To determine the capacity of rock-socketed piles, especially socketed in weathered rocks, which fall under Method-2 of IRC 78, the shear strength values of rock are required to be derived based on SPT N values. During the Geotechnical Investigation, the SPT N values for the weathered rock strata are generally reported as refusal or reported as SPT N/penetration. As the mobilization of end bearing in rock-socketed piles is fully dependent on the quality of concrete formation at toe, the skin friction is the most reliable component for rock-socketed piles, especially in weathered rocks. To determine the skin friction, estimation of unit skin friction of the regional rocks in which the piles are socketed is important. The ongoing Chennai metro rail Phase II Project has almost 120 km long route length, out of which the elevated stretch is nearly 76 km long in which the piers are resting on Pile foundations. From this Project, the pile load test data such as compression load test using O-cell method, pull-out test, and high strain dynamic test are used. PLAXIS-3D is used for the back analysis of the load test results as most of the load tests did not reach the pile ultimate failure state. A generalized relationship is determined from the back analysis to estimate the unit skin friction mobilized in rock strata, especially in weathered granitic rocks of Chennai region.