A physical model experiment was conducted to study the surrounding rock failure mechanism for the roadway under deviatoric pressure from mining disturbance. During the excavation process, a self-developed deviatoric pressure reaction system was used to realize deviatoric pressure loading. Meanwhile, a digital photogrammetric measurement system and a static strain data collection system were utilized to obtain the deformation, strain and stress of the model. The deviatoric pressure stress field characteristic and deformation failure mechanism of roadway were investigated by synthetic analysis of experimental data and displacement vector diagram. The physical experimental results showed that mining disturbance had an inevitable influence on the formation of roadway deviatoric pressure, which caused the V-shaped distribution of pressure stress above the roadway. The V-shaped deviatoric pressure stress caused the roadway asymmetric deformation that was proportional to the deviatoric pressure stress above the roadway. And the asymmetric deformation further aggravated the degree of deviatoric pressure stress and formed a vicious cycle, which resulted in the instability of the roadway. In addition, a numerical simulation under deviatoric pressure was conducted to verify the accuracy of physical experimental results. This study can provide helpful references for researching the instability behavior of the roadway.

An experimental investigation was conducted in order to understand properties of grouts and grouted specimens. Three different cement types, i.e., composite ultrafine cement (CUC) that was independently developed, ultrafine cement (UC), and Portland cement (PC) were injected into broken red sandstone specimens on the basis of a self-designed grouting test equipment. After the grouting test, the effects on the mechanical behavior of grouted specimens were studied using an uniaxial compression test, macroscopic failure analysis and mesostructure analysis, as well as a comparison of the mechanical and structural properties of three types of grouted specimens was presented. The test results show that the compressive strength of grouted specimens improved in comparison to the rock residual strength, and the compressive strength of PC, UC and CUC grouted specimens increased by 23.0%, 59.6% and 101.5%, respectively. The failure modes of all grouted specimens were brittle failure, but only the CUC grouted specimen was failed along the new failure surfaces, indicating that CUC grouts can better bond the original cracks. The mesostructure characteristics obtained through the Digital 3D Video Microscope reveal the superior filling effect of the CUC grouts as well as verifying the macroscopic mechanical behavior.

To investigate the distortion and damage properties of coal-rock combination (CRC) samples, the individual coal samples and rock samples and CRC were developed by similar materials with equal strength. Then, uniaxial compression (UC) tests and acoustic emission (AE) tests were performed on CRC samples with various rock-coal height ratios and loading rates. The strength, deformation, and AE properties of the CRC samples were analyzed to explore their failure mechanisms. The findings indicated that the individual coal samples and rock samples were mainly damaged by tensile splitting. For CRC samples, shear and tensile coupled failures were the main failure modes. Cracks are first generated from coal part and continue to expand to rock part. The coal-rock height ratio had little impact on the single AE event count peak value but had a certain influence on the cumulative number of AE event count. However, the loading rate had a large effect on the AE characteristics, and the strength and elastic modulus (E) of the CRC samples had linear or nonlinear increasing trend with increasing ratio of rock to coal height and loading rate. The research findings will have certain theoretical reference value for analyzing the mechanism of coal pillar failure.

The Hoek-Brown (H-B) failure criterion is an empirical failure criterion. The estimates of Hoek-Brown criterion parameters, such as the geological strength index (GSI) and the disturbance coefficient (D), are usually subjective. This paper focused on modifying the initial estimates of GSI and D to improve the accuracy of parameters. The nonlinear regression model (NLRM) of the Hoek-Brown failure criterion was proposed to analyze the rock parameters by using the sensitivity analysis and the displacement equation of the surrounding rocks. Then, a reasonable back analysis method was developed by introducing the differential evolution (DE), which was used to accurately obtain the parameters of the Hoek-Brown failure criterion in practical engineering. This method was successfully used to analyze the stability of the roadway in a deep coal mine. The results showed that the NLRM can better reflect the relationship between GSI, D, μ and the displacement of roadways, and the back analysis results are consistent with the filed monitoring results. This method can provide a helpful reference for modifying the influence of empirical and subjective factors on H-B parameters selection, and improving the accuracy of Hoek-Brown criterion parameters in the similar engineering applications.