Abstract: Similar material simulation test has been applied to research the motion of overlying strata and the characteristics of fracture development of steep-inclined extra-thick coal seam mining by horizontal section top coal caving. The proportion of coal seam has been chosen as cement∶sand∶water∶ activated carbon∶coal=6∶6∶7∶1.1∶79.9 by low strength mechanical test and orthogonal test with the density of 0.913 g/cm 3 and uniaxial compressive strength of 0.076 MPa. The result of similar material simulation test has shown that 1) The overlying strata caving occurs as an integrity only after two or three mining levels have been mined; 2) The overlying strata of shallow mining levels move coordinately before caving; 3) In the deep mining level, hinge structure is formed between adjacent mining levels; 4) When the mining activity goes deeper, roof gets completely destroyed and caved after each mining level is mined; 5) The characteristics of abscission layer and fracture development are consistent with the motion of overlying strata; the depth of pressure relief is about 15 m.

Key words: steep-inclined very thick coal seam, similar material simulation test, proportioning test, overlying strata movement, pressure relief of floor