Fastening in Rock Mass-Structural Design of Shallow Embedded Anchors in Inhomogeneous Substrate

Unlike traditional base materials such as concrete or masonry, there are no guidelines for rock as a base material for post-installed anchors. The varying rock properties (e.g., rock type, discontinuities) and numerous installation parameters (e.g., embedment depth, anchor diameter) leave engineers with limited information on design resistances, leading to an uncertain basis for anchor applications in rock. To identify the key parameters that determine rock as a base material, an evaluation of rock characteristics was conducted, combined with in situ pull-out tests in different key geologies (granite, limestone, mica schist, dolomite, granulite) and discrete element modeling, which has been found to be suitable for investigating the load-bearing behavior of post-installed anchors in rock. Discontinuities were identified as the main factor influencing the load-bearing capacity of post-installed anchors in rock mass. Based on the in situ investigations, assessment methods for rock as a base material were proposed, along with corresponding resistance partial safety factors for design of 2.5, 2.0, and 1.7 for high, medium, and low levels of uncertainty regarding possible inhomogeneities. A limit value R ≥ 36, associated with rebound hammer assessments, was defined for the low degree of uncertainty, showing limitations for schistose rock. This is concluded by a design approach for determining design resistances of shallow fasteners in rock mass.