Influence of folds and fold-related faults on slope stability

Geological structures such as folds have a significant influence on the behaviour and stability of slopes, foundations and tunnels in hard rock (Badger 2002). Although the importance of structural geology for geotechnical buildings has long been recognized, in practice it is often not consistently taken into account in all project phases.

In geotechnical models, discontinuities such as joints, schistosity and bedding planes, as well as faults, are usually represented as flat surfaces. Nevertheless, this simplification only corresponds to reality to a limited extent: discontinuities are often corrugated, and the location of folds and fold-related joints can significantly influence the stability of slopes. However, more recent approaches also integrate fold geometries (Fereshtenejad, Afshari et al. 2016, Erharter 2024) to realistically capture their influence on slope stability.

Variations in the position of folds can promote different failure mechanisms, while certain fold orientations can have a stabilizing effect.

Against this background, the following key question arises: To what extent is it permissible to simplify surfaces to flat surfaces, and how can folds be realistically represented in numerical models?

To determine the discontinuity system (fracture network) and the relevant structural parameters, the rock outcrops to be investigated are surveyed using UAV flights. The photogrammetric images obtained are processed using special software such as Agisoft Metashape, and high-resolution textured terrain models are derived from them. These serve as the basis for stereographic analyses, geotechnical evaluations and the calculation of discrete fracture networks.

In addition, the effects of the spatial location of the fold and joint systems on the stability of the surveyed rock surfaces are investigated using the discrete element method (Particle Flow Code; Itasca). The discrete fracture networks derived from UAV photogrammetry are integrated into the models and the spatial location of the slope (exposed rock surface) is varied. In this way, the influence of the fold position on the stability of the rock faces under investigation is systematically examined.

The results should reveal systematic relationships between fold geometry, joint distribution and slope stability, improve understanding of structurally induced instabilities and support the further development of geotechnical assessment methods in rock mechanics.