A 10 m x 6 m mat foundation is placed at 2.0 m depth in sand where the average value of N60 is 23. Determine the allowable net pressure that would limit the settlement to 75 mm,

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Chapter14: Sheet-pile Walls
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A 10 m x 6 m mat foundation is placed at 2.0 m depth in sand where the average value of N60 is 23. Determine the allowable net pressure that would limit the settlement to 75 mm, using the following equations.

 

 

### Bearing Capacity of Foundations

The following equation is used to determine the net bearing capacity (\(q_{net}\)) of a foundation:

\[
q_{net}(kN/m^2) = \frac{N_{60}}{0.08} \left( \frac{B + 0.3}{B} \right)^2 F_d \left( \frac{S_e}{25} \right) \quad \text{(for \(B > 1.22 \, m\))}
\]

#### Where:
- **\(F_d\)** : Depth factor = \(1 + 0.33 \left( \frac{D_f}{B} \right)\)
- **\(B\)** : Foundation width, in meters
- **\(S_e\)** : Settlement, in mm

Additional Definitions:
- **\(N_{60}\)** : Standard penetration resistance
- **\(D_f\)** : Depth of foundation

#### Approximation for Large Widths

When the width **\(B\)** is large, the equation can be simplified as follows:

\[
q_{net}(kN/m^2) \approx \frac{N_{60}}{0.08} F_d \left( \frac{S_e}{25} \right)
\]

\[
= \frac{N_{60}}{0.08} \left( 1 + 0.33 \left( \frac{D_f}{B} \right) \right) \left[ \frac{S_e(mm)}{25} \right]
\]

\[
\leq 16.63 N_{60} \left[ \frac{S_e(mm)}{25} \right]
\]

The approximation highlights how the bearing capacity scales with increasing width and settlement conditions of the foundation, allowing for simplification when certain parameters like width become significant.
Transcribed Image Text:### Bearing Capacity of Foundations The following equation is used to determine the net bearing capacity (\(q_{net}\)) of a foundation: \[ q_{net}(kN/m^2) = \frac{N_{60}}{0.08} \left( \frac{B + 0.3}{B} \right)^2 F_d \left( \frac{S_e}{25} \right) \quad \text{(for \(B > 1.22 \, m\))} \] #### Where: - **\(F_d\)** : Depth factor = \(1 + 0.33 \left( \frac{D_f}{B} \right)\) - **\(B\)** : Foundation width, in meters - **\(S_e\)** : Settlement, in mm Additional Definitions: - **\(N_{60}\)** : Standard penetration resistance - **\(D_f\)** : Depth of foundation #### Approximation for Large Widths When the width **\(B\)** is large, the equation can be simplified as follows: \[ q_{net}(kN/m^2) \approx \frac{N_{60}}{0.08} F_d \left( \frac{S_e}{25} \right) \] \[ = \frac{N_{60}}{0.08} \left( 1 + 0.33 \left( \frac{D_f}{B} \right) \right) \left[ \frac{S_e(mm)}{25} \right] \] \[ \leq 16.63 N_{60} \left[ \frac{S_e(mm)}{25} \right] \] The approximation highlights how the bearing capacity scales with increasing width and settlement conditions of the foundation, allowing for simplification when certain parameters like width become significant.
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