<< Click to Display Table of Contents >> Navigation:  Geotech > Functions > Geotechnical Function – EQUIS.GEOTECH_CPT_DATA

Purpose

 

The EQUIS.GEOTECH_CPT_DATA function queries the raw Cone Penetration Test (CPT) data parameters stored in DT_DOWNHOLE_POINT_DATA to calculate several correlated CPT parameters. The EQUIS.GEOTECH_CPT_DATA function creates a function report called Geotechnical CPT Data. It is also used in the Geotechnical CPT Parameters and Geotechnical CPT Parameters Export reports.

 

 

Calculation Details

 

The function calculates the parameters based on the unit defined in DT_TASK_PARAMETER.PARAM_VALUE for DT_TASK_PARAMETER.PARAM_CODE = ‘cpt_output_units’. The PARAM_VALUE must be either ‘E’ for English or ‘M’ for Metric. If the value is empty, then the function will calculate the results in English units. The function checks the PARAM_UNIT associated with the raw CPT parameter and converts the values accordingly. The function only supports converting values if the stored units are MPa, KPa, or TSF.

 

The ‘pressure_unit’ field included in the output applies to all reported fields that have ‘TSF/MPa’ listed in the Unit column in function output table provided later in the article. The ‘unit_weight_unit’ field applies to the ‘unit_weight’ field included in the output.

 

 

It is required that the CPT location have a depth value present in the DT_WATER_TABLE table where DT_WATER_TABLE.TYPE = ‘CPT’. In addition, the following CPT input parameters (stored in the DT_DOWNHOLE_POINT_DATA table) are required for the function to compute:

•Depth (DT_DOWNHOLE_POINT_DATA.DEPTH)

•Cone Resistance (DT_DOWNHOLE_POINT_DATA where PARAM_CODE = ‘cpt_cone_resist’)

•Friction Resistance (Sleeve Friction) (DT_DOWNHOLE_POINT_DATA where PARAM_CODE = ‘cpt_friction_resist’)

•Pore Pressure (DT_DOWNHOLE_POINT_DATA where PARAM_CODE = ‘cpt_pp_u2’)

 

The DT_DOWNHOLE_POINT_DATA.REPORTABLE_YN value must be either ‘Y’ or empty for the function to report the CPT reading. If DT_DOWNHOLE_POINT_DATA.REPORTABLE_YN = ‘N’, then the record will be excluded from the function output.

 

 

CPT Probe ID

 

When available, the function uses the Net Area Ratio value associated with the Probe ID used.

 

The CPT net area ratio is used in calculating the following parameters:  

•Corrected Tip Resistance (qt)

•Friction Ratio (Fr)

•Unit weight

 

The function checks the PARAM_VALUE for the DT_LOCATION_PARAMETER.PARAM_CODE = ‘probe_id’ associated with the location. It then searches for the DT_EQUIPMENT_PARAMETER.PARAM_CODE = 'cpt_net_area_ratio' where DT_EQUIPMENT_PARAMETER.EQUIPMENT_CODE = DT_LOCATION_PARAMETER.PARAM_VALUE for DT_LOCATION_PARAMETER.PARAM_CODE = ‘probe_id’. If there are multiple ‘cpt_net_area_ratio’ values for the PROBE ID, then the function grabs the value with the latest MEASUREMENT_DATE.

 

If the Probe ID does not have an associated ‘cpt_net_area_ratio’ record in the DT_EQUIPMENT table, then the function uses a default net area ratio of 0.8. The function also checks for an invalid net area ratio value where the cpt_net_area_ratio < 0.2 or cpt_net_area_ratio > 1. If the value is invalid, then the function uses 0.8.

 

 

CPT Cone Factor (CPT Nkt)

 

The function checks for the CPT Nkt value in DT_TASK_PARAMETER.PARAM_CODE = ‘cpt_nkt’. If this value is empty, then function assumes the CPT Nkt value to be 14.

 

The CPT Nkt value is used in calculating the following parameters:  

•Undrained Shear Strength (Su)

•Sensitivity (St)

 

 

EQUIS.GEOTECH_IC_QTN

 

The EQUIS.GEOTECH_CPT_DATA function references another scalar-valued function: EQUIS.GEOTECH_IC_QTN.

 

The EQUIS.GEOTECH_IC_QTN function calculates the Normalized Cone Resistance (Qtn) and Soil Behavior Type Index (Ic) parameters by using the iterative stress exponent method based on Robertson 2014 CPT Guide.

 

 

EQUIS.GEOTECH_NSBT

 

The EQUIS.GEOTECH_CPT_DATA function references another scalar-valued function: EQUIS.GEOTECH_NSBT

 

The EQUIS.GEOTECH_NSBT function determines the Normalized Soil Behavior Type (SBTn). The appropriate SBT zones are determined by using the Normalized Cone Resistance, Qtn, and the Friction Ratio, Fr. The zone boundaries are defined by overlaying a graph in Excel on the graphic of Robertson’s updated 2009 SBTn chart.

 

 

Function Outputs – CPT Parameters

 

The following table lists the CPT parameters that the EQUIS.GEOTECH_CPT_DATA function outputs, including function field name, associated unit, and equation used (when applicable).