Defining CPT and liquefaction calculation parameters

CLiq uses established empirical correlations to estimate geotechnical parameters for basic data interpretation. It also allows the user to modify constants that are essential for the liquefaction calculation procedure. These input parameters are applied to each single CPTU file in the current project, giving the ability to perform analysis with different set of parameters for the various files. In order to preview and/or modify the calculation parameters, first select a CPTU file and then from the Data menu select the Analysis properties command (alternatively you may click on the

button located on the CPT file manager toolbar). The following dialog will appear:

The dialog presents various sections where the user may alter calculation parameters. In more details these section are presented below:

•	Earthquake magnitude: This field holds the earthquake magnitude that will be used for the determination of Magnitude scaling factor. This factor is used to convert the analysis to an equivalent earthquake of a magnitude of 7.50 .

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G.W.T. (insitu): This field holds the absolute depth of water level relative to the ground surface (e.g. a value of 1.00 meter means that ground water level is located one (1) meter below the ground free surface). The value of the insitu G.W.T. will be used for the determination of in-situ stresses needed for the calculation of the basic interpretation and Cyclic Resistance Ratio.

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G.W.T. (earthquake): This field holds the depth of water level during the earthquake and it will be used for the calculation of the Cyclic Stress Ratio (CSR). When a fill is present G.W.T. during earthquake measures from top of the fill. This means that if the insitu G.W.T. is at 2.00 meters and you place a fill of 1.50 meter height then to preserve the G.W.T. during earthquake in the same level you must enter a value of 2.00 + 1.50 = 3.50 meters.

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Display points that do not meet criteria: During the liquefaction assessment calculation the software excludes points by applying a large value (equal to 4.00) on the CRR portion based on some criteria. CSR calculation is normally performed for these points hence they can be plotted in the CSR vs qt1N,cs plot. Unchecking this option will instruct the software not to plot points that belong on a transition layer or measurements above the ground water level that internally are excluded from the liquefaction procedure, hence having a FS value equal to 2.00.

•	X coord. and Y coord.: These fields hold a pair of numbers that represent the coordinates of the CPT. The default value for both fields is 0.000 and can be altered when using the 2D feature. The X, Y coordinates are referenced to some reference point at the site, not latitude or longitude.

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Average interval: Available selection is 1, 3 or 5. The number denotes how many values will be used in order to produce averaged results. If 1 is selected there is no averaging on input data. The function used for averaging data is the simple running average algorithm so there is no volume reduction on the original data.

•	Cone area ratio: The net area ratio for the cone (default value to 0.80). This value is used for the determination of the total cone resistance qt.

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Ic cut-off value: According to Robertson and Wride. (1998) soils with a Soil Behavior Type Index (Ic) greater than 2.60 are characterized as clayey soils. Data points (sounding points) that meet that criterion are excluded from the liquefaction calculation procedure. User may alter this value accordingly to engineering judgment. Default value is 2.60.

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Limit analysis depth at: Experience has shown that the 50-foot (15 m) depth may be adequate for the evaluation of liquefaction potential in most cases, however, there may be situations where this depth may not be sufficiently deep (from SP117). Hence, the software provides a user option to ignore any cyclic liquefaction below a user input depth, where 20 m (or 60 ft) is the default value if the user selects this option (check box checked).

•	Calc. unit weight from SBT: If checked the software will assign a custom unit weight based on the SBT classification. If not checked then it is assumed that the soil has a constant unit weight over depth, equal to the value entered in the Default gamma value field.

•	Auto transition layer detection: If checked the software will try to locate and eliminate (exclude from liquefaction calculation) points that belong to transition layers. Detailed information on this procedure can be found here.

In this section the user may specify final site conditions that is condition of the site during the earthquake.

•	Same as initial: Select this option if the final site conditions (conditions during earthquake) are the same as the initial conditions (when CPT was performed.

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Has a fill: Select this option if the final site conditions where changed by applying a fill. The Height of fill input box holds the value of the height of fill and the Fill unit weight input box should hold the unit weight of the material used to construct the fill. These two parameters will be used to calculate the geostatic stresses during earthquake.

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Is excavated: Select this option if there will be an excavation during the earthquake. CLiq will not perform CSR calculations from depth 0.00 down to the value entered at the Depth field while CRR will be given a large value of 4.00. The Width field is the width of the foundation (foundation is assumed to be of a rectangular shape) and the L/B input box hold the value of the length to width ratio of the footing (e.g. a value of 1.00 means the footing is square and a value of 10 means that the footing is strip). Calculations of the load stresses distribution below the footing are performed based on the Boussinesq theory for a point under the middle of the footing. If the Rigid footing is checked the formula for a rigid footing will be used.

As noted above, data points are characterized as clay-like based on their corresponding Ic value. By default the software will assume that clay-like points are not susceptible to cyclic liquefaction and remove these points from the calculation (this is done by setting a high value to CRR component of that point). CLiq advances in this section by presenting more options on how the software will treat clay-like data points. In brief, these options are:

•	Assume not susceptible to liquefaction: This is the default option and instructs the software not to include in the liquefaction calculation procedure points with Ic value greater than the cut-off value specified.

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Clay-like materials behaviour: Based on the recent publication from Boulanger and Idriss (2007) clay-like points will be included in the liquefaction calculation procedure but the CRR7.50 component will be determined based on the estimated in-situ undrained strength. Undrained strength is determined using the CPT readings for that point and a user input value for the cone factor Nkt (default value is 14). For the estimation of vertical settlements and lateral displacements, the software provides user input values for the maximum post-earthquake volumetric strain, ev and maximum post-earthquake shear strain, γ (default values of ev = 0.50% and γ=15%).

In this section, the user may modify properties regarding the estimation of lateral displacements.

•	Gently slope ground: This is the default selection. Lateral displacements will be performed based on the slope value entered (value must be larger than 0.20% and smaller than 3.50%).

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Level ground with free face: When checked the software will estimate lateral displacements based on the geometry profile specified. L field holds the horizontal distance of the CPT from the slope toe, and H field holds the vertical height of the slope. When the Ignore displacements below 2H check box is checked, calculation of the estimated lateral displacements will not be performed for points that lay below a depth of 2xH from the ground surface (minus the fill height if specified).

If you need to set these parameters to all CPTU files in the current project, click on the Apply to all button (this will result the dialog to close and CLiq will recalculate all CPTU files). When done click on the OK button to close the dialog. Please notice that the software will try to automatically recalculate the selected CPTU file and will prompt for an answer:

Answer Yes to the above dialog if you must recalculate the basic interpretation of the CPTU file e.g. if you have altered the cone area ratio or the thin layer detection algorithm. If you answer No the software will use the current interpretation to perform the liquefaction calculation. If you are not sure about your answer always click on the Yes button. If your answer is Cancel then no calculation will be performed but the changes made to the liquefaction calculation properties will not be lost.