A Numerical Study of Chamber Size and Boundary Effects on CPT Tip Resistance in NC Sand

A numerical modeling procedure was used to quantify calibration chamber size and boundary effects for cone penetration testing in sand. In the numerical analyses, chamber diameter and boundary conditions were varied to investigate the effects of chamber size and boundary conditions on cone tip resistance. These analyses show that, for loose sand, a chamber-tocone diameter ratio of 33 is sufficient for the boundaries to have no influence on the cone tip measurements. However, for very dense sand, the numerical analyses show that the chamberto- cone diameter ratio should be more than 100 to ensure that boundaries have no influence on cone tip measurements. Numerical analysis indicates that, not only the sand relative density but its stress state is also a significant factor in influencing the chamber size effects. The results of the numerical analyses were compared to existing empirically based relationships. Suggestions are provided to reduce the effects of chamber size and boundaries on cone tip resistance measurements in sand.