Study on the Modification of Confining Rock for Protecting Coal Roadways against Impact Loads from a Roof Stratum

Promoting the ability of anti-bursting of the confining rock of a coal roadway is of significant importance to the safe production of a coal mine. In particular, in deep-buried coal mines, highly frequent rock burst occurs due to large earth pressure and complex geological conditions, which needs serious improvement. This paper investigated a type of confining rock modified method, which can modify the physical properties of the surrounding rock and form a crack region and a reinforced region by blasting and grouting reinforcement. Based on a set of physical model experiments and numerical modeling, the results of a comparative analysis between a normal roadway and the modified roadway in the static stress redistribution, dynamic stress, damage evolution, and energy dissipation suggest that the modified confining rock is capable of protecting the coal roadway against rock burst from roof stratum, obviously reducing and transferring the concentered static–dynamic stress out of the cracked region, dissipating the dynamic energy by plastic damage in the cracked region, and keeping the integrity of the reinforced region. In addition, the velocity of the dynamic stress vibration wave at the surface of the modified coal roadway is obviously reduced, which is beneficial for decreasing the movement of cracked rock blocks and protecting the lives and goods in the coal roadway.

A Coal Burst Mitigation Strategy for Tailgate during Deep Mining of Inclined Longwall Top Coal Caving Panels at Huafeng Coal Mine

A coal burst mitigation strategy for tailgate in mining of deep inclined longwall panels with top coal caving at Huafeng Coal Mine is presented in this paper. Field data showed that coal bursts, rib sloughing or slabbing, large convergence, and so forth frequently occurred within the tailgate entries during development and panel retreating employing standard longwall top coal caving (LTCC) layout which resulted in fatal injuries and tremendous profit loss. The contributing factors leading to coal bursts were analyzed. Laboratory tests, in situ measurement, and field observation demonstrate that the intrinsic bursting proneness of the coal seam and immediate roof stratum, deep cover, overlying ultrathick (500–800 m) conglomerate strata, faults, and, most importantly, improper panel layout led to coal bursts. By employing a new strategy, that is, longwall mining with split-level gateroads (LMSG), gateroads on either end of a LMSG panel are located at different levels within a coal seam, adjacent LMSG panels overlap end to end, and the tailgate of the adjacent new LMSG panel can be located below the headgate entry of the previous LMSG panel or may be offset horizontally with respect to it. Numerical modeling was carried out to investigate the stress distribution and yield zone development within surrounding rock mass which was validated by field investigation. The results indicate that standard LTCC system gave rise to high ground pressure around tailgate entries next to the gob, while LMSG tailgate entry below the gob edge was in a destressed environment. Therefore, coal bursts are significantly mitigated. Field practice of LMSG at Huafeng Coal Mine demonstrates how the new strategy effectively dealt with coal burst problems in mining of deep inclined longwall panels with a reduced incidence of ground control problems. The new strategy can potentially be applied in similar settings.

Study on Zoning of Overburden Strata and Roadway Deformation of Ascending Mining in Thin Coal Seam

In order to solve the problems appeared in mining process of upper seam in Xiaohezui coal mine, a technical scheme of ascending mining was put forward. UDEC, a discrete element numerical simulation soft was used to study the characteristics of zoning of overburden strata and the rule of vertical stress distribution of the upper coal, the results show that the upper coal is on the top of the equilibrium belt without step dislocation, the structure of roof stratum and floor stratum stay complete with slight separations, so ascending mining is feasible; the range of the upper coal influenced by the stoping of below working face is -85m~65m, the vertical stress reaches a maximum 15m ahead the below working face, and reaches a minimum behind it 25m. It is applied in the engineering practice, the roadway deformation discipline of the upper coal is similar to the distribution rule of vertical stress, provides a theoretical basis for guiding and improving the roadway support of ascending mining.

Buckling and Post-Buckling Behavior for Roof Strata in Longwall Mining

In accordance with the occurrence behavior of roof strata and the fracture characteristics of key stratum in shallow seam longwall mining, this paper studied the post-buckling behaviors of key roof stratum in the process of mining by using initial post-buckling theory, which derived a critical load and a breaking span of the main roof during the first weighting, determined the final subsidence for broken key stratum, and presented an application with the example of Daliuta 1203 face. The results indicate that the rock blocks a in are state of non-equilibrium after main roof breaking, the equilibrium path of main roof is unstable from breaking to final subsidence; thick unconsolidated layers above roof have effect on post-buckling behaviors of key stratum; the stability for bifurcation point equilibrium configuration and post-buckling equilibrium path of roof strata could be revealed and an effective method for determining displacement field of imperfection structure could be provided by using initial post -buckling theory.