Pore Changes in Purple Mudstone Based on the Analysis of Dry-Wet Cycles Using Nuclear Magnetic Resonance

Chen Dang,Zhili Sui,Xiuyuan Yang,Zhenlong Ge,Zengshun Chen

doi:10.1155/2022/5578401

Abstract

The study on the change of rock pore structure during the weathering of purple mudstone is of guiding significance to the stability of the bank slope of the three gorges reservoir. In this paper, the pore changes in the wet and dry circulation of purple mudstone in the three gorges reservoir area are studied by means of nuclear magnetic resonance (NMR). The results show that the simulated weathering of wet and dry circulation has a great influence on the purple mudstone. With an increase in the number of dry-wet cycles, the purple mudstone pore volume ratio significantly changed. Originally, it consisted of a small pore structure with a single pore diameter of 0.01–0.1 µm and changed to a variety of pore structures with various pore diameters of 0.001–100 µm. With the increase in the number of dry-wet cycles, the micropores (0.001–0.1 µm) were transformed into macropores (0.1–1 µm). The area of the second peak of the three samples (large pores 0.1–1 µm) increased from 0.9413, 0.9974, and 0.6779 to 0.9871, 1.1498, and 0.9901, respectively.

Highlights

Owing to the requirements of engineering construction projects, including tunnels, mining, and rock excavations, current research on the effects of water-rock chemistry on the physical and mechanical properties of rock masses has become a hotspot for geotechnical engineering [1]. e drywet cycle has a great influence on rock properties and the geological environment
A Niu Man MacroMR low-field nuclear magnetic resonance (NMR) instrument was used to test the porosity changes of the purple mudstones under multiple dry and wet cycle periods. e sample was placed in a blast drying box to dry, and the sample was placed in a vacuum saturation tank to be saturated. is constituted the drying and wetting cycles. e saturated sample was removed from the tank, the surface water wiped off, and the sample was sealed with two layers of plastic wrap to prevent moisture from dissipating and any external interference
Many factors affect the pore structure during dry-wet cycles, including water, accumulation of salt crystals, and crystal expansion. ese are discussed in detail

Summary

Introduction

Owing to the requirements of engineering construction projects, including tunnels, mining, and rock excavations, current research on the effects of water-rock chemistry on the physical and mechanical properties of rock masses has become a hotspot for geotechnical engineering [1]. e drywet cycle has a great influence on rock properties and the geological environment. Water storage and drainage of the ree Gorges Dam on the Yangtze River, groundwater seepage, and seasonal precipitation cause changes in reservoir water levels, and the rock mass is periodically in a drywet state. Changes in physical properties have been used to evaluate rock deterioration and damage after dry-wet cycles. Using Yangtze River water and distilled water to study the effects of the dry-wet cycles, these authors compared the rock deterioration in these two cases and concluded that the degradation effect of distilled water on sandstone was lower than that of river water, providing a more accurate method for evaluating geological disasters and engineering faults [2]. Testing the dry-wet cycle under acidic conditions, the corrosion of underground engineering by acid rain has been simulated, and the changes in the microscopic pore structure of sandstone under the combined effect of an acidic environment and dry-wet cycle were examined to provide a reference for the safety and

Methods

Results

Conclusion