Comparison between a New Rigid Dilatometer and the Ménard Pressuremeter in a Reconstituted Sand

Borehole expansion tests such as the Ménard pressuremeter test (PMT) are widely used in geotechnical testing as they provide a modulus that can be used to estimate settlements under geotechnical structures. This paper describes a new soil investigation apparatus that performs an expansion test in a prebored hole called the dilatometer Fondasol test (DFT). From this test, an in situ load-displacement curve is obtained in the same manner as the PMT. The apparatus is based on the concept of the rigid dilatometer used in rock mechanics with two rigid and semicylindrical shells spread against the borehole walls. Four different prototypes have been developed and successfully tested on Hostun sand reconstituted by vibration in a test chamber at a density index varying from 0.18 to 0.72. Results show that despite the significant differences in the shells’ geometry, they have little impact on the measurement of an apparent modulus. Three different formulas derived from elastic theory have been evaluated for the computation of dilatometer moduli: EDFT;M, EDFT;G, and EDFT;BJ. A comparative study with pressuremeter tests shows that EDFT;M and EDFT;BJ are close to the pressuremeter moduli EPMT;M with a ratio EPMT/EDFT ranging between 1.2 and 0.8 depending on the density of the sand. The moduli EDFT;G are significantly higher than EPMT;M and vary importantly depending on the prototypes. Dilatometer’s load-displacement curves show that global failure occurs at higher stresses than with the pressuremeter.