This study presents experimental results of the mechanical characterization of artificial rock joints constructed by 3D-printing with the perspective of being used in 3D physical models of underground excavations in rock masses. The presence of fractures in rock mass controls its mechanical behavior, and physical modelling is a technique used to understand this behavior at a reduced scale. The use of 3D-printing technology in physical modelling allows a strict control of the joint's geometry (roughness, number of rock bridges, etc.). In this study the 3D-printing technology used is the selective laser sintering, and the material is Polyamide 12. Geometric characterization shows that 3D-printing gives a high precision in dimensions with details less than 0.4 mm. Shear tests results show a reproduction of mechanical behavior of joints. A failure criterion is proposed to take into consideration the influence of the number of rock bridges and the roughness over the mechanical properties.

1 Introduction

Understanding rock mass behavior is essential as the number of projects related to mining engineering, underground excavations and rock slope stability is continuously increasing (Jiang et al., 2016). Rock mass behavior influences the design and the cost of the excavated structures in rock mass, but also the monitoring of the structures behavior while being exploited, and the associated risks. However, rock masses are heterogeneous and thus complex objects for which the behavior is controlled both by the rock matrix and by the presence of fractures of various scale (Brady & Brown, 2004).

The mechanical behavior of rock masses may be studied with in-situ experimentation and numerical or physical modeling (Ghabraie et al., 2015). Physical modeling is an experimental technique to simulate and reproduce engineering problems at a reduced scale using an analogue material and adhering to scaling laws. The main difficulties of building a physical model of rock masses lie in at least two areas: how to explicitly reproduce the complex geometry of a fractured rock mass in a physical model, and how to control the mechanical properties of both the matrix and each joint in the rock mass according to scaling laws? Depending on the fracture network, two modeling strategies may be chosen. The first considers a continuous equivalent media using in general geomaterials, after applying homogeneous methods (Lin et al., 2015; Pouya & Ghoreychi, 2001). The second considers a discontinuous media by simulating stratifications or by building the rock mass by an assembly of blocs (Fuenkajorn & Phueakphum, 2010; He et al., 2010). These models are necessarily a simplification of the reality and have difficulty reflecting the actual behavior of a rock mass because they do not represent the complex geometry of rock joints networks, and because they do not control the joints mechanical properties. The investigation of a new method, based on the 3D-printing technology (3DP), is then the main objective of this study.

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