Undrained Shear Strength and Consistency Term

Undrained Shear Strength 1

Undrained Shear Strength 1 ( $\begin{array}{l}s_u\end{array}$ ) in Undrained_Shear_Strength_1 is defined as:

When q_t has data,

$\begin{array}{l}\displaystyle s_u = \frac {(q_t - \sigma_{v0})}{N_{kt}}\end{array}$

Otherwise,

$\begin{array}{l}\displaystyle s_u = \frac {(q_c - \sigma_{v0})}{N_{k}}\end{array}$

NCHRP Synthesis 368 p 39

$\begin{array}{l}N_k\end{array}$ N_k and $\begin{array}{l}N_{kt}\end{array}$ are defined on the CPT_POINT_MATERIAL_PROPERTIES, CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables. Different values for $\begin{array}{l}N_k\end{array}$ and $\begin{array}{l}N_{kt}\end{array}$ can be defined for when $\begin{array}{l}q_c\end{array}$ or $\begin{array}{l}q_t\end{array}$ is either greater than or equal to, or less than a defined break point. Each of these tables have six fields from which the $\begin{array}{l}N_k\end{array}$ and $\begin{array}{l}N_{kt}\end{array}$ values, and the $\begin{array}{l}q_c\end{array}$ and qt break point values are stored and retrieved for the calculation of $\begin{array}{l}s_u\end{array}$ _.

Field Name	Description
Undrained_Shear_Strength_1_Nk_qc_BP	Break point used to determine which $\begin{array}{l}N_k\end{array}$ to use in the $\begin{array}{l}s_u\end{array}$ calculation
Undrained_Shear_Strength_1_Nk_qc_LT_BP	Used as the $\begin{array}{l}N_k\end{array}$ in the $\begin{array}{l}s_u\end{array}$ calculation, where $\begin{array}{l}q_t\end{array}$ does not have data, and $\begin{array}{l}q_c\end{array}$ is less than the break point.
Undrained_Shear_Strength_1_Nk_qc_GTE_BP	Used as the $\begin{array}{l}N_k\end{array}$ in the $\begin{array}{l}s_u\end{array}$ calculation, where qt does not have data, and $\begin{array}{l}q_c\end{array}$ is greater than or equal to the break point.
Undrained_Shear_Strength_1_Nkt_qt_BP	Break point used to determine which $\begin{array}{l}N_{kt}\end{array}$ to use in the $\begin{array}{l}s_u\end{array}$ calculation
Undrained_Shear_Strength_1_Nkt_qt_LT_BP	Used as the $\begin{array}{l}N_{kt}\end{array}$ in the $\begin{array}{l}s_u\end{array}$ calculation, where $\begin{array}{l}q_t\end{array}$ has data, and $\begin{array}{l}q_t\end{array}$ is less than the break point.
Undrained_Shear_Strength_1_Nkt_qt_GTE_BP	Used as the $\begin{array}{l}N_{kt}\end{array}$ in the $\begin{array}{l}s_u\end{array}$ calculation, where $\begin{array}{l}q_t\end{array}$ has data, and $\begin{array}{l}q_t\end{array}$ is greater than or equal to the break point.

The fields in the CPT_POINT_MATERIAL_PROPERTIES table allow the $\begin{array}{l}N_k\end{array}$ and $\begin{array}{l}N_{kt}\end{array}$ to be defined for depth ranges for a particular PointID. A top and bottom depth must be specified when using the CPT_POINT_MATERIAL_PROPERTIES table, and the depth ranges must not overlap.

If the CPT_POINT_MATERIAL_PROPERTIES table is populated for the calculated PointID, the $\begin{array}{l}N_k\end{array}$ or $\begin{array}{l}N_{kt}\end{array}$ that lies within the depth range of the current depth of the row in the CPT_DATA table is used to calculate $\begin{array}{l}s_u\end{array}$ . If a matching depth range for the current depth is not found, or $\begin{array}{l}N_k\end{array}$ or $\begin{array}{l}N_{kt}\end{array}$ is missing, then the value is taken from the CPT_POINT_CORRELATION_PARAMETERS or the CPT_PROJECT_CORRELATION_PARAMETERS tables.

Undrained Shear Strength 1 Term

The Undrained_Shear_Strength_Term_1 is defined based on the value of the Undrained_Shear_Strength_1 field and the values in the DG_LOG_CONSISTENCY_DENSITY library table.

Undrained Shear Strength 2

Undrained Shear Strength 2 ( $\begin{array}{l}s_u\end{array}$ ) in Undrained_Shear_Strength_2 is defined as:

When $\begin{array}{l}q_t\end{array}$ has data,

$\begin{array}{l}\displaystyle s_u = \frac {(q_t)}{N_{kt}}\end{array}$

Otherwise,

$\begin{array}{l}\displaystyle s_u = \frac {(q_c - \sigma_{v0})}{N_{kt}}\end{array}$

Where:

$\begin{array}{l}N_{kt}\end{array}$ is stored in the Undrained_Shear_Strength_2_Nkt field.

