Single-borehole measuring method for broken rock zone in gently inclined thin layer weakness structure

Abstract

According to the structural characteristics of gently inclined thin layer rock mass in which lots of weak interlayer existed, the concept of gently inclined thin layer weakness structure was proposed. If single-borehole measuring method of the acoustic along the conventional arrangement mode was used in measuring the broken rock zone in this structure, the change of the relationship curves (Vp-L) between acoustic p-wave velocity (Vp) and borehole depth (L) would present the irregular feature due to the mechanical characteristics of layered rock mass and harmful effects of weak interlayers, and the scope of broken rock zone couldn’t be defined quickly. Based on the analysis of the mechanical characteristics of layered rock mass, the propagation rule of acoustic and distributions characteristics of plastic zone and slip zone in layered rock mass, new arrangement mode of acoustic measuring boreholes for broken rock zone in gently inclined thin layer weakness structure was proposed. Namely, the measuring boreholes in two sides were parallel to the strata, the measuring boreholes in the roof and floor perpendicular to the strata. Besides the controlling depth of the measuring boreholes in the scope of the large plastic zones or the large slip zones should be increased. Engineering example showed that new acoustic measuring boreholes arrangement mode had the better applicability and could determine the scope of the broken rock zone in the gently inclined thin layer weakness structure quickly.