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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.

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.

As a high-efficiency and low-consumption mining mode, multi-middle section combined backfilling mining (MMSCBM) is becoming more and more widely used in metal mines. The geological mining conditions of Baixiangshan Iron Mine were taken as the simulation prototype. Similar model tests and numerical simulation experiments were used to study the surrounding rock disturbance, stope stability, surrounding rock stress, overburden settlement, and dynamic deformation of the ground surface during the MMSCBM process. The evolution process of the stope instability: the stable stage of the pillar, the large deformation stage of the pillar, the failure of some pillars, and the overall failure of the pillar. MMSCBM effectively buffered the excavation’s disturbance to the surrounding rock, adjusted the stress release mode, and changed the stress concentration area. The dynamic deformation laws of the overburden and the surface were summarized. The method of field monitoring was verified by numerical simulation calculation to study the disturbance degree of MMSCBM to the roadway and evaluate the safety of the roadway. This research has important significance and value for the wider application of the mining model.

The Sanshandao Gold Mine is located on a seabed, and the crown pillar is the main barrier to isolating seawater and preventing it from entering the mine. The thickness of the crown pillar and the size of the point pillars have a substantial impact on the reduction of resource waste and the economic development of the mine. Therefore, it is very important to determine a reasonable crown pillar thickness and point pillar size. In this paper, theoretical analysis and numerical simulation were performed to determine a reasonable thickness of the crown pillar and the size of the point pillar in the Sanshandao Gold Mine. According to the law of conservation of energy, a theoretical mechanical model was established based on the “crown pillar-point pillar” support system, and the thickness of the crown pillar, which corresponds to different section sizes of the point pillars, was obtained. Numerical simulation was carried out by combining Geologic Object Computer-Aided Design (GOCAD) and Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D). According to the failure criterion of the elastic strain energy density, the limit value of the elastic energy strain density coefficient of the ore body element and crown pillar was analyzed, the thickness of the crown pillar was determined, and the theoretical derivation result was verified. The point pillar with a section size of 4 m × 4 m was selected, and the crown pillar thickness was 50 m.

Ingestion of jujube pits is a common clinical problem, which can be difficult to diagnose and life-threatening if accompanied with intestinal perforation and peritonitis. In this study, 18 cases of intestinal perforation caused by ingestion of jujube pits were reviewed and summarized to discuss the clinical characteristics, diagnosis and treatments. From 2012 to 2018, a total of 18 patients diagnosed as intestinal perforation due to ingested pits of jujube in our center were retrospectively reviewed and the manifestations, laboratory tests, imaging examinations and treatment strategies were summarized. The patients comprised of 11 males and 7 females with an average age of 63.5 years. The main clinical manifestation was abdominal pain. Twelve patients (67%) presented to the emergency department with signs of localized peritonitis. CT imaging revealed positive findings in 17 (94%) patients. Conservative treatments were attempted in 3 patients, and the other 15 patients received emergency surgical exploration, where 7 patients had more than one perforation identified during surgery. Five patients were admitted in the surgical intensive care unit after surgery. The average length of stay of all 18 patients was 9.8 days (range 5–24 days). Ingestion of jujube pits is a common clinical problem and potentially leads to intestinal perforation and peritonitis. CT imaging is the first imaging modality of choice. Patients with milder symptoms might be managed with cautious conservative treatment, and patients with more than one perforation can be identified during surgery.

A series of triaxial compression experiments of intact and cracked sandstone with different degrees of damage were carried out using a rock mechanics servo-controlled system. Based on the experimental results, the influence of the confining pressure and damage on the peak strength, residual strength parameters, deformation parameters, and failure modes of cracked sandstone was investigated in detail. The results show that the strength and deformation behavior depends on not only the confining pressure but also the damage. The peak and residual strength of intact and cracked specimens increases linearly with increasing confining pressure, which is in good agreement with the linear Mohr-Coulomb criterion. The peak strength and equivalent cohesion of cracked specimens decreases linearly and exponentially with increasing damage, respectively. However, the internal friction angle is independent of damage. The elastic and secant modulus of cracked specimens increases linearly with increasing confining pressure but decreases with increasing damage. Then the effects of the confining pressure and damage on the peak strain and failure modes of cracked specimens are also analyzed in detail, indicating the transition of the failure modes from single shear failure to multiple shear failure with increasing damage.