CPeT-IT User's Manual v.3.0

CPeT-IT uses established empirical correlations to estimate geotechnical parameters. Many of them have constants that have a range of values depending on soil type, geologic origin and other factors. The software uses default values that have been selected to provide, in general, conservatively low estimates of the various geotechnical parameters. These default values are assigned to every new CPTU data you import automatically.

The following empirical correlations have been used to calculate parameters:

Input:

•Units for display (Imperial or metric) (atm. pressure, pa = 0.96 tsf or 0.1 MPa)

•Elevation of ground surface (ft or m)

•Depth to water table, zw (ft or m) – input required for each CPT sounding. Equilibrium water pressures are assumed hydrostatic relative to the input GWL

•Net area ratio for cone, a (default to 0.80)

•Relative Density constant, CDr  (default to 350)

•Undrained shear strength cone factor for clays, Nkt (default to 14)

•Over Consolidation ratio number, kocr (default to 0.33)

•Unit weight of water, (default to gw = 62.4 lb/ft³ or 9.81 kN/m³)

•Probe radius (default to 0.0183 m)

 

Output:        

 

In order to view or edit these constants select a CPTU sounding and click on the button located on the Edit CPT File toolbar. The following dialog will appear:

The calculation properties are:

•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 of data.  When either 3 or 5 is selected, the data are averaged every 3 or 5 intervals and presented as a rolling average.

•Ground elevation: Elevation of the free ground surface. This value can be entered for each CPT file or applied to all files.

•GWT: Ground water table below the free ground surface starting from zero value at the surface. For over-water projects, a negative value should be provided to identify that the water level is above the ground surface.  For over-water CPT it is often common that zero load CPT base line measurements are taken at the mudline and in these cases the GWT should be input as zero, since the total weight of the water above the mudline has been removed in the baseline measurements. For over-land projects, this is typically the depth below ground surface.

•Probe radius: Radius of the cone used for the calculation of ch in the dissipation module.

•Cone area ratio: The net area ratio for the cone (default value to 0.85).

•Non-hydrostatic piezom. profile: When checked a custom profile of pore pressure values may be defined and used.

•Cone resistance is corrected: When checked the software will assume that imported raw cone resistance qc is already corrected and equal to qt

•Unit weight of water: Unit weight of water (default value to 9.81 kN/m³ or 62.40 lb/ft³).

•Auto unit weight: When checked the software will use a built-in function to estimate unit weight based on qt and Rf. If unchecked then a list of custom values can be used or apply the constant value entered in the edit box.

•Auto OCR number: When checked the software will try to estimate over consolidation ratio number, kocr for every CPT point. If unchecked then a custom constant value is used (default value to 0.33).

•Auto Nkt: If checked then undrained shear strength cone factor for clays, Nkt will be estimated by the software at every CPT point otherwise a constant value will be applied (default value to 14).

•Dr constant: Relative density constant, CDr (default value to 350).

•Cn cutoff: At very low penetration depths (close to the free ground surface) normalization factor n may take large values resulting to large Qtn values. Enabling this option will set a maximum to the calculate Cn (default value is 2.00)

•Ns: This is a constant used for the calculation of soil sensitivity (ranges between 5.0 to 10.0 with an average value of 7.10)

•Calculate SPT: Selection to choose between the estimation of corrected N60 SPT values or normalized corrected SPT values N1(60)

•Auto transition layer detection: When checked the software will try to detect data that are in transition from either clay to sand or vise-versa. Data belonging to transition zones will not be plotted in the estimations plots and will not contribute to average values used in the Geotechnical Section module. Click on the Tune button to fine tune the detection algorithm.

 

In order to apply any changes made to the selected CPTU just click on the OK button. If you wish the changes made to be the default values for every CPTU that you will create click on the Save as default button. If you click on the Apply to all button, all values entered in this dialog will be applied to every CPTU sounding in the current project. Save coordinates only button will cause the dialog to close applying the changes made to coordinates only.

Closing the above dialog will cause a recalculation of the estimated properties for the selected CPT file.