Hydrofracturing A knowledge of the in-situ (primary) stresses in the ground is a prerequisite for the planning of underground structures with a view to their dimensioning and long-term stability. The only method of direct measurement of the in-situ stresses is the method of Hydraulic Fracturing (HF) or the Hydraulic Testing of Pre-Existing Fractures (HTPF). Solexperts together with the daughter company MeSy-Solexperts has many years of experience in hydraulic fracturing in boreholes down to 5 km depth and every commonly used borehole diameters. Besides conventional test execution with the drilling rod or drill string the tests are usually carried out using the in-house developed wireline apparatus.