Bearing Capacity for Local Shear Failure Calculator

Ultimate Bearing Capacity Formula:

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

Cohesion of Soil (Cs):

kPa

Bearing Capacity Factor (Nc):

Effective Surcharge (σs):

kPa

Bearing Capacity Factor (Nq):

Unit Weight of Soil (γ):

kN/m³

Width of Footing (B):

Bearing Capacity Factor (Nγ):

Ultimate Bearing Capacity (qf):

1. What is Bearing Capacity for Local Shear Failure?

Definition: This calculator determines the ultimate bearing capacity of soil under local shear failure conditions, which occurs when there is significant compression but only partial development of shear surfaces.

Purpose: It helps geotechnical engineers and foundation designers assess the load-bearing capacity of soils for shallow foundation design.

2. How Does the Calculator Work?

The calculator uses Terzaghi's modified bearing capacity formula for local shear failure:

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

Where:

\( q_f \) — Ultimate bearing capacity (kPa)
\( C_s \) — Cohesion of soil (kPa)
\( N_c, N_q, N_\gamma \) — Bearing capacity factors (±5% typical variation)
\( \sigma_s \) — Effective surcharge (kPa)
\( \gamma \) — Unit weight of soil (kN/m³)
\( B \) — Width of footing (m)

Explanation: The formula accounts for soil cohesion, surcharge pressure, and soil weight contributions to bearing capacity, with reduced cohesion for local shear conditions.

3. Importance of Bearing Capacity Calculation

Details: Accurate bearing capacity estimation prevents foundation failures, ensures structural stability, and optimizes foundation design costs.

4. Using the Calculator

Tips: Enter all required parameters. Bearing capacity factors typically have ±5% variation. Ensure width is the shorter dimension for rectangular footings.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between general and local shear failure?
A: General shear shows distinct failure surfaces, while local shear has significant compression with only partial shear surface development.

Q2: Why is cohesion reduced by 2/3 for local shear?
A: This reduction accounts for the partial mobilization of soil shear strength in local shear conditions.

Q3: How do I determine bearing capacity factors?
A: Factors depend on soil friction angle - use standard geotechnical tables or our Bearing Capacity Factor Calculator.

Q4: What's a typical safety factor for bearing capacity?
A: Typically 2.5-3.0 for local shear conditions, but depends on soil variability and importance of structure.

Q5: When does local shear typically occur?
A: In loose sands or soft clays, or when foundations are relatively wide compared to depth.