In-situ stress and rock characterisation via dry reopening test

In the present project a not well-known method has been studied, the dry reopening test DRT. This is a method used to estimate the in-situ stress field of a soil and was. In the context of the project, the test was used to estimate the stress field in the Bedretto underground laboratory in which different experiences related to the geothermic energy are running. The laboratory is placed into an old tunnel, Bedretto tunnel near to the Gothard tunnel. In order to know better the interest of the application of this test a literature review has been done to evaluate the advantages and disadvantages and understand its methodology. To differentiate this method to other methods more often applied in the industry, a few recap of methods that can be applied in the same condition as the DRT is applied in the BUL is done. The DRT estimates the reopen pressure of a pre-existing fracture. To find the in-situ stress field, an adapted version of the Kirsch equation will be applied to find the maximum horizontal stress, which is dependent of the minimum horizontal stress, the pore pressure and the reopen pressure. As the minimum horizontal stress was obtained from a previous test done in the same lab, so a combination of two methods will be necessary to obtain the in-situ stress field. The test was applied in four boreholes, three verticals SB1-1, SB2-1 and SB3-1 and one inclined SB2-2. In the dry reopening test the pressure is injected into a packer which will be in direct contact with the borehole. The principal difference between the hydraulic fracturing test and the DRT is that in this test there is no fluid contact with the borehole. In addition, consider the influence of the packer behaviour an analytical solution was done for this hyperelastic material.