Constrained Modulus

Constrained Modulus 1

The constrained modulus 1 ( $\begin{array}{l}M\end{array}$ ) in Constrained_Modulus_1 is defined as:

$\begin{array}{l}\displaystyle M=C_1 \cdot(q_t-\sigma_{vo})\end{array}$

Kulhawy and Mayne (1990), NCHRP Synthesis 368 p 33, CPT in Geotechnical Practice p 72

Where:
$\begin{array}{l}C_1\end{array}$ is 8.25 in CPT in Geotechnical Practice, and is stored in the Constrained_Modulus_1_C1 field. NCHRP Synthesis 368 suggest values ranging from 1 to 20, with normal soils approximately 5.

The constant is stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

Constrained Modulus 2

The constrained modulus 2 ( $\begin{array}{l}M\end{array}$ ) in Constrained_Modulus_2 is defined as:

$\begin{array}{l}\displaystyle M=C_1 \cdot G_0\end{array}$

Burns and Mayne (2002), NCHRP Synthesis 368 pp 33-34

Where:
$\begin{array}{l}C_1\end{array}$ is 0.02 for organic plastic clays, up to 2 for over consolidated quartz sands in the published literature, and is stored in the Constrained_Modulus_2_C1 field.
$\begin{array}{l}G_0\end{array}$ is taken from Small_Strain_Shear_Modulus_2.

The constant is stored on CPT_POINT_CORRELATION_PARAMETERS and CPT_PROJECT_CORRELATION_PARAMETERS tables.

This global approach to defining $\begin{array}{l}C_1\end{array}$ is potentially inaccurate, it would be better to define the constant based on soil type with depth.

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