Experimental study on combined load-bearing instability of filling body and roadway surrounding rock in original roadway filling without coal pillar excavation

Under the influence of deep high ground stress and strong mining, stress of surrounding rock of gob-side entry increases. The original roadway filling without coal pillar excavation is proposed to cope with the difficult problem of surrounding rock control in deep roadway. In the technology, filling body and surrounding rock form a variety of combined structures, and these structures stability is closely related to roadway control. In this paper, theoretical analysis and mechanical test are used to analyze the strength characteristics of single lithology and bearing capacity deterioration characteristics of multi-lithology combination. The results show that the long-term strength of filling body is greatly affected by water-cement ratio, and the water-cement ratio of 2:1 has characteristics of high long-term residual strength and small residual strain. When analyzing the strength of the contact surface of the combined body, the D-P criterion is closer to test results than M-C. The strength of combinations is determined by the minimum value of the strength of the contact surface between filling body and other lithology and the strength of the non-standard sample of each lithology. And stress-strain curves of the combined body are elastic-plastic, and all belong to the shear tension composite failure. The UCS of combinations of two lithologies decreases with the increase of the volume ratio of filling body. When volume ratio of filling body is constant, the UCS of the three and four lithologic combinations increases with the increase of volume ratio of sandy mudstone to mudstone. The test results play a theoretical and reference role for the application of original roadway filling without coal pillar excavation in different geological conditions.