R. Bellotti

Uniformity Tests in Calibration Chamber Samples by the Thermal Probe Method

The calibration of geotechnical instruments for in-situ tests, performed on sand samples reconstituted in huge calibration chambers (CC), requires the reproduction of large specimens at given relative densities with good repeatability and satisfactory homogeneity. A test method has been developed with the purpose of evaluating the relative density, DR, in different locations of the CC samples without removing sand. The method is based on experimental correlations between the density and the thermal conductivity of dry sand. The thermal conductivity is determined by small thermal probes, 1 mm in diameter and 70 mm in length, placed in different locations inside the calibration chamber before the pluvial deposition of the specimen. The homogeneity of the specimen is assessed by the local values of DR. A calibration procedure of the thermal probe is proposed that takes into account the effects of stresses on the thermal conductivity of the sand. Examples of uniformity tests performed in ENEL-CRIS and ISMES calibration chambers are presented.