Felsmasse

Felsmasse is a term used in geology and geotechnical engineering to describe the in-situ rock mass that forms the structural basis for engineering works. It encompasses the intact rock material as well as the discontinuities that cut through it, such as joints, faults, bedding planes, and foliation. The concept emphasizes that the mechanical behavior of rock is controlled not only by mineral composition but also by the geometry and condition of its fractures.

Key properties of a Felsmasse include the rock type and mineralogy, the compressive strength of the intact rock, and the characteristics of discontinuities—spacing, persistence, orientation, roughness, and the presence of infill material or water. Weathering, pore water pressure, and in-situ stress also influence how the rock mass responds to loads. The overall quality is often summarized by classification systems such as the Rock Mass Rating (RMR) or the Q-system, which combine several attributes into a single parameter used for design decisions.

Assessment of a Felsmasse relies on field mapping, borehole logging, core analysis, and sometimes geophysical methods. Data on discontinuity orientation and block size distribution can be analyzed with stereonet techniques to evaluate stability and failure modes. The concept is central to projects in tunneling, underground construction, slope engineering, and foundations, guiding decisions on excavation methods and support measures (such as bolts, shotcrete, drainage, or underpinning).

In practice, the Felsmasse is a dynamic property, varying with depth, weathering, and loading, and it requires site-specific evaluation to ensure safe and economical design.