The Influence of JRC and Surface Geometry on the Mechanical/Hydraulic Aperture of 3D Printed Joints
Tan-Minh LE1+, Jia-Jyun DONG2#
1Rock and Soil Mechanics Laboratory, Graduate Institute of Applied Geology, National Central University, Taiwan, 2Graduate Institute of Applied Geology, National Central University, Taiwan

Characterizing rock joints' hydro-mechanical behavior is critical for rock engineering because joints frequently act as weak planes and fluid paths of the rock masses. Among others, joint roughness directly controls the mechanical and hydraulic behaviors of rock joints. The Joint Roughness Coefficient (JRC) has been widely used to quantify the joint roughness for four decades. This parameter was incorporated into empirical equations to predict the joint closure under stresses and fluid flow characteristics as well. However, the validity of using one single parameter to represent the complex geometry of joint surface could be an interesting topic to be explored. This study creates numerous smooth joint samples (including matched and mismatched joints) with similar JRC (2-4) but different surface geometry via 3D printers. The mechanical and hydraulic apertures (E and e) of the printed joint samples under different normal stress were measured using high confining stress, permeability/porosity measurement system (YOKO2). The relation between joint closure (related to E) and fluid flow characteristics (related to e) can be quantified. The testing results show a significant influence of joint surface geometry on the E-e relation; even the JRC is roughly the same. The role of geometry heterogeneity of real rock joint surface on the hydro-mechanical coupling needs further study.