Correlation of Texas Cone Penetrometer N-values with undrained shear strength of low plasticity clay

In foundation design, shear strength plays a significant role. Determination of in-situ shear strength of soil is both laborious and costly. Several methods can determine shear strength of soils, and the Texas Cone Penetrometer (TCP) test is one such method generally used by geotechnical engineers in Texas. To determine the shear strength of soil, TCP tests use previously developed correlation equations between TCP blow count and shear strength. The accuracy of these correlated results plays a significant role. Many geotechnical engineers in Texas feel that the use of this test to determine the strength parameters may result in unsafe design of structures. This study attempted to verify the correlation between soil strength parameter cohesion and the Texas Cone Penetrometer values based on bearing capacity theory, available test data, and results of the finite element analysis. The study determined the relations between depth (at which the test is conducted) with other soil parameters such as natural moisture content, plastic limit, liquid limit, and unit weight of soil.; The field study includes collection of field and lab tests conducted by the Texas Department of Transportation (TxDOT) Beaumont District. The collected data were rerecorded, filtered, and analyzed using the computer software, Minitab. Finite element analysis was used to study the displacement of the cone at three different levels of depth with five different consistencies. A correlation between soil shear strength and TCP blow count was derived based on the determined cone displacement for particular soil strength. The study also developed a new correlation with consideration of the depth factor based on the data collected and bearing capacity theory. Unconfined compression and classification tests were conducted to compare the correlated results.; The study developed relations between depth and other soil parameters such as natural moisture content, plastic limit, liquid limit, and unit weight of soil. Conducted tests showed a good agreement between these developed relations. The research evaluated the new correlations derived between the shear strength and TCP blow count for low plasticity clay with the one currently used by TxDOT. The results of the evaluation conclude that the current relation used by TxDOT may result in an unsafe design. Furthermore, the depth factor, which is not considered in the current TxDOT correlation, plays an essential role in the relationship between the soil shear strength and blow count. Newly-developed correlations based on the bearing capacity theory and finite element method can be good replacements for the current correlation used by TxDOT.