A stress calculation model for the 3D borehole slotter

A stress calculation model is proposed for a new stress measurement device called the 3D borehole slotter. This instrument allows the calculation of t he 3D in situ stress tensor in a single borehole without the need for a dri ll on the site at the time of the measurement and without bonding strain ga uges at the borehole wall. The 3D borehole slotter requires cutting half mo on shaped slots with different orientations at a borehole wall using a smal l diamond impregnated blade and monitoring the strains which are relieved n ormal to the slot. This paper shows that combining six slots cut on the bor ehole wall with one to three slots cut parallel to the borehole axis and fi ve to three cut with a 45 degrees angle, allows the calculation of the in s itu stress tensor. The optimal slot combination is determined and 3D finite element analyses are used to evaluate the degree of stress relief normal t o the slot at the strain sensor location and also to estimate the strains i nduced parallel to the slot by this local stress relief. The results obtain ed from these analyses are then used directly in the stress calculation mod el. (C) 1999 Elsevier Science Ltd. All rights reserved.