When the instability of a coal pillar causes the roof of a room-and-pillar mined-out area to deform but does not collapse,the surface undergoes a significant deformation,posing a threat to the safety of ground buildings and structures.The development mechanism of deformation in the overlying strata of the mined-out area under this condition was studied using physical simulation and theoretical analysis.The research showed that the maximum deformation point of the surface after the instability of the coal pillar in the mined-out area was corresponding to the position of the initial unstable coal pillar and the crack on the mined-out area roof in the vertical direction.When the roof of the mined-out area was deformed but did not collapse,the overlying rock deformation could be divided into three areas:the"strip shaped","ladder shaped",and"funnel shaped"deformation area.The loose layer deformed into a"funnel shaped"development.Before the roof of the mined-out area ruptured,it could be regarded as a fixed beam model under a uniform load.Under the condition of instability of the coal pillar,vertical cracks would occur in the tensile stress zone of the lower surface of the rock beam span and propagate vertically upwards.The continuous instability of the coal pillar would cause damage to the rock beam along the weak surface of the original crack,ultimately leading to a tensile fracture of the rock beam.When the deformation of the bedrock developed to the interface,the loose layer would gradually undergo a slip tension shear failure,ultimately forming a"funnel shaped"failure form.
room-and-pillarmined-out areainstability of coal pillarphysical modeling
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