Abstract: In order to study the relationship between lithology and its composite structure and deformation and failure depth, based on these comprehensive field test data, restricting function of deformation and failure depth to mining coal seam floor by lithology and its composite structure is discussed. The obvious difference characteristics are obtained on homogeneous floor and soft and hard rock composite structure floor. The study results show as follows：1) The law of deformation and failure of homogeneous floor is relatively simple; the depth of deformation and failure of mining floor is controlled by the strength of floor, and has a gradual characteristics from strong to weak below floor on the whole；2) The deformation and failure floor of soft and hard rock composite structure is complex. There is an obvious restrictive function to the depth of failure floor and deformation degree by the composite structure, weak intercalation being the main weak surface which has strong constraint effect to the depth of failure floor. Namely, soft rock plays an important the effect of the cushion for overlying hard rock, and can produce stress diffusion effect for underlying hard rock. The results show that the floor of lithology and its composite structure has an important restrictive function on the deformation and failure of mining floor depth, and also has theoretical and practical significance to supporting tunnel and preventing water-inrush from mining floor.

Key words: lithology and its composite structure, depth of coal seam floor deformation and failure, comprehensive field test, restricting mechanism