Compressibility-Based Interpretation of Cone Penetrometer Calibration Chamber Tests and Corresponding Boundary Effects

Calibration chambers have been used to calibrate in situ testing devices (e.g., standard penetration test, cone penetration test, and flat plate dilatometer) in laboratory settings. Researchers have long suggested, however, that penetration resistance measured in a calibration chamber differs from what would be measured under similar conditions in the free field due to the finite chamber size and chamber boundary conditions. Using a database of 847 cone penetration tests performed in sand-filled calibration chambers, this paper reexamines assumptions used to interpret tests and boundary effects, analyzes the efficacy of published calibration chamber correction factors, and provides a novel framework for interpreting calibration chamber data based on soil compressibility. This study suggests that (1) trends in cone tip resistance are relatively unaffected by boundary effects; (2) factors used to correct calibration chamber cone tip resistance to an equivalent free-field value only marginally improved the correlations/trends; and (3) cone tip resistance is similar for soils of equally similar compressibility, density, and effective confining stress. The authors suggest that calibration chamber data may not require corrections for chamber size or boundary conditions so long as a ratio of chamber diameter to cone penetrometer diameter of 20 is satisfied.