The effects of staggered and non-staggered joints on the ultimate bearing capacity, load settlement behavior, and failure mechanism with the change of excavation depths

Extensive research is available on excavation walls in soils. However, very few studies address their performance in rocks and jointed rock masses. This study aimed to investigate the effect of staggered and non-staggered joints on ultimate bearing capacity, load settlement behavior, failure mechanism, and lateral wall displacement for a jointed rock mass supported by an excavation wall. The present study has been conducted on scaled 2D physical laboratory model tests. Tests were performed on artificial jointed rock masses comprising orthogonal joint sets and an excavation wall supporting a nearby foundation. Two sets of rock masses were prepared, one with continuous joints and another with slightly staggered joints. Three different excavation depths were used in this study. The results revealed that minor staggering significantly enhanced bearing capacity by two to three times compared to continuous joints. Furthermore, the presence of minor staggering reduced both vertical settlement of the footing and lateral movement of the excavation wall, thereby altering the failure patterns. Additionally, a discrete element model (DEM) was developed using the Universal Distinct Element Code (UDEC) to compare numerical simulation results with the physical model test results. The discrepancies between the numerical and physical model results were attributed to the difficulty in accurately representing the physical position of individual blocks in the UDEC model. This issue was addressed by introducing the concept of “apparent cohesion” and aligning DEM results closely with experimental outcomes, confirming the effectiveness of this approach in reconciling numerical and physical model differences. • The study presents 2D-scaled physical model tests on continuous and slightly staggered orthogonal joints. • The article discusses jointed rock mechanics in excavation walls focusing on foundation-bearing capacity and wall deformation. • The different failure mechanisms of orthogonal joints are reported. • A theoretical "Apparent Cohesion" concept is proposed in DEM to handle staggering effects that are difficult to model otherwise.