Cohesion of Soil for Rectangular Footing given Shape Factor Calculator

Cohesion Formula:

\[ C = \frac{q_{fc} - (\sigma_s \times N_q + 0.5 \times \gamma \times B \times N_\gamma \times (1 - 0.2 \times \frac{B}{L}))}{N_c \times (1 + 0.3 \times \frac{B}{L})} \]

Ultimate Bearing Capacity (kPa):

kPa

Effective Surcharge (kPa):

kPa

Bearing Capacity Factor (Surcharge):

Unit Weight of Soil (kN/m³):

kN/m³

Width of Footing (m):

Bearing Capacity Factor (Unit Weight):

Length of Footing (m):

Bearing Capacity Factor (Cohesion):

Cohesion of Soil (kPa):

1. What is Cohesion of Soil for Rectangular Footing?

Definition: This calculator determines the cohesion of soil beneath a rectangular footing considering shape factors that account for the footing's dimensions.

Purpose: It helps geotechnical engineers and foundation designers evaluate soil strength parameters for rectangular foundation design.

2. How Does the Calculator Work?

The calculator uses the modified bearing capacity formula:

\[ C = \frac{q_{fc} - (\sigma_s \times N_q + 0.5 \times \gamma \times B \times N_\gamma \times (1 - 0.2 \times \frac{B}{L}))}{N_c \times (1 + 0.3 \times \frac{B}{L})} \]

Where:

\( C \) — Cohesion of soil (kPa)
\( q_{fc} \) — Ultimate bearing capacity (kPa)
\( \sigma_s \) — Effective surcharge (kPa)
\( N_q, N_\gamma, N_c \) — Bearing capacity factors
\( \gamma \) — Unit weight of soil (kN/m³)
\( B \) — Width of footing (m)
\( L \) — Length of footing (m)

3. Importance of Cohesion Calculation

Details: Accurate cohesion estimation ensures proper foundation design, prevents settlement issues, and maintains structural stability.

4. Using the Calculator

Tips: Enter all required parameters with correct units. Bearing capacity factors typically have ±5% variability.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for bearing capacity factors?
A: Values depend on soil type and friction angle. Common ranges: Nc (5-37), Nq (1-23), Nγ (0-20).

Q2: Why include shape factors?
A: Shape factors account for how rectangular footing dimensions affect bearing capacity compared to strip footings.

Q3: How do I determine ultimate bearing capacity?
A: Through plate load tests or empirical correlations with soil properties.

Q4: What if my footing is square?
A: Set B = L. The shape factors will simplify to 0.8 for Nγ term and 1.3 for Nc term.

Q5: How accurate is this calculation?
A: Results are estimates. Actual cohesion should be verified through laboratory testing.