Determination of the deformation properties of bedrock under turbine foundations

Summary

This paper presents an improved investigation technique for in-situ determination of the deformation properties of rock masses, which are important parameters in the desing of foundations. This technique permits testing on a circular, one square metre area of the rock. In order to obtain reproducible loading conditions when testing, an equipment was introduced that gave almost uniformly distributed loading of the rock surface. This device is described in this paper. Displacement measurements are made in a central measuring hole, since a point of zero displacement, located equidistant between the loaded surface and the upward-pointing anchoring forces, offered a suitable reference point. In this way, the measuring device is also well protected against disturbing variations in temperature. During cyclic loading and unloading, charateristic load/deflection graphs are recorded, which directly demonstrate the deformation properties of the rock, such as the modulus of deformation at different loads, linearity deviation from linearity, as well as hysteresis effects and creep. It is clear that the results of the investigation apply only to the measuring point—the place at which the investigation was carried out. The properties of the rock nearby may vary considerably. The procedure for using this method of investigation for testing improvement measures for turbine foundations is shown in some examples.