Abstract：Based on fully mechanized mining in slicing, fully mechanized mining with sublevel caving or FMMSC has been developed.With fully mechanized mining in slicing, some large-production coal mines are confronted with problems of FMMSC in lower-slicing while top-slicing of thick seam has been excavated.Behaviors of ground pressure of FMMSC in lower-slicing have some different from that in whole-seam.Owing to expansion factor of re-caving roof-strata being smaller while lower-slicing seam is excavated with FMMSC, the ratio of caved zone height to mining height will increased.Former Basic roof-stratum while top-slicing seam was excavated, has being translated into caved zone and has become upper-immediate roof stratum.So, it is the equilibrium structure with stacked layer of blocks in basic roof with FMMSC in lower-slicing that moves into a higher stratum.Since lump size of upper-immediate roof is large, a semi-arch equilibrium structure of the stratum-rock sometimes can be formed.Periodic destabilization and caving of the structure will lead to a small periodic weighting in coal face.While destabilization and caving of the equilibrium structure with stacked layer of blocks will cause of large periodic weighting.

Keyword：thick seam;fully mechanized mining with sublevel caving;lower-slicing;equilibrium structure;