Xiaoran Wang

Fracture Mechanical Behavior of Sandstone Subjected to High-Temperature Treatment and Its Acoustic Emission Characteristics Under Uniaxial Compression Conditions

An analysis of the physical–mechanical properties and acoustic emission (AE) characteristics of rock following high-temperature treatment provides theoretical guidance for detecting thermal stability in underground engineering under high-temperature conditions. The physical and mechanical properties of rock, including density, wave velocity, porosity, peak strength, elastic modulus, and deformation modulus, change after subjection to hightemperature treatment (Tian et al. 2012; Ozguven and Ozcelik 2013; Wang et al. 2015). The internal composition and structure of rock materials under such conditions undergo complex physicochemical changes, eventually resulting in cracking by thermal expansion (Chmel and Shcherbakov 2015). Sandstone is a common sedimentary rock, used in a broad array of geotechnical engineering applications and present in many coal mines (Tian et al. 2012; Zhu et al. 2016). AE technology can help deepen our understanding of deformation and fracture of rock materials after high-temperature treatment. Because of differences in mineral composition and structure, previous studies have not reported on differences in AE time domain characteristics and the spatial evolution of sandstones. In this work, we studied the differences in physical–mechanical properties and AE characteristics during deformation and fracture of thermally damaged sandstone. Uniaxial compression tests were carried out, while simultaneously monitoring AE signals. The time & Enyuan Wang weytop@263.net

Study on Ultrasonic Response to Mechanical Structure of Coal under Loading and Unloading Condition

Ultrasonic technology can be applied to study the changes in the internal defects of coal under quantitative loading, which can provide the theoretical basis for applying the technology to determine the structural stability of coal and predict disasters related to the dynamics of coal or rock. In this paper, to investigate the propagation laws of ultrasonic signals through a coal material under various loading conditions, an ultrasonic test system for the deformation and fracture of coal rock was used and a cyclic loading and unloading pattern is adopted. In addition, changes in ultrasonic parameters such as amplitude, dominant frequency, and velocity were analyzed. At the initial loading stage, the ultrasonic amplitude, amplitude of the dominant frequency, and wave velocity slightly decrease as the loading process progresses, and these three ultrasonic parameters gradually increase to their maxima when the stress level reaches approximately 46%. When it progresses from the linear elastic stage to the elastic plastic stage, the material inside the coal distorts and fractures more drastically, the inner defects are fully developed, and the acoustic parameters decrease significantly. Therefore, the corresponding measures should be adapted to reduce the loading stress before the coal is loaded to its critical stress level.

The Time-Space Joint Response Characteristics of AE-UT under Step Loading and Its Application

The acoustic emission (AE) and ultrasonic (UT) simultaneous monitoring program is designed using concrete samples under step loading. The time-varying response characteristics of AE-UT are studied and the cross-correlation analysis between AE-UT parameters is obtained. Moreover, the joint response of UT-AE spatial distribution field is analyzed, and an AE-UT joint monitoring method to detect early-warning signals of a rockburst disaster in a coal seam is proposed. The results show the following. During the loading process, the AE pulses/energy and UT attenuation coefficient first slowly decrease and then increase steadily and finally rapidly increase, while the UT velocity shows a trend of first gradually increasing and then slowly decreasing and finally a sharp decline. AE pulses and energy are significantly or highly correlated with the UT velocity and attenuation coefficient. The AE energy and UT attenuation coefficient can better characterize the damage evolution of concrete under step loading. The UT field evolves ahead of the rupture on the surface, and the long/narrow strip distribution region of UT parameters is consistent with the future failure zone; meanwhile, the AE events can visually reflect the evolution path of internal damage as well as the dynamic migration mechanism of UT field.

Physical Simulation and Monitoring the Deformation and Fracture of Roadway in Coal Mining

Aiming at the large deformation and the dynamic fracture of roadway during the underground excavation or mining, a physical simulation and strain testing system was established, and the deformation process of surrounding body and its inner strain characteristics of the simulated roadway under loading was carried out. Results showed that the inner strain change of the measurement points can be divided into three types: the strain firstly increases and then decreases, the strain slowly increases and then increases sharply, and strain firstly reduces and then increases. The strain starting time is closely related to the failure path and boundary of tested samples. This paper suggested two criteria for determining the instability of roadways, which are a huge and faster increase of strain at the location of the roof and floor with high absolute value, or a small increase with a peak value or irregular fluctuation. This paper provides a new idea for the simulation of roadway instability and is significant in deeper understanding the deformation and destabilization of underground roadway.

Early-Warning of Rockbursts Based on Time Series Analysis of Electromagnetic Radiation Data

Based on time series analysis of electromagnetic radiation (EMR), an EMR model of rockburst early-warning was established to quantitatively analyze EMR trends and characterize EMR precursors before an impending rockburst phenomenon, with the goal to improve the EMR prediction accuracy of a rockburst danger. The model includes two parts: one is warning criterion of EMR abnormity based on normal distribution of mean and variance parameters; the other is the risk identification method based on trends forecast utilizing time series analysis. It has been applied successfully at the No.237 working face in Hegang coalmine. The results show that the model can quantitatively determine the degree of rockburst risk and identify hazardous area, which provides a profound basis for the quantitative identification of electromagnetic radiation precursor and accurate prediction of rockbursts.