Reliability Analysis of Cone Penetration Test Measurements in Calculating Undrained Shear Strength of Soil

The Cone Penetration Test (CPT) is widely used in Louisiana to classify soils, measure undrained shear strength (Su), and identify bearing stratum for driven piles. This paper compares the values of Su based on CPT measurement with Su of the unconfined compression test. A total of 752 CPT soundings were collected and archived using ArcGIS software in which 503 were matched with adjacent boreholes and 249 did not have adjacent borehole data available. From these CPT locations, 862 unique Su strength data points were obtained at various depths. The dataset was analyzed for general as well as specific trends in order to identify appropriate parameters to be included in the study. Soil classification was clearly the most plausible parameter based on which the CPT undrained shear strength estimates should be calibrated. The calibration of the CPT expression for Su was conducted using the First Order Reliability Method (FORM) and accounting for all sources of uncertainty. Optimum CPT coefficient values to calculated Su were computed for various target reliability values.