Abstract: To investigate the unloading deformation, failure and acoustic emission characteristics during excavation of rectangular roadway under different initial geostresses, excavation unloading model tests were carried out on casted surrounding-rock specimens made of cement mortar. The deformation and failure characteristics of the roof, corner and surrounding rock as well as the evolution characteristics of AE impact count, damage variable and frequency spectrum were obtained. Experimental results showed that: 1) The failure of rectangular roadway was mainly caused by the radial tension strain of the roof and surrounding rock, and the tangential compression strain of the corner. The deformation characteristics of the surrounding rock at the roof were similar to that at the side wall. 2) Increase of the initial geostress had significant effect on the radial strain rate of the roof (or the side wall) and the tangential strain rate of the corner while not significant on others. 3) The evolution characteristics of AE impact count and damage variable revealed the phased failure process of surrounding rock from micro-fracture initiation, expansion to macro-crack development until the occurrence of main fracture. The time of main fracture occurring may be relatively delayed as the geostress increased, and the relative damage proportion after excavation unloading increased nonlinearly with the increase of the initial geostress. 4) The phenomenon that the peak frequency of AE signal was concentrated with gradually increased amplitude could be regarded as a precursor information of the main fracture occurring in the surrounding rock. The higher the initial geostress, the wider the distribution of the peak frequency concentrated section. 5) As the initial geostress increased, the inner wall of surrounding rock specimens demonstrated the evolution of damage from micro-cracks to abscission layer, and to block fracture of rock mass. The failure modes of rock mass were dominated by the tensile heave in the roof and side wall, and accompanied by the phenomenon of delamination and fragmentation. Furthermore, compression and shear failure were observed at the corner when the specimens lost the bearing capacity.

Key words: initial geostress, rectangular roadway, excavation unloading, deformation failure, acoustic emission