Texas Cone Penetrometer-Pressuremeter Correlations for Soft Rock

Results from Texas Cone Penetration Tests are employed for assessing the bearing capacity of drilled shafts in relatively soft sedimentary rocks. The test involves driving a solid, nominally 76-mm diameter cone tip into the rock at the bottom of a borehole and recording the number of blows associated with the measured penetration. While the test is common in Texas and Oklahoma, it has many shortcomings due to the dynamic nature of the test and the small penetrations that can occur. Alternatively, the Pressuremeter Test can be employed in test holes within the shale to assess the stress-strain behavior and bearing capacity. While not without limitations, the Pressuremeter Test seems inherently better for assessing bearing capacity of shale, mainly because it involves carefully controlled quasi-static loading of a substantial portion of the formation to failure, resulting in well defined stress-strain behavior. This paper presents results of Texas Cone Penetration and Pressuremeter Tests conducted primarily in Permian age shale and sandstone at nine sites in central Oklahoma. Correlations between results of the two tests and comparisons of predicted end-bearing capacities for drilled shafts are presented and discussed.