Assessment of Excavation Broken Zone around Gateways under Various Geological Conditions: A Case Study in Sichuan Province, China

Abstract

Abstract:To study common failure characteristics of gateways, a total of 55 typical gateways at coal mines, in Sichuan Province, China, were selected for investigating the rules of broken widths based on the ground-penetrating radar (GPR) technique and numerical model. Results indicated that the broken width values around the gateways were larger than 1.5 m, and those in the roof and high side wall were larger than those in the low side wall, as a whole. The width values had close relationships with the thickness of the coal seam and immediate roof, angle of the coal seam, and depth of the gateways. Furthermore, combined with the plastic zone of numerical models in 3-Dimensional Distinct Element Code (3DEC) and the broken width, we obtained the excavation broken zone (EBZ) cross-section diagram for each gateway and determined that the EBZ appeared to have a basically elliptical shape-with the long axis along the seam inclination direction and the short axis along the vertical direction of the rock layer-and that this elliptical shape was only slightly affected by the gateway cross-section shape. It was observed that the failure extent was greater in the seam inclination direction than in the vertical direction of the rock layer. Obviously, the gateways presented asymmetric failure characteristics and implied that an asymmetric support system should be provided when using bolts, cables, and shotcrete combined with steel mesh and steel belts. Such a support system could improve material parameters and form a combined arch structure in surrounding rocks, with arch crown and arch springing thicknesses that are larger in the roof and high side wall.

Archives of Mining Sciences

“…There are 4 main coalfields (1, 2, 3, and 4) in the southwestern part of Sichuan Province, China, as shown in Fig. 1 (Yang et al, 2016b).…”

Experimental investigation on dynamic mechanical properties and fracture evolution behavior of the underground openings with excavation damaged zones

“…(2009) obtained the distributions of EDZ after foundation excavation in Xiaowan dam, China, by the means of borehole camera and classified the excavation damage into excavation heavily disturbed sub-zone (EHDZ) and excavation slightly disturbed sub-zone (ESDZ) according to the damage accumulation curves, showing that the area of ESDZ was larger than that of EHDZ, and the maximum extension lengths of EHDZ and ESDZ are 4.3 m and 11.2 m, respectively. Yang et al. (2016) inverted the EDZ distribution of tunnel excavated in inclined stratum by using geological radar and discrete element program, indicating that damage of the EDZ along the inclined rock stratum was greater than that perpendicular to the rock stratum.…”

Microcrack Evolution and Associated Deformation and Strength Properties of Sandstone Samples Subjected to Various Strain Rates

“…The surrounding rock mass experiences extremely complex stress loading during tunnel development, mining excavation, tunnel support, and goaf backfill. The surrounding rock mass around the working faces is particularly subjected to complex stress loadings during the activities of rock drilling [5,6], rock blasting [7,8], tunnel excavation [9,10], tunnel support [11,12], and rock burst [13].…”