Effects of Axial Loading Width and Immediate Roof Thickness on the Failure Mechanism of a Notched Roof in Room and Pillar Mining: Experimental Test and Numerical Simulation

The current research scrutinizes the effects of axial loading width and immediate roof thickness on the failure mechanism of a notched roof in room and pillar mining by experimental test and numerical simulation. Gypsum specimens with dimensions of 150 mm × 150 mm × 50 mm containing two rooms and a middle immediate roof (with and without the presence of an edge notch) were prepared for this purpose. The immediate roof has three different thicknesses, i.e., 30 mm, 45 mm, and 60 mm. The length of the edge notches was 1 cm, and their angles were 45°, 90°, and 135°. The upper room was loaded under axial loading with a width of 50 mm. A total of 12 physical specimens were tested. Concurrent with experimental tests, 36 numerical models were simulated. The model geometry was similar to the experimental one, but the upper room was loaded under three different axial loadings, i.e., 10 mm, 30 mm, and 50 mm. The results show that the notch angle, roof thickness, and loading width affect the failure pattern and compressive strength of models. The immediate-edged roof with an angle of 45 has a critical condition compared to other configurations. Also, models under a loading width of 50 mm have less compressive strength compared to other loading widths. The experimental test and numerical simulation show similar outcomes.