Approach for Estimating Effective Friction Angle from Cone Penetration Test in Unsaturated Residual Soils

This paper proposes approaches to estimate effective friction angle from cone tip resistance with incorporation of matric suction. Cone penetration tests (CPTs) are performed in unsaturated residual soil layers, where matric suction is measured with depth. Unsaturated triaxial testing is performed on retrieved samples adjacent to the CPT soundings. In addition, the proposed model incorporates a more robust stress state through the use of coefficient of earth pressure at rest (K-0) and overconsolidation ratio (OCR). Results indicate that reducing the CPT tip resistance data without incorporating the matric suction effect leads to 6-9 degrees overestimations of the friction angle (the matric suction was approximately 80-90 kPa in type MH soil). The incorporation of a more representative stress state using the mean effective stress in the CPT data reduction leads to a 2-3 degrees reduction of the estimated friction angle compared with traditional approaches for OCR values equal to or greater than 2. (C) 2017 American Society of Civil Engineers.