Advanced calibration chambers for cone penetration testing in cohesionless soils

Abstract

The calibration chamber as it was first introduced had its main purpose to calibrate cone penetration test (CPT) in dry, uniformly graded clean sand. The use of an ingenious cavity-wall design enabled the soil specimen be subjected to either a constant stress or zero strain boundary condition. The calibration chamber allowed full scale CPT to be performed in a uniform specimen with known stress and density state. This unique capability was ideal for establishing correlations between CPT and soil design parameters. Empirical rules based on these correlations have routinely been used for the interpretation of CPT in cohesionless soils. The cavity-wall design, with its large but limited specimen, could not properly duplicate the field conditions where soil extends laterally to infinity. CPT performed in the cavity-wall chamber, regardless of the applied boundary conditions, could yield cone tip resistance values that were significantly lower than what would be expected in the field. Much of the calibration chamber related research in the last three decades has evolved around new techniques to either understand or overcome the boundary effects. Various forms of numerical simulations have been implemented and/or coupled into the physical model for CPT calibration. The test material has extended to silty sand under saturated conditions. Centrifuge has also been experimented as an alternative and may be more efficient way to calibrate CPT in coliesionless soils. The paper reviews these various techniques and discusses their implications in the use of calibration test data and future developments in CPT calibration techniques.