Study on the Law of Failure Acoustic–Thermal Signal of Weakly Cemented Fractured Rock with Different Dip Angles

Step by step and combined supporting technique with allowable deformation + limiting shape for soft rock roadway

Aiming at the difficult problems of the large deformation in weakly cemented soft rock roadways, the reasons of large deformation are analyzed for roadways in Hongqingliang coal mine. On this basis, the principle of step by step combined support technology based on allowable deformation + limiting shape for weakly cemented soft rock roadway is proposed, and the optimal support parameters of step by step combined technology are determined by FLAC3D. Step by step combined support technology includes the primary support of anchor bolt + anchor cable + initial shotcrete and the secondary support of U-shaped steel shed + filling flexible material behind shed + control of key parts. The comparative analysis on the site shows that the deformation rate and final deformation amount of the surrounding rock after the step by step combined support are less than those of the primary support, and the deformation of the surrounding rock can be controlled effectively after the secondary support is added. Step by step combined support is superior to the traditional bolt + anchor cable combined repair in terms of economy and efficiency. The optimal construction period of each working procedure of the step by step combined technology is 28 days after the completion of the first support, and the step by step combined support based on allowable deformation + limiting shape is an effective way to control the surrounding rock of soft rock roadway.

Study on the evolutionary characteristics of strain energy on crack propagation in coal and rock under bending load

The failure of coal mine overburden is mainly caused by fractures under bending loads. The energy evolution characteristics of coal and rock fractures are closely related to coal mine disasters such as rock burst. To obtain the characteristics of energy release and accumulation of coal and rock under bending load, three‐point bending tests of coal, mudstone, and sandstone were carried out respectively. The strength characteristics and fracture propagation process of coal and rock under bending load were studied. The strain energy evolution rules of coal and rock were calculated and obtained. The fracture mechanism of coal and rock was discussed by analyzing the critical strain energy release rate. The results show that the fracture complexity of sandstone and mudstone is greater than that of coal. The microstructure and its directivity in coal and rock indirectly affect their fracture characteristics through the elastic modulus characteristics. The distribution of parameters such as peak load of fracture, fracture energy, and crack length of coal and mudstone samples is discrete, while that of sandstone samples is concentrated. The deformation energy density of coal and rock basically shows a linear increase trend at the prepeak stage. The deformation energy density evolution characteristics at the postpeak stage are mainly affected by the load drop. It is important to establish the internal relationship between the meso structural characteristics and macro mechanical properties for solving engineering problems.

Influence of Stress Disturbance on the Deformation of Nearby Cemented Roadways following the Excavation of Chambers

Based on the engineering background of weakly cemented roadways and adjacent chambers in Western China, a numerical simulation method was used to examine the changes in stress distribution and increment in the surrounding rock of weakly cemented roadways adjacent to chambers. The results show that the surrounding rock stress of the weakly cemented roadway adjacent to the chambers increases by approximately 30%. The vertical stress of the surrounding rock mainly expands along the vertical direction, and the expansion range is 7–12 times that of the chamber height. The horizontal stress of the surrounding rock mainly expands along the horizontal direction, and the expansion range is 3–6 times that of the chamber width. Based on the support idea of “allowable deformation” + “relief pressure” + “maintaining roadway shape”, the support technology of weakly cemented roadways adjacent to chambers is established with “full section U-shaped steel shed + filling flexible materials between the steel shed and surrounding rock + patching the roof bolt + laying concrete on floor”. An engineering test based on the above support technology was carried out, and it was found that the deformation of the weakly cemented roadway adjacent to the chambers was 0 in 20 days.

Stability analysis and deformation control method of swelling soft rock roadway adjacent to chambers

The surrounding rock of swelling soft rock roadway has high clay mineral content, strong expansibility after encountering water, low strength and poor cementation. The roadway is prone to large deformation under the influence of complex geostress. Combined with the support change of the development roadway of 2# coal in Hongqingliang mine, through geological survey, field observation and indoor test, the failure mechanism of the traditional support method of “anchor bolt + anchor cable + anchor mesh + shotcrete” was revealed by the adjustment of the surrounding rock stress after the excavation and support of the adjacent chambers. The research results show that the surrounding rock stress will cross the adjacent chambers and form a concentrated area near the weakly cemented roadway, and the maximum stress increase ratio of surrounding rock within the stress concentration range will reach 50%. The farther the chambers are from the weakly cemented roadway, the smaller the range of the surrounding rock stress concentration area. When the distance exceeds about 12 times the average height of the chambers, the surrounding rock stress concentration tends to disappear. Based on the fully enclosed combined support method of the "U-shaped steel sheds closure roof and sides + filling flexible material behind the sheds + laying reinforcement mesh and concrete in floor + strengthening key parts", the construction process flow applicable to the working condition of swelling soft rock roadway is formulated.

Study on Stress Disturbed Mechanism and Supporting Method of Weakly Cemented Roadway near Chambers

After excavation of the weakly cemented roadway adjacent to the chambers, deformation characteristics such as roof subsidence, roadway extrusion, and floor heave appear, showing the characteristics of large deformation of surrounding rock, long deformation duration, and serious damage, which are not conducive to guaranteeing safety mining. Based on the technical means of the rock mechanical property test, mineral composition analysis, in situ stress test, and surrounding rock deformation monitoring of 2# coal roadway in Hongqingliang coal mine, a numerical simulation study on the influence of surrounding rock stress on adjacent chamber groups was carried out. The physical and mechanical properties of the weakly cemented rock were obtained, the stress distribution law of the 2# coal roadway was mastered, the deformation characteristics of the surrounding rock of the weakly cemented roadway were obtained, and the deformation and failure mechanism of the weakly cemented roadway adjacent to the chambers were revealed. The relationship between the regional stress increment of the chambers and the failure range of the surrounding rock of the roadway is revealed, establishing a mechanical model of allowable deformation + stress release + controlled form with U-shaped steel as the main structure. The roadway support countermeasures were given and applied in engineering practice.