We study the structural instability mechanism and effect of a multi-echelon support in very-deep roadways. We conduct a scale model test for analysing the structural failure mechanism and the effect of multi-echelon support of roadways under high horizontal stress. Mechanical bearing structures are classified according to their secondary stress distribution and the strength degradatio... https://www.roneverhart.com/5-15P-ANGLE-PLUG-B-W-HUBBELL-HBL5266CA/