Abstract: Aiming at the key problem of optimal size design of coal pillar in shallow and extra thick coal seam，taking a fully mechanized caving face of a coal mine in Xinjiang as an engineering example， the reasonable determination of coal pillar width in working face is systematically analyzed by means of physical experiment，theoretical derivation and numerical simulation. Through mechanical tests，the ten⁃ sile strength of coal is 0.69~0.82 MPa，and the compressive strength is 4.84~5.44 MPa，indicating that the mechanical properties of coal pillars are relatively weak. Based on the limit equilibrium theory and Mohr�Coulomb criterion，the vertical stress distribution model of coal pillar is established，and the reasonable coal pillar width is 19.04 m by theoretical calculation. Numerical simulation is used to further analyze the mining response characteristics of coal pillars under the condition of 14~24 m width. The results show that when the width of coal pillar increases to 19 m，the stress concentration of coal pillar is significantly allevi⁃ ated，and a stable elastic core area is gradually formed inside，and the overall mechanical state tends to be stable. At the same time，the control effect of surrounding rock deformation in the lower section of roadway is effectively improved. The comprehensive analysis results show that when the width of coal pillar is 19 m， it can effectively maintain the stability of roadway surrounding rock during mining. The research conclu⁃ sions can provide theoretical support and practical guidance for the width design of coal pillar in shallow buried extra-thick coal seam under similar geological conditions.

Key words: shallow buried extra thick coal seam, coal pillar width, numerical simulation, ultimate bal? ance theory, Mohr-Colomb criterion