Unit Weight Of Soil Under Strip Footing For General Shear Failure Calculator

Formula Used:

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

Net Ultimate BC (q_nu):

Pascal

Cohesion in Soil (C):

Pascal

Bearing Capacity Factor (N_c):

Effective Surcharge (σ_s):

Pascal

Bearing Capacity Factor (N_q):

Width of Footing (B):

Meter

Bearing Capacity Factor (N_γ):

Unit Weight of Soil (γ):

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1. What is Unit Weight of Soil Under Strip Footing?

The unit weight of soil under a strip footing refers to the weight per unit volume of soil that contributes to the bearing capacity of the foundation. It is a critical parameter in geotechnical engineering for designing foundations that can safely support structural loads without shear failure.

2. How Does the Calculator Work?

The calculator uses the formula for general shear failure:

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

Where:

\( \gamma \) — Unit Weight of Soil (N/m³)
\( q_{nu} \) — Net Ultimate Bearing Capacity (Pa)
\( C \) — Cohesion in Soil (Pa)
\( N_c \) — Bearing Capacity Factor dependent on Cohesion
\( \sigma_s \) — Effective Surcharge (Pa)
\( N_q \) — Bearing Capacity Factor dependent on Surcharge
\( B \) — Width of Footing (m)
\( N_\gamma \) — Bearing Capacity Factor dependent on Unit Weight

Explanation: This formula calculates the unit weight of soil required to achieve a specific bearing capacity, considering soil cohesion, surcharge pressure, and footing dimensions.

3. Importance of Unit Weight Calculation

Details: Accurate calculation of unit weight is essential for foundation design, slope stability analysis, and earth pressure calculations. It helps engineers determine the soil's ability to support structural loads without excessive settlement or failure.

4. Using the Calculator

Tips: Enter all values in appropriate units (Pascal for pressures, meters for length). Ensure bearing capacity factors are appropriate for your soil type and conditions. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is general shear failure?
A: General shear failure occurs when a continuous failure surface develops from the footing to the ground surface, characterized by sudden and catastrophic foundation failure with well-defined rupture patterns.

Q2: How do bearing capacity factors vary?
A: Bearing capacity factors (N_c, N_q, N_γ) depend on the soil's angle of internal friction and are typically obtained from established tables or formulas in geotechnical engineering.

Q3: What is effective surcharge?
A: Effective surcharge refers to the vertical pressure at the foundation level due to overburden soil or any additional load acting on the ground surface around the foundation.

Q4: When is this formula applicable?
A: This formula is specifically for strip footings experiencing general shear failure in cohesive-frictional soils. Different formulas apply for local or punching shear failures.

Q5: What are typical unit weight values for soils?
A: Unit weight typically ranges from 16-22 kN/m³ for most soils, with sands being lighter (15-18 kN/m³) and clays being heavier (18-22 kN/m³).