DCIP tomografi för kartläggning av jorddjup och strukturer i berg

There are plans to build an energy storage in the rock at Onneslov near Dalby in Skane. The bedrock is of a part of Romeleasen and mainly comprises gneiss, with elements of amphibolite and dolerite intrusions. The area is located immediately south of the Sydsten’s large rock quarry, which shows that the rock is mostly heavily fractured with clay weathered zones of different sizes. In connection with underground construction fractured zones and weathering constitutes a risk for problems with water inflow and stability. Furthermore, variations in depth to the upper surface of the rock can lead to stability problems in the upper portions of a planned construction.Electric resistivity tomography (ERT) is now an established pre-investigation method for tunnel projects, and it has been used on a large scale in connection with for example the Hallandsas Tunnel. The method provides continuous models of variations in the electrical properties of the rock in two (2D) and three dimensions (3D) that can be linked to variations in the rock mechanical and hydraulic properties. ERT measured by a combination of DC resistivity and induced polarization can be called DCIP tomography, which can provide additional information about the variation in the material properties of the rock. With the help of new and improved methods of data acquisition, processing and interpretation it is possible to collect large amounts of good quality IP data in a time and cost effective way, paving the way for better and more nuanced models of the rock and variations in its properties. The newly developed technology has been tested in full scale at Onneslov. Three parallel DCIP sections about 1 km long, with a maximum survey depth of about 170 m were measured, plus a 800 m long cross-section. Furthermore, DCIP logging was carried out in two percussion drill holes down to 200 m depth in which it is furthermore made logging of diameter, natural gamma radiation, seismic velocity and flow rate during pumping.Geological interpretation of the DCIP results agree well with what one can expect from the documentation of soil depth, and variation in degree of fracturing and weathering as documented from drilling. A major advantage is continuous models that can be linked to variation in soil depth, structures in the rock and hydrogeological conditions. The combined surveys with surface-based measurements and borehole measurements are complementary and provide a more reliable overall picture of the variations in rock conditions.