Abstract: In karst water-enriched tunnel, due to the complexity of water-rock coupling effect, the evolution of pore structure in rock mass is unstable and will induce the deterioration and instability of rock mass, which puts forward higher requirements for the research of the stability of underground permeability rock mass. Firstly, to investigate the effect of osmotic pressure on the karst pore structure, osmotic test, acoustic emission test, mercury injection test, SEM test and fluorescence photometric test were carried out on limestone from Maixi tunnel, Guiyang, treated with different osmotic pressures. Then, the mass loss rates, P-wave patterns and frequency spectrum, pore distribution curves and scanning electron microscope images were obtained. Results show that the mass loss rates of limestone show the tendency of "slow increase-rapid development" with the increase of osmotic pressure, and the demarcation points of the two phases is 6 MPa. With the increase of osmotic pressure, the amplitude of head wave gradually decays, and the waveform curve first decays quickly and then tends to be stable early, and the development degree of wave tail gradually slows down. Also, it is found the peak of dominant frequency gradually decays and evolves from single peak to multiple peak and has excellent quadratic function with osmotic pressure, and that the wave frequency develops from (relatively) high frequency to low frequency. Besides, the macropores and mesopores formed by dissolution play a decisive role in the permeability of limestone. With the increase of osmotic pressure, the accumulation of mercury increases exponentially. Meanwhile, the mineral contents including CaCO3 and SiO2 change exponentially. Compared with chemical dissolution, mechanical dissolution is more sensitive to time and dominates the formation of pores. In additional, the established water-rock contacting dissolution model indicates that the drag force of osmotic water depends on its flow velocity, while the increase of osmotic pressure can enlarge the osmotic pressure gradient, thus increasing the flow velocity.

Key words: limestone, osmotic pressure, water-rock interaction, pore, dissolution action