*Article* **Study of the Microstructure Characteristics of Three Di** ff**erent Fine-grained Tailings Sand Samples during Penetration**

### **Yueqi Shi \*, Changhong Li and Dayu Long**

Key Laboratory of Ministry of Education for High-E fficient Mining and Safety of Metal Mines, University of Science and Technology Beijing (USTB), Beijing 100083, China; lch@ustb.edu.cn (C.L.); ldayu2018@163.com (D.L.) **\*** Correspondence: syq\_shi@126.com

Received: 3 March 2020; Accepted: 27 March 2020; Published: 30 March 2020

**Abstract:** This paper explores the microstructural evolution characteristics of tailings sand samples of di fferent types of infiltration failure during the infiltration failure process. The homemade small infiltration deformation instrument is used to test the infiltration failure characteristics of the tailings sand during the infiltration failure process. Evolutionary characteristics of the internal microstructure pores and particle distribution were also studied. Using CT (computerized tomography) technology to establish digital image information, the distribution of the microscopic characteristics of the particle distribution and pore structure after tailing sand infiltration were studied. Microscopic analysis was also performed to analyze the microscopic process of infiltration and destruction, as well as to see the microscopic structural characteristics of the infiltration and destruction of the total tailings. The test results show that there are obvious di fferences in the microstructure characterization of fluid soil and piping-type infiltration failures. Microstructure parameters have a certain functional relationship with macrofactors. Combining the relationship between macrophysical and mechanical parameters and microstructural parameters, new ideas for future research and the prevention of tailings sand infiltration and failure mechanisms is provided.

**Keywords:** X-ray microtomography; microstructure characteristics; infiltration damage
