Experimental study on loading combination of filling body and surrounding rock.

To investigate the deterioration characteristics of filling body combinations and surrounding rock in excavating technology without coal pillars in the original roadway filling, uniaxial loading destructive tests and cyclic loading and unloading tests were conducted with various combinations of two, three, and four lithologies to analyze strength characteristics, energy storage, and dissipation laws. The results indicate that when the filling is combined with another lithology, strengthening degree of the filling is negatively correlated with the height of other lithology; the higher the strength of the material combined with the filling, the greater the amplitude of the weakening. The filling exhibits a faster speed and higher upper limit of elastic energy storage compared to mudstone. When filling is combined with two or three lithologies, the strength weakening degree is negatively correlated with their height ratio. However, under same cycles, elastic energy of coal-free combinations has a faster storage speed and a higher upper limit, while coal-containing combinations exhibit higher energy dissipation. During tests, the elastic energy of different lithological combinations is linearly related to the number of cycles, and the energy is divided into four stages. The damage variable is exponentially related to the height of the roof and floor. The intrinsic model was modified using the stress-strain relationship considering the internal damage factor in front of the peak and verified to accurately simulate the deformation damage of the combined body.