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.