318 2 Challenges in Strong Strata Pressure Control for Thick-Hard Roof Faces 2.1 Geological Conditions of the 10m Large Mining Height Face 2.1.1 Face Overview Caojiatan Coal Mine is located in the Yushen Mining Area, north of Yulin City, Shaanxi Province. The mining area covers about 2735 km² with resource reserves of about 48 billion tons. The current approved capacity has been increased to 25 million t/a. The mine primarily extracts the 2-2 coal seam, mined in eastern and western panels. The face length is 300 m, with an advance length of 5977 m. The seam burial depth ranges from 268 to 356 m, with an extractable thickness of 7.2–12.3 m, averaging 10.5 m. The seam dip angle is 0°– 6°, and the Protodyakonov hardness coefficient is 2–3. 2.1.2 Occurrence Characteristics of Multi-layer Thick-Hard Roofs To fully understand the occurrence state of multi-layer thick-hard roof strata in Caojiatan Coal Mine faces, an underground surrounding rock strength penetration testing device and an electronic borehole camera were used. Twenty-two detection holes were arranged in the auxiliary haulage roadway and return airway to conduct comprehensive testing of the strength and joint/fracture conditions of roof strata within 100 m above the seam. 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 +
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