Education Rock Mechanics Robert Hack

These lectures concern the basics in rock mechanics, mechanical behavior of intact rock, strength and deformation of intact rock.

Rock mechanics for engineering geology and civil engineering purposes is mostly governed by discontinuities in the rock mass. Discontinuities are planes of mechanical weakness, such as fractures, joints, faults, etc. The discontinuities make the behavior of a rock mass anisotropic and make calculations of strength and deformation highly complicated. The chemical and physical exposure of rocks to water and air at the surface of the earth reduce rocks to soil, a process normally denoted as weathering. Soil in various states of weathering may form layers or pockets that exist within rock masses or form the boundary of a rock mass. These soils often contain remnants of discontinuities which were originally present in the rock mass and hence cause an anisotropic behavior of soil masses. An engineering application, such as a tunnel, foundation or slope, in a rock mass is highly likely not only to be in rock but also in soil. Therefore the study of discontinuous rock mechanics is not complete without including discontinuous soil masses.

The lectures on discontinuous rock mechanics discuss discontinuities and the mechanical behavior of rock and soil masses including discontinuities. An extensive discussion of rock mass (or soil mass) classification systems is included as these are presently the most commonly used tools for design of engineering applications in rock mechanics. Numerical calculation methods are briefly described and its advantages or disadvantages in comparison with classification systems. Civil engineering applications are used to illustrate what consequences can be expected of a civil engineering use of the rock mass and what mechanisms govern the interaction between the rock or soil mass and the civil engineering application. The type and possibilities of how an excavation can be made with what type of excavation machine and what the influence is on the rock mass is extensively described. Remedial measures, as tunnel support, slope anchors, etc., to stabilize underground excavations in rock or soil masses are also described. Large scale anchoring

Large scale anchoring of the foundations for the abutment of a bridge. Only the anchors plates (small black squares) can be seen on top of reinforced concrete beams (after Geoconsult, Salzburg, 1978)