The mechanical model of thick wall cylinder was introduced to study on water inrush from karstic collapse column′s side wall.Coal pillar of collapse column′s side wall was regarded as porous medium.Mohr Coulomb strength theory and elastoplastic mechanical model were used to deduce the analytic expression of the coal pillar elastoplastic stress state

and the relational expression between the radius of plastic zone and the water pressure

while the critical water pressure of water inrush of subsided column side wall was calculated by the trial and error of programme.Based on this

the influence of coal pillar′s porosity

coal pillar′s shear strength parameters

and coal pillar′s width on critical water pressure were analyzed.The results show that:（1）the values of the critical water pressure decreases with increase of the values of coal pillar′s porosity.So the result irrespective of seepage action is on the side of safety when the coal pillar fracture development;（2）The bigger of coal pillar′s width

the higher of coal pillar′s shear strength parameters

the lower possibility of water inrush from collapse column′s side wall will occur.The coal pillar can be injected into the cement slurry to reduce its porosity and improve its strength based on the above results.This approach can effectively prevent water inrush from collapse column′s side wall

and also can reduce the coal pillar′s width.Therefore

it has important significance to reduce the coal loss.