(1.State Key Laboratory of Mining Disaster Prevention and Control，Shandong University of Science and Technology，Qingdao ，China；2.Mining Engineering National Experimental Teaching Demonstration Center，Qingdao ，China)

In order to study the bearing capacity of the underlying gravel in the gob under various conditions, the fracture deformation test of the fractured sandstone was carried out by using the fractured rock deformation-seepage testsystem. The effects of particle size, gradation combination, saturated state and loading mode on the deformation characteristics of fractured sandstone were analyzed. Research results indicate that the stress-strain relationship of fractured sandstone is closely related to particle size, gradation combination, saturated state and loading mode, and the stress-strain relationship of different particle size can be expressed by exponential function. Under the action of stress, the strain of the large-size group of gravel increases rapidly; with the increase of the gradation index n, the content of large-size gravel in the graded gravel group increases, and the strain value at the end of the test stress loading increases accordingly; the strain increment of the same grade of gravel under the same stress is obviously greater than that of the gravel strain in the dry state. The saturated water load reduces the bearing capacity of the fractured sandstone by nearly 14%; under cyclic loading and unloading the gravel stress- strain relationship can still be expressed by an exponential function, and the final value of the gravel strain under cyclic loading and unloading is about 1.25 times the final value of the continuously loaded crushed stone. The study provides theoretical guidance for surface settlement and surrounding rock deformation control in gob.

国家重点研发计划资助项目(2018YFC0604702)；国家自然科学基金资助项目(51509149，51379119，51774199)；山东省重点研发计划资助项目(2018GSF120009)