OFFICIAL Figure 3 – The distribution of fractures in cross-section. The strata with different fracturing behaviours are highlighted by dashed eclipse (Duan et al., 2025a). 2.4. Borehole imaging while drilling for geotechnical structures Several geo-sensing technologies show strong potential for detecting structural features in rock masses to support geotechnical design. For fractures intersecting drill holes, traditional tools such as optical televiewers (OTV) and acoustic televiewers (ATV) remain the most effective. However, identifying fractures that do not intersect boreholes (particularly those sub-parallel to drilling) requires alternative approaches. Borehole radar (BHR) offers advanced capabilities for subsurface characterisation in mining and quarrying. Forward-looking BHR can predict coal seam tops by detecting intersections of direct and reflected signals before the drill bit reaches the seam, enabling proactive drilling decisions (Zhou & van de Werken, 2015; Zhou et al., 2020). Side-looking BHR configurations allow detection of poorly sampled sub-vertical fractures and bedding planes, which are critical for geotechnical assessment and rock quality evaluation (Zhou et al., 2021). Figure 4 illustrates a radar profile from a borehole filled with highly conductive water, showing distinct V-shaped borehole-guided events (BGEs). Events with opposite-phase reflections indicate lithologic boundaries, while same-phase reflections signify fractures. Blasthole radar systems, using larger drill rods (~200 mm), can enable real-time look-ahead via 5 GHz Wi-Fi. In contrast, slim-hole BHR tools (~40 mm) cannot support Wi-Fi during drilling and require internal data logging for post-survey
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