Weak Rock (Custom)
The custom weak rock model is intended for cases where site-specific test data or local correlations are available, allowing the designer to override the default theoretical formulas with project-specific parameters.
Shaft Friction in Custom Weak Rock
The shaft friction is estimated using a user-defined correlation constant:
\[
q_s = C \cdot \sigma_{c}^{0.5}
\label{eq:unit-shaft-resistance-wrc}
\]
where \(C\) is the correlation constant, a value between 0 and 1 determined from site-specific data or local practice, and \(\sigma_c\) is the uniaxial compressive strength of the rock in MPa.
General notes for shaft friction in custom weak rock
- The correlation constant \(C\) should be selected based on local experience, back-analysis of pile load tests, or published correlations for similar rock types.
- Ultimate unit skin friction \(q_s\) has a limiting value of 10000 kPa or 1450 psi.
Tip Resistance in Custom Weak Rock
The unit tip resistance is directly specified by the user as an input parameter, bypassing the theoretical formula used in the standard Weak Rock model.
This approach is particularly useful when:
- Full-scale pile load test data is available for the project site.
- Local practice or building codes prescribe specific tip resistance values for the rock formation.
- The designer has reason to believe the theoretical correlation does not adequately represent the site conditions.
General notes for tip resistance in custom weak rock
- Ultimate unit tip resistance \(q_b\) has a limiting value of 50000 kPa or 7250 psi.