Abstract: Focusing on widely distributed sandy mudstones above upper No.2-2 coal seam in Gaojialiang mine, Ordos, the microscopic structure and mineral composition of sandy mudstones deposited during different periods were tested, and the fractured zones above working faces with different geological conditions were further detected. The results show that particle volume of sandy mudstone in Jurassic Zhiluo and diazepam group is small, with the characteristics of point contact between particles, low voidage, high content of montmorillonite, swelling with water, poor cementation, easy broken, and water preventing ability after rock fractured. Evaluation model of water-preserved mining in shallow seam with the sandy mudstone roof was constructed, two basic conditions of water preserved mining were obtained, and the evaluation method was put forward. Industrial test shows that the evaluation results are concordance with that of field practice.

Key words: shallow buried coal seam, sandy mudstone, water preserved mining, fracture zone, evaluation