Dynamic Cone Penetrometer and California Bearing Ratio Correlation for Andean Volcanic Subgrades: Local Calibration Study and Application to Mountain Road Design in Southern Colombia

Abstract

Adequate geotechnical characterization of subgrade bearing capacity on secondary and tertiary mountain roads represents an ongoing challenge in resource-limited contexts, where the cost and logistical complexity associated with conventional in situ California Bearing Ratio (CBR) testing significantly restrict the number of characterization points. This work documents the calibration and statistical validation of an empirical correlation between the dynamic cone penetration index (PDC INV-172) obtained through an 8-kilogram dynamic cone penetrometer and in situ CBR values measured according to Colombian technical standards (INV E-169), specifically developed for silty-sandy volcanic soils in the Andean Nariño region. Through execution of 18 paired tests along the road sections Pasto-Jongovito and Pasto-Obonuco (approximately 4 km), a dynamic penetration index range between 5.40 and 61.00 mm/blow was identified, correlated with undisturbed CBR values ranging from 3.40% to 49.27%. Application of logarithmic regression analysis transformed the relationship into a power-law model of the form CBR = 381.2 × (PDC)−1.05 with Pearson correlation coefficient r = 0.953 and coefficient of determination R² = 0.908, statistically significant at the 5% confidence level using Student's t-test. The model adequately captures the nonlinear behavior between dynamic penetration resistance and bearing capacity, positioning within the upper performance range relative to international correlations reported in the literature. Furthermore, implementation of PDC equipment augments subsurface characterization capacity, strengthening research infrastructure and academic training in Andean pavement geotechnics. The results support PDC as an efficient tool for rapid subgrade evaluation during prefeasibility phases, preliminary design, and quality control of flexible pavements on mountain corridors.