Soil Behaviour Type Index

Soil Behaviour Type Index 1

The soil behaviour type index ( $\begin{array}{l}I_c\end{array}$ ) in Soil_Behaviour_Type_Index_1 is defined as:

$\begin{array}{l}I_c=((C_1 - log_{10} Q_t)^2 + (log_{10}F_r+C_2)^2)^{0.5}\\ \ \\ Q_t=\frac{q_c-\sigma_{v0}} {P_a} \left(\frac{P_a} {\sigma'_{v0}}\right)^n\\ \ \\ \left(\frac{P_a}{\sigma'_{v0}}\right) \leq 1.7 \\ \ \\ F_r=\frac{f_s}{q_t-\sigma_{v0}}\times 100 \text {%}\end{array}$

$\begin{array}{l}I_c\end{array}$ is calculated using $\begin{array}{l}n=1\end{array}$ , if $\begin{array}{l}I_c> I_{\text{c break}}\end{array}$ , then it's been accepted, otherwise it's calculated using $\begin{array}{l}n=0.5\end{array}$ . If $\begin{array}{l}I_c< I_{\text{c break}}\end{array}$ break then it's accepted, otherwise it's calculated using $\begin{array}{l}n=0.7\end{array}$ .

Robertson and Wride (1998)

Where:

$\begin{array}{l}C_1\end{array}$ is 3.47 in the published formula, and is stored in the Soil_Behaviour_Type_Index_1_C1 field.
$\begin{array}{l}C_2\end{array}$ is 1.22 in the published formula, and is stored in the Soil_Behaviour_Type_Index_1_C2 field.

The constants are stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

Transition zones

A Trasition Zone in Soil_Behaviour_Type_Index_Transition_1 for a certain depth is considered when:
$\begin{array}{l}2.3< I_c< 2.9\end{array}$ ;
The rate of $\begin{array}{l}I_c\end{array}$ change is rapid (slope of $\begin{array}{l}I_c\end{array}$ vs. depth above and below of the current depth > 5)
and crosses the $\begin{array}{l}I_c=2.6\end{array}$ line.

Soil Behaviour Type Index 2

The soil behaviour type index ( $\begin{array}{l}I_c\end{array}$ ) in Soil_Behaviour_Type_Index_2 is defined as:

$\begin{array}{l}\displaystyle I_c=\sqrt {[C_1-log_{10}Q_t(1-B_q)]^2+[C_2+C_3 \cdot log_{10}F_r]^2}\end{array}$

Jefferies and Davies (1993), NCHRP Synthesis 368 p 27

Where:
$\begin{array}{l}C_1\end{array}$ is 3 in the published formula, and is stored in the Soil_Behaviour_Type_Index_2_C1 field.
$\begin{array}{l}C_2\end{array}$ is 1.5 in the published formula, and is stored in the Soil_Behaviour_Type_Index_2_C2 field.
$\begin{array}{l}C_3\end{array}$ is 1.3 in the published formula, and is stored in the Soil_Behaviour_Type_Index_2_C3 field.

The constants are stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

Soil Behaviour Type Index 3

The non-normalised Soil Behaviour Type Index ( $\begin{array}{l}I_{SBT}\end{array}$ ) in Soil_Behaviour_Type_Index_3 is defined as:

$\begin{array}{l}\displaystyle I_{SBT}= \left(\left(C_1-log \left( \frac{(q_c)}{p_a}\right)\right)^2+(log(R_f)+C_2)^2\right )^{0.5}\end{array}$

Robertson (2010), CPT 10, paper 2-56 (http://www.cpt10.com/PDF_Files/2-56RobSBT.pdf)

Where:
$\begin{array}{l}C_1\end{array}$ is 3.47 in the published formula and is stored in the Soil_Behaviour_Type_Index_3_C1 field.
$\begin{array}{l}q_t\end{array}$ is taken from the Total_Cone_Resistance field on the CPT_DATA table.
$\begin{array}{l}q_c\end{array}$ is taken from the Cone_Resistance field on the CPT_DATA table.
$\begin{array}{l}p_a\end{array}$ is the Atmospheric pressure, 101.4 kPa, and is set in the Formula Tool.
$\begin{array}{l}R_f\end{array}$ is taken from the Friction_Ratio field on the CPT_DATA table.
$\begin{array}{l}C_2\end{array}$ is 1.22 in the published formula and is stored in the Soil_Behaviour_Type_Index_3_C2 field.

The constants are stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

Soil Behaviour Type Index 4

The soil behaviour type index ( $\begin{array}{l}I_c\end{array}$ ) in Soil_Behaviour_Type_Index_4 is defined as:

$\begin{array}{l}\displaystyle I_c=\sqrt {[C_1-log_{10}Q_t(1-B_q)+1]^2+[C_2+C_3 \cdot log_{10}F_r]^2}\end{array}$

Been and Jefferies (1992), Soil liquefaction, a critical state approach, pp. 206-207

Where:
$\begin{array}{l}C_1\end{array}$ is 3 in the published formula, and is stored in the Soil_Behaviour_Type_Index_4_C1 field.
$\begin{array}{l}C_2\end{array}$ is 1.5 in the published formula, and is stored in the Soil_Behaviour_Type_Index_4_C2 field.
$\begin{array}{l}C_3\end{array}$ is 1.3 in the published formula, and is stored in the Soil_Behaviour_Type_Index_4_C3 field.

The constants are stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

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