Evolution Mechanism of Interconnected Vertical Fractures in the Overburden of Longwall Coal Mining

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406C431 406 484 370 484 273Z"></path></g><g transform="matrix(.013,0,0,-0.013,32.334,0)"><path d="M531 71V127L115 310L531 494V550L57 335V285L531 71ZM531 -40V10H57V-40H531Z"></path></g><g transform="matrix(.013,0,0,-0.013,43.597,0)"><path d="M384 0V27C293 34 287 42 287 114V635C232 613 172 594 109 583V559L157 557C201 555 205 550 205 499V114C205 42 199 34 109 27V0H384Z"></path></g><g transform="matrix(.013,0,0,-0.013,49.837,0)"><path d="M241 635C89 635 35 457 35 312C35 153 89 -12 240 -12C390 -12 443 166 443 312C443 466 390 635 241 635ZM238 602C329 602 354 454 354 312C354 172 330 22 240 22C152 22 124 173 124 313S148 602 238 602Z"></path></g></svg></span></td></tr><tr><td class="thead-hr" colspan="6"><hr/></td></tr><tr><td class="align_left">Coal (weak)</td><td class="align_center">1.28</td><td class="align_center">1.22</td><td class="align_center">1.17</td><td class="align_center">1.15</td><td class="align_center">1.14</td></tr><tr><td class="align_left">Sandstone (medium hard)</td><td class="align_center">1.2</td><td class="align_center">1.18</td><td class="align_center">1.15</td><td class="align_center">1.13</td><td class="align_center">1.11</td></tr><tr><td class="align_left">Limestone (hard)</td><td class="align_center">1.25</td><td class="align_center">1.21</td><td class="align_center">1.16</td><td class="align_center">1.14</td><td class="align_center">1.12</td></tr><tr class="table-tr"><td colspan="6"><hr class="tbody-hr"/></td></tr></table></td></tr></table>

<div>Coefficient of crushing and swelling of loose rock (coal).</div>

Geofluids

tab4

Table 4

Table 4: Evolution Mechanism of Interconnected Vertical Fractures in the Overburden of Longwall Coal Mining 