Direct Measurement of CPT Sleeve-Sand Interface Coefficient of Friction

ABSTRACT: The friction between cone penetrometers and soil affects Cone Penetration Test (CPT) tip resistance and sleeve friction. There is evidence in the literature that suggests the value is sensitive to the surface wear condition of the penetrometer and soil type. The interface coefficient of friction is a key input into numerical models of the CPT and may lead to improved interpretation. A friction cell was developed to measure the coefficient of friction between the friction sleeve and soil. Two dry sands were tested in the device and the interface sleeve friction was measured under different normal stresses and densities. Factors affecting the coefficient of friction were discussed along with potential sources of error in the test. The test was shown to be a practical tool for directly measuring interface coefficient of friction and eliminating an important source of uncertainty.