1557 Figure 1 In-situ test of roof strata strength Figure 2 Borehole camera view of roof strata 1) Strata Strength. Figure 1 shows the roof strata strength distribution at chainage 6000 m in the auxiliary haulage roadway. Within 100 m above the seam, there are multiple thick-hard roof layers. Specifically, at 11.8 m above the seam, there is a 14.1 m thick fine sandstone layer with an average uniaxial compressive strength (UCS) of 69.1 MPa, reaching nearly 100 MPa at maximum. At 35.6 m above the seam, there is a 14.2 m thick interbedded siltstone/fine sandstone layer with an average UCS of 58.8 MPa. At 59.7 m above the seam, there is a 13.7 m thick interbedded siltstone/fine sandstone layer with an average UCS of 59.8 MPa. At 78.7 m above the seam, there is a 10.1 m thick medium-grained sandstone layer with an average UCS of 68.3 MPa. 2) Strata Structure. Within 100 m above the seam, there exist multiple hard rock layers/groups with thicknesses of 10–33 m. The roof strata overall exhibit a distinct "high + medium + low position thick-hard roof" distribution pattern, and the thickness of hard layers varies significantly along the face advance direction, as shown in the borehole camera images. The strata above the face have good integrity; the roof is dense and hard with few joints/fractures, and interlayer fractures are not obvious. Apart from weak planes at 0–15 m, 56.5 m, and 64.5 m above the roof, the remaining intervals consist of intact, dense, and hard rock. 2.2 Technical Challenges The mining characteristics of the 10m ultra-large mining height fully mechanized face—including the ultra-large excavation space, ultra-high coal rib, and ultra-high coal flow—determine that the face will face a series of world-class challenges in surrounding rock control, key equipment, and intelligent synergistic control. Although the mining depth in the Yushen Mining Area is not great, the high face production coupled with multiple thick-hard roof layers above the seam leads to intense strata pressure behavior and severe hydraulic support damage. Practices in 6.0 m ultra-large mining height faces in this area showed that during initial mining, large-area roof hanging occurred, with first weighting spans exceeding 150 m and dynamic load coefficients during periodic weighting exceeding 1.5, accompanied by support leg retractions of 0.4– 1.0 m. Under high-intensity mining in a 10m ultra-large mining height face, the large single-pass excavation space makes the scale effect of face surrounding rock control more prominent. Controlling strong strata pressure and rib spalling/caving becomes a critical challenge that must be overcome. 2.3 Solution Pathway To address the surrounding rock control challenges in 10m ultra-large mining height faces, a synergistic control strategy of "active powerful support protection + regional fracturing destressing and weakening" is proposed for controlling strong strata pressure in ultra-large excavation spaces and stabilizing ultra-high coal ribs. While employing ultra-high resistance hydraulic supports for powerful support, underground long horizontal borehole fracturing technology is used to weaken and destress thick-hard strata. Underground long horizontal borehole hydraulic fracturing primarily actively weakens and destresses medium- and low-position thick-hard strata (10–60 m above the roof), reducing the layered thickness, breakage block size, and hanging span of the thick-hard roof. It increases the bulking factor and filling degree
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