Rigidity Index

Rigidity Index 1

Rigidity index 1 ( $\begin{array}{l}I_r\end{array}$ ) for fine material is recorded in the Rigidity_Index_1 is defined as:

$\begin{array}{l}\displaystyle I_r=exp \left [ \left(\frac{C_1}{M}+C_2 \right) \cdot \left ( \frac{q_t- \sigma_{v0}} {q_t-u_2} \right) -C_3 \right]\end{array}$

Mayne (2001), NCHRP Synthesis 368 p 46

Where:
$\begin{array}{l}C_1\end{array}$ is 1.5 in the published formula, and is stored in the Rigidity_Index_1_C1 field.
$\begin{array}{l}C_2\end{array}$ is 2.925 in the published formula, and is stored in the Rigidity_Index_1_C2 field.
$\begin{array}{l}C_3\end{array}$ is 2.925 in the published formula, and is stored in the Rigidity_Index_1_C3 field.
$\begin{array}{l}M\end{array}$ is the Cam clay constant, slope of the critical state line and is defined as:

$\begin{array}{l}\displaystyle M= \frac{6 \cdot sin \Phi'}{3- sin \Phi'}\end{array}$

$\begin{array}{l}\Phi'\end{array}$ for the calculation of the Cam clay constant M is taken from the Friction_Angle_1 field on the CPT_DATA table.

The constants are stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

This correlation of $\begin{array}{l}I_r\end{array}$ is calculated only when the Soil_Type_1 field value on the CPT_DATA table has a value of Fine for that row.

Rigidity Index 2

Rigidity index 2 ( $\begin{array}{l}I_r\end{array}$ ) for fine material based on plasticity index and OCR is recorded in the Rigidity_Index_2 is defined as:

$\begin{array}{l}\displaystyle I_r= \frac{exp[C_1 \cdot(C_2-PI)]}{[1+ln\{1+C_3 \cdot(OCR-1)^{C_4}\}]^{C_5}}\end{array}$

Keaveny and Mitchel (1986), NCHRP Synthesis 368 p 46

Where:
$\begin{array}{l}C_1\end{array}$ is 0.0435 in the published formula, and is stored in the Rigidity_Index_2_C1 field.
$\begin{array}{l}C_2\end{array}$ is 137 in the published formula, and is stored in the Rigidity_Index_2_C2 field.
$\begin{array}{l}C_3\end{array}$ is 0.385 in the published formula, and is stored in the Rigidity_Index_2_C3 field.
$\begin{array}{l}C_4\end{array}$ is 3.2 in the published formula, and is stored in the Rigidity_Index_2_C4 field.
$\begin{array}{l}C_5\end{array}$ is 0.8 in the published formula, and is stored in the Rigidity_Index_2_C5 field.
$\begin{array}{l}PI\end{array}$ is the Plasticity Index, and is stored in the Plasticity_Index field.
$\begin{array}{l}OCR\end{array}$ is taken from the Overconsolidation_Ratio_4 field on the CPT_DATA table.

The constants are stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

This correlation of $\begin{array}{l}I_r\end{array}$ is calculated only when the Soil_Type_1 field value on the CPT_DATA table has a value of Fine for that row.

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