$\begin{array}{l}N_k\end{array}$ is stored in the Undrained_Shear_Strength_2_Nk field.

The variables are stored on CPT_POINT_MATERIAL_PROPERTIES, CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

The fields in the CPT_POINT_MATERIAL_PROPERTIES table allow the $\begin{array}{l}N_k\end{array}$ and $\begin{array}{l}N_{kt}\end{array}$ to be defined for depth ranges for a particular PointID. A top and bottom depth must be specified when using the CPT_POINT_MATERIAL_PROPERTIES table, and the depth ranges must not overlap.

If the CPT_POINT_MATERIAL_PROPERTIES table is populated for the calculated PointID, the $\begin{array}{l}N_k\end{array}$ or $\begin{array}{l}N_{kt}\end{array}$ that lies within the depth range of the current depth of the row in the CPT_DATA table is used to calculate $\begin{array}{l}s_u\end{array}$ . If a matching depth range for the current depth is not found, or $\begin{array}{l}N_k\end{array}$ or $\begin{array}{l}N_{kt}\end{array}$ is missing, then the value is taken from the CPT_POINT_CORRELATION_PARAMETERS or the CPT_PROJECT_CORRELATION_PARAMETERS tables.

Undrained Shear Strength 2 Term

The Undrained_Shear_Strength_Term_2 is defined based on the value of the Undrained_Shear_Strength_2 field and the values in the DG_LOG_CONSISTENCY_DENSITY library table.

Undrained Shear Strength 3

Undrained Shear Strength 3 ( $\begin{array}{l}s_u\end{array}$ ) based on CSSM in Undrained_Shear_Strength_3 is defined as:

When $\begin{array}{l}q_t\end{array}$ has data,

$\begin{array}{l}s_u = 0.5 \cdot \sin \Phi' \cdot OCR ^\Lambda \cdot \sigma'_{v0}\\\end{array}$

Wroth (1984), NCHRP Synthesis 368 p 39

Where:

_{$\begin{array}{l}\Phi'\end{array}$} is taken from the first of these fields with data: Friction_Angle_3 and Friction_Angle_1
$\begin{array}{l}OCR\end{array}$ is taken from Overconsolidation_Ratio_1
$\begin{array}{l}\Lambda = 1 - \frac{C_s}{C_c}\\\end{array}$ , typically low to medium sensitivity clays are $\begin{array}{l}0.7 \leq \Lambda \leq0.8\end{array}$ , and sensitive and structured clays are $\begin{array}{l}0.9 \leq \Lambda \leq1.0\end{array}$ , and is stored in the Undrained_Shear_Strength_3_Lambda field.

$\begin{array}{l}\Lambda\end{array}$ is stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

Undrained Shear Strength 3 Term

The Undrained_Shear_Strength_Term_3 is defined based on the value of the Undrained_Shear_Strength_3 field and the values similar to that in DG_LOG_CONSISTENCY_DENSITY library table.

Undrained Shear Strength 4

Undrained Shear Strength 4 ( $\begin{array}{l}s_u\end{array}$ ) in Undrained_Shear_Strength_4 is defined as:

$\begin{array}{l}\displaystyle s_u = {C_1} \cdot {\sigma'_p}\end{array}$

Trak et al. (1980), Terzaghi et al. (1996), NCHRP Synthesis 368 p 40

Where:

$\begin{array}{l}\sigma'_p\end{array}$ is taken from Preconsolidation_Stress_1
$\begin{array}{l}C_1\end{array}$ is 0.22 in the published formula, and is stored in the Undrained_Shear_Strength_4_C1 field.
$\begin{array}{l}C_1\end{array}$ is stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

Undrained Shear Strength 4 Term

The Undrained_Shear_Strength_Term_4 is defined based on the value of the Undrained_Shear_Strength_4 field and the values similar to that in DG_LOG_CONSISTENCY_DENSITY library table.

Undrained Shear Strength 5

Undrained Shear Strength 5 ( $\begin{array}{l}s_u\end{array}$ ) in Undrained_Shear_Strength_5 is defined as:

$\begin{array}{l}\displaystyle s_u = \frac {\Delta u}{N_{\Delta u}}\end{array}$

Robertson (2009), pp 28-29

Where:

$\begin{array}{l}\Delta u\end{array}$ is taken from Excess_Pore_Pressure field
$\begin{array}{l}{N_{\Delta u}}\end{array}$ is taken from Undrained_Shear_Strength_5_N field
$\begin{array}{l}{N_{\Delta u}}\end{array}$ is stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

Undrained Shear Strength 5 Term

The Undrained_Shear_Strength_Term_5 is defined based on the value of the Undrained_Shear_Strength_5 field and the values similar to that in DG_LOG_CONSISTENCY_DENSITY library table.

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