Cracking Behaviour of Mineralised Fractures Under Direct-Shear
Authors: Kong Lie , Shang Junlong 
Published: August 2024

ABSTRACT:
Mineral-filled fractures (rock veins) are common in the Earth's upper crust. Understanding the cracking and deformation behaviour of the mineral-filled fractures is of fundamental value for wide applications such as earthquakes, landslides, and the stability of underground infrastructure. In this study, we simulated the cracking behaviour of mineralised fractures under a direct-shear load using the discrete element method (DEM). A synthetic rectangular numerical specimen sized 5 cm by 5 cm was considered. An analogous vein was embedded along the middle line of the specimen. We calibrated the mechanical properties of the vein and host rock materials based on the experimental tests of a veined rock from the Cornwall area in England, UK which is a potential area for constructing the geological disposal facility (GDF) for nuclear waste. We analysed results including cracking dynamics, loading curves, and crack partitions in/along different material phases (i.e., host material, vein, and host-vein interface). We envisage that this study could provide valuable information regarding the activation and deformation of mineralized fractures especially from a micro-scale perspective.

1. INTRODUCTION
The mineral vein (mineral-filled fracture) is a unique geological structure that widely exists in geoformations. Generally, the mineral veins are created within the pre-existing fractures that were earlier formed by geo-stresses and crustal movement. The existence of fractures in the geo formations is very important for wide geoengineering and geomechanical applications such as safety and stability of underground construction, and prediction of earthquakes and landslides. In the literature, many works have investigated the effect of fractures or weak interfaces on the mechanical and hydromechanical behaviours of rock formations [1-6]. Consensus has been reached that the fracture is critical in geomechanics because it often dominates the mechanical and hydro-mechanical behaviour of rock.
However, in the current geomechanics and rock mechanics studies, the fracture is often considered as a linear interface. The presence of mineral veins in fractures was often ignored or less investigated. While is revealed that the existence of the mineral vein will alter the mechanical and hydraulic properties of the host rock by changing the mechanical properties (strength, modulus, friction etc) and hydraulic properties (void/apertures, etc) of the host fractures [7], how the mineral veins affect the activation and deformation behaviours of pre-existing fracture is still unclear. It is important to understand the activation and deformation of the mineralised fractures which is fundamentally important for rock and geological engineering projects. The knowledge obtained through the proposed works is beneficial because it will allow us to make use of the mechanisms that could contribute to techniques that could either improve efficiency (e.g., enhancing the stability) or migrate the unwanted risks (e.g. severe collapse/leakage of tunnels and caverns).