Study on capillary water absorption characteristics and time course modeling of water absorption in mudstone

Abstract

[Objective] To study the capillary water absorption characteristics of red mudstone and the change rule of water absorption with time, to put forward the prediction method of water absorption of mudstone, and to carry out the calculation of the critical value of water absorption accordingly, so as to provide references for the prediction of water absorption, theoretical and experimental research on the softening characteristics of water absorption and the analysis of disaster-causing mechanism of red mudstone under the condition of groundwater. [Methods] The red mudstone of the Tertiary Mingshan Formation of Yaan, Sichuan, the Cretaceous Guankou Formation of Jianyang, Sichuan, and the Cretaceous Jishan Formation of Chengxian, Gansu, were taken to carry out the capillary water absorption test, and combined with the X-ray diffraction test, the pressurized mercury test, the contact angle test, and the SEM test, to analyze the micromineral compositions of the red mudstone, the pore structure, the microstructural changes before and after capillary water absorption, the characteristic curves of capillary water absorption law and its influencing factors. [Results] The results show that: the capillary water absorption characteristics of the red bedded mudstone in different regions have some differences, and the capillary water absorption rate is decreasing; the capillary absorption coefficients are positively correlated with the absorption rates; the absorption heights show a good linear relationship with the square root of time; based on the L-W equation and the theory of capillary water absorption in porous media, and considering the influence of mineral composition on the capillary water absorption, a time course model of capillary water absorption is proposed; the capillary water absorption rate is negatively correlated with the content of quartz(R²=0.79) and positively correlated with the content of clay minerals(R²=0.80). [Conclusion] The capillary water absorption characteristics and influencing factors of mudstone have certain regularity, and the capillary water absorption of red bedded mudstone is divided into water adsorption phase and water migration phase at the microscopic level; the proposed time-course model of capillary water absorption can effectively carry out the prediction of the water absorption of red bedded mudstone, and the error is small.

Keywords

red bedded mudstone / capillary water absorption test / capillary water absorption characteristics / water absorption / time-course modeling / influencing factors / scanning electron microscopy testing / microstructure