The rheology of cement grouts often plays a crucial role in the success of rock grouting. In practice, the rheological parameters should be timely adjusted according to the evolution of grouting pressure, flow rate and injection time. However, obtaining the magnitude of rheological parameters is not easy to achieve under site conditions. More importantly, the ground temperature in deep rock masses is elevated higher than that on the surface or under room conditions, which has been demonstrated to strongly influence the rheological properties of grouts. Reasonable understanding and control of the rheological behavior of cement grouts at true ground temperatures is very important to the quality of grouting. This paper aims to propose a simplified method to approximately estimate the initial yield stress and viscosity of cement grouts for rock grouting under elevated ground temperature that actually exists in deep rock masses, on the basis of the flow spread test. The temperature investigated was controlled between 12 °C and 45 °C to simulate the true ground temperature in rock masses with a maximum depth of 1500 m below the surface. Taking the influences of elevated temperatures into account, a temperature-based model for estimating the initial viscosity of cement grout was successfully developed on the basis of Liu’s model and the results of the flow spread test. However, the yield stress failed to be estimated by the Lapasin model due to the absence of plastic behavior of cement grouts. In contrast, yield stress can be linearly correlated to the measured relative flow area. In this work, it was also found that the dependence of yield stress of cement grouts on relative flow area is a strongly exponential law. The temperature dependence of the viscosity of water was accounted for in both estimations of viscosity and yield stress of grouts. Significantly, it was found that the packing density of cement is dependent on the grout temperature, especially when the temperature is up to 45 °C. The proposed method in this work offers an alternative solution for technicians to reasonably control the rheological properties in the increasing applications of deep rock grouting.
In order to study the characteristics of high water-content materials (HWC) undergoing chloride erosion, we analyzed and summarized changes in strength, elastic modulus, and mass of HWC materials during chloride erosion using specific experimental research, and we also described the compression failure morphologies of HWC materials after erosion. e cuboid specimens developed a horizontal crack between the top and bottom, and the cylindrical specimens developed irregular encryption cracks at the top during increasing pressure. e erosion of HWC materials exposed to calcium chloride (CaCl 2 ) solutions was relatively serious, and the erosion of the cuboid specimens was lower than that of the cylindrical specimens. e strength of HWC materials increased during prolonged erosion, and the strength of the cylindrical specimens in water was the highest, followed by the CaCl 2 and sodium chloride (NaCl) solutions. However, the strength change of the cuboid specimens after 28 d was contrary to the above order. In late erosion stages, the HWC materials had better compactness and experienced smaller compressive deformation in water than the other two solutions. In the NaCl solution, the high-water filling material had more pores and a larger deformation than the other solutions.
In order to analyze the stability of the stope under continuous mining with the room–pillar method for a kind of orebody with a long inclination, but not deep mining, this paper takes the room–pillar method for the continuous mining of a long-inclination orebody in the Mengnuo Lead–Zinc Mine, Yunnan Province as the research background. On the basis of the analysis of the stope mechanical model of a long, inclined, thin orebody with room-and-pillar mining, based on numerical simulation, the nature of the change in stress, displacement and the plasticity zone of the roof and pillar during continuous mining along the inclination are systematically analyzed. The results show that as the mining depth increases, the roof subsidence of the stope in the middle of the current operation increases. With the continuous mining of the lower middle section, the roof displacement of the stope will continue to increase with the subsequent mining of the middle section until the end of all stope operations, and the roof displacement of the stope has an obvious cumulative effect. The stress on the roofs and pillars increases with the gradual downward movement of the mining in each level, and the distribution of the plastic zone also expands. It shows that the stope structural parameters that are set according to shallow mining cannot fully meet the requirements of stability and safety in mining a deeper orebody. Therefore, for the mining of a non-deep orebody with a greater tendency to extend, the structural parameters of a shallow stope should not simply be used in the mining of a deeper orebody, but the pillar size should be appropriately increased or the spacing between the room and pillar should be reduced to ensure the stability and safety of the continuous stope.
An advanced break or a vast region of pressurisation may occur when the working face passes through an abandoned roadway, resulting in a roof falling or water inrush. The stress evolution of the working face passing through an abandoned roadway in a coal mine was comprehensively discussed using theoretical analysis, numerical simulation, and field monitoring. In this study, the calculated critical width of the abandoned roadway where the main roof was bound to an advanced break was 5.4 m. Reducing the suspended length of the main roof is beneficial to the stability of the working face’s passage across the abandoned roadway. The maximum abutment stress on the roof occurred at the working face through a semi-abandoned roadway, reaching 44.3 MPa. Subsequently, it decreased sharply until the working face completely passed and returned to the normal level. The damage depths of the floor strata from the field monitoring were 15 and 20 m, which showed that the use of hydraulic fracturing technology combined with floor grouting and hydraulic support for the abandoned roadway was proposed to stabilise the working face for safe mining.
In order to create more underground space, it was important to investigate the impact of excavation on the preexisting building. In this paper, a scale model test was conducted to analyze the stability of the structure during excavation. The model consisted of underpinning piles preinstalled in clay, with a reinforced concrete building placed on underpinning piles. The strain and settlement of the structure were observed to reveal the time settlement of columns and the time strain of beams, columns, and piles during excavation. The results showed that the strain change of beams was small, and strain values of columns were getting higher. And underpinning piles had great strain variations. They were of great significance to underpinning design and engineering practice.
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