The argillaceous slate obviously shows softening characteristics under water-rock interaction. The relationship between the uniaxial compressive strength (UCS)

elastic modulus

Poisson’s ratio and water absorption time in the softening process of argillaceous slate is analyzed by conducting uniaxial compression tests. The laws of pore generation

expansion and breakthrough in the softening process under water-rock interaction are studied by using the nuclear magnetic resonance (NMR). The relationship between porosity and water absorption time in the softening process is analyzed. The evolution rule of microstructure in the softening process of argillaceous slate under water-rock interaction is analyzed by the scanning electron microscope (SEM). Based on the fractal theory

the change rule of the fractal dimension under different soaking time is studied. The fractal dimension value of pore microstructure

porosity

UCS and elastic modulus are selected as the changes of describing the interaction system of argillaceous slate and water solution by using the nonlinear dynamics theory. The applicability of the model is verified with experimental data. The results show that UCS and elastic modulus decrease with the increase of water absorption time

showing a negative linear correlation

but there is no obvious relationship between the Poisson’s ratio and water absorption time. At the early stage of immersion

the water-rock interaction is strong

and the micropores in the slate expand and penetrate to form larger pores

and the porosity increases rapidly. With the increase of water absorption time

the pores in the argillaceous slate are connected with each other to form large pores

which leads to the complex network structure. The fractal dimension of argillaceous slate increases logarithmically and tends to be stable gradually. The results calculated by the nonlinear model are close to the experimental data

which shows that the softening process of argillaceous slate has the obvious nonlinear dynamic characteristics

and the softening law of argillaceous slate under water-rock interaction can be better characterized by the nonlinear dynamic model. The results can provide a reference for the theoretical study of soft rock-water interaction.