Quantifying the anisotropy of bearing capacity in jointed rock masses with orthogonal joint sets: an experimental and mechanistic evaluation

The bearing capacity of jointed rock masses is inherently anisotropic due to joint geometry. This study investigates the influence of orthogonal joint-set orientation on the ultimate bearing capacity and failure mechanisms of shallow foundations under plane-strain conditions. A testing programme using plaster of Paris as a rock-analog material evaluated three orthogonal joint configurations: 0°–90°, 45°–45°, and 30°–60°. Results indicate that the 0°–90° configuration exhibited the highest bearing capacity with predominant intact crushing; the 45°–45° case showed intermediate capacity with block cracking and sliding; and the 30°–60° configuration produced the lowest capacity, governed by sliding along the critical joint. A mechanistic analysis based on stress transformation was conducted to interpret the observed failure modes, leading to a dimensionless relationship linking joint orientation to sliding instability. The results confirm the pronounced influence of joint orientation on bearing capacity and failure mode, underscoring the experimentally quantified anisotropy of jointed rock masses.