Evaluation Of Texas Cone Penetrometer Test To Predict Undrained Shear Strength Of Clays

The cone penetration test used in Texas is termed as Texas cone penetrometer (TCP), which works on dynamic principles similar to those of SPT, i.e. a hammer is used to drive the cone device for a preset depth of penetration of 12 inches. Results are typically reported in the form of N12 values. Correlations between N12 and soil strength properties are currently used by the TxDOT to determine in situ strength properties of soils prior to any infrastructure design. \n\t A research study was initiated to evaluate the existing shear strength predicting correlations used by TxDOT and its applicability for soils from various regions of Texas with different geologies and stress histories. Database of TCP and Texas triaxial test results performed over the last ten years by TxDOT in Dallas and Fort Worth districts was compiled to obtain the necessary data for the current research. This thesis research then focused on evaluating the existing correlations and developed improved correlations to predict strength properties of stiff clays from Dallas and Fort Worth regions of Texas. \n\tThe currently used relationship between the penetrometer test N12 value and undrained shear strength was found to be lower bound for the data obtained from Dallas and Fort Worth regions. Hence, improved correlations were established between TCP test results and undrained shear strength for cohesive soils via statistical regression methods. Comparisons of undrained shear strength predicted by these new correlations with both measured strength and predicted undrained shear strength by the current geotechnical manual showed the reliable and improved predictions by the recommended model for stiff clays. These correlations still need to be evaluated with more independent TCP data to further validate their interpretations.