Net Ultimate Bearing Capacity given Bearing Capacity Factor Calculator

Net Ultimate Bearing Capacity Formula:

\[ q_{nf} = (C_s \times N_c) + (\sigma_s \times (N_q - 1)) + (0.5 \times \gamma \times B \times N_\gamma) \]

Cohesion of Soil (C_s):

Bearing Capacity Factor (N_c):

Effective Surcharge (σ_s):

kPa

Bearing Capacity Factor (N_q):

Unit Weight of Soil (γ):

N/m³

Width of Footing (B):

Bearing Capacity Factor (N_γ):

Net Ultimate Bearing Capacity (q_nf):

1. What is Net Ultimate Bearing Capacity?

Definition: Net Ultimate Bearing Capacity is the minimum net pressure intensity causing shear failure of the soil beneath a foundation.

Purpose: It helps geotechnical engineers determine the safe load-bearing capacity of soil for foundation design.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ q_{nf} = (C_s \times N_c) + (\sigma_s \times (N_q - 1)) + (0.5 \times \gamma \times B \times N_\gamma) \]

Where:

\( q_{nf} \) — Net Ultimate Bearing Capacity (Pa)
\( C_s \) — Cohesion of Soil (Pa)
\( N_c \) — Bearing Capacity Factor dependent on Cohesion (±5%)
\( \sigma_s \) — Effective Surcharge (kPa converted to Pa)
\( N_q \) — Bearing Capacity Factor dependent on Surcharge (±5%)
\( \gamma \) — Unit Weight of Soil (N/m³)
\( B \) — Width of Footing (m)
\( N_\gamma \) — Bearing Capacity Factor dependent on Unit Weight (±5%)

3. Importance of Bearing Capacity Calculation

Details: Proper calculation ensures foundation stability, prevents excessive settlement, and maintains structural integrity.

4. Using the Calculator

Tips: Enter all required parameters. Bearing capacity factors typically have ±5% variability. Default values are provided for common soil conditions.

5. Frequently Asked Questions (FAQ)

Q1: Why are bearing capacity factors given with ±5%?
A: These factors are empirically derived and can vary slightly depending on soil conditions and analysis methods.

Q2: How do I determine cohesion of soil?
A: Cohesion is typically determined through laboratory tests like unconfined compression tests or field vane shear tests.

Q3: What's a typical range for N_c, N_q, N_γ?
A: For clay (φ=0°): N_c=5.14, N_q=1, N_γ=0. For sand, values increase with friction angle.

Q4: How does footing width affect bearing capacity?
A: Wider footings generally have higher bearing capacity, especially in cohesionless soils.

Q5: Should I apply a safety factor to the result?
A: Yes, typical safety factors range from 2.5-3 for ultimate bearing capacity calculations.