Effect of Boundary Conditions on CPT Calibration Chamber Tests

Abstract

Calibration chambers are employed to reproduce field conditions in laboratory cone penetration tests (CPTs). However, their measurements are often affected by the limited size of the calibration chamber and the imposed boundary condition. Hence, the chamber size effect needs to be considered in predicting field performance or verifying and establishing new correlations between cone resistance and soil properties from CPT calibration chamber results. The effect of chamber boundary condition is examined in this study through both numerical simulations and laboratory CPT calibration chamber tests. For this purpose, a series of discrete-element simulations were performed and compared with experimental calibration chamber tests to investigate the influence of the boundary condition on cone tip (qc) and sleeve frictional (fs) resistances. The numerical simulations were further used to study the effects of particle size, sample height, relative density, and effective overburden pressure on qc and boundary effects. The results indicated that qc in calibration chamber tests on loose to medium-dense sands and those carried out with a rigid boundary would be closer to the field condition and would require little compensation for the limited effect of chamber size. Based on these findings, specific correction factors are proposed to better estimate the free field penetration resistances.