of the soil beneath the foundation reaches failure, with limited vertical movement.

Q2: Why use 2/3 of cohesion?
A: For local shear failure conditions, Terzaghi recommended reducing cohesion to two-thirds of its actual value.

Q3: How do I determine bearing capacity factors?
A: These depend on soil friction angle and can be found in geotechnical tables or calculated using specific formulas.

Q4: What's a typical range for effective surcharge?
A: Values typically range from 10-100 kPa depending on soil conditions and loading.

Q5: Does this account for water table effects?
A: No, for submerged conditions you must use buoyant unit weight and consider pore water pressure separately.