Improved interpretation of the pressuremeter test by taking into account the deformation of the membrane.

A mathematical model of pressuremeter membrane is presented. It allows to take into account the influence of the shape and the thickness of the membrane, on the pressuremeter results. The pressuremeter allows to measure a pressuremeter modulus and a limit pressure, which are used to estimate the bearing capacity of the foundation. It is assumed in the different standards (AFNOR, NF EN ISO 22476-4 Essai pressiométrique Ménard. AFNOR, Reconnaissance et essais géotechniques, 2012; ASTM, Standard test method for prebored pressuremeter testing in sols, ASTM D 4719-87. ASTM, 1994) that there are only two corrections which should be applied to the measurements, one on the dilatation of the equipment and one on the membrane rigidity. This approach assumes that the pressure applied into the probe is equal to the reaction pressure of the soil at the borehole wall outside the probe. This neglects on the one hand the effect of the thickness of the membrane and on the other hand the influence of the deformation of the membrane which takes place under free or fixed boundary conditions. To solve this scientific obstacle we use the theory of beams with Wrinckler's hypothesis on the response of the soil to the deformation of the probe. We present two new corrections of the pressuremeter measurements, which allows to approach the effective reaction of the soil around the pressuremeter. A theoretical correction is proposed and checked by the numerical results of a finite element calculation of the probe expansion which takes into account the presence of two types of membrane: one with free ends and the other with embedded boundaries. An application is carried out on the Fondasol measurements performed on the Messanges site for Arscop (Nouvelles Approches de Reconnaissance des Sols et de Conception des Ouvrages géotechniques, 2016) research program with 5 different probes and 3 different boring techniques. The influence of the thickness of the membrane should be taken into account to improve the precision of the pressuremeter results (pressuremeter modulus, limit pressure). [ABSTRACT FROM AUTHOR]