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Rock (Tomlinson)

The Tomlinson method for rock-socketed piles incorporates the Rock Quality Designation (RQD) to account for the discontinuity structure of the rock mass. This method is based on Tomlinson and Woodward (2015), pp. 192-200.

Shaft Friction in Rock (Tomlinson Method)

The shaft friction along the pile socket in rock is estimated by:

\[ q_s = \alpha \cdot \beta \cdot \sigma_{c} \label{eq:unit-shaft-resistance-rt} \]

where:

  • \(\alpha\) is the socket reduction factor
  • \(\beta\) is the socket correction factor
  • \(\sigma_c\) is the uniaxial compressive strength

Socket Reduction Factor

The socket reduction factor is:

\[ \alpha = \min\left( 0.5 \cdot \sigma_{c}^{-0.5},\ 1.0 \right) \label{eq:socket-reduction-factor} \]

where \(\sigma_c\) is in MPa. This is the same adhesion factor used in the Weak Rock model.

Mass Factor

The mass factor \(j\) is interpolated from the Rock Quality Designation (RQD):

Table 2: Mass factor vs. RQD, after Tomlinson and Woodward (2015).

\(\text{RQD}\) (%) 50 75 90 100
\(j\) 0.2 0.5 0.8 1.0

For intermediate values, linear interpolation is used.

Socket Correction Factor

The socket correction factor \(\beta\) is interpolated from the mass factor \(j\):

Table 3: Socket correction factor vs. mass factor, after Tomlinson and Woodward (2015).

\(j\) 0 0.015 0.055 0.14 0.2 0.4 0.6 0.8 1.0
\(\beta\) 0.35 0.4 0.5 0.6 0.655 0.775 0.865 0.935 1.0

For intermediate values, linear interpolation is used.

General notes for shaft friction in rock (Tomlinson method)

  • Reference for equations \((\ref{eq:unit-shaft-resistance-rt})\), \((\ref{eq:socket-reduction-factor})\), and Tables 2 and 3: Tomlinson and Woodward (2015), pp. 192-200.
  • Ultimate unit skin friction \(q_s\) has a limiting value of 10000 kPa or 1450 psi.

Tip Resistance in Rock (Tomlinson Method)

The tip resistance uses the same empirical formula as the standard Weak Rock model:

\[ q_b = 4.83 \cdot \sigma_{c}^{0.51} \label{eq:unit-tip-resistance-rt} \]

where \(\sigma_c\) is the uniaxial compressive strength in MPa.

General notes for tip resistance in rock (Tomlinson method)

  • Reference for equation \((\ref{eq:unit-tip-resistance-rt})\): Zhang (2004), p. 219.
  • Ultimate unit tip resistance \(q_b\) has a limiting value of 50000 kPa or 7250 psi.