Chamber calibration of CPT under simulated field conditions

Abstract

An important drawback of calibrating CPT in a chamber is its boundary effects. The lateral boundary of the specimen in a conventional calibration chamber is either stress controlled or rigid. Neither of these two boundary conditions can correctly duplicate the field conditions which lies somewhere in between. In order to eliminate the boundary effects, a new calibration chamber system that enables the field conditions be simulated has been developed. The new chamber wall, 800mm in diameter and 1600mm high, is made of 20 vertically stacked steel rings. The boundary movement induced by the cone penetration is measured at each ring level by an extensometer. The lateral stress at each ring level is determined by the stress-strain relationship of the specimen. A series of CPT calibration tests has been performed in a uniform, dry silica sand using the new system. Results show that the new simulator is capable of eliminating boundary effects, even at a relative density of 84%. The paper describes the design of the new chamber system and presents available test data.