With the increase in mining depth, the problem of the floor heave of a roadway is becoming increasingly prominent. Solving this problem for a deep high-stress roadway is the key to ensure safe supply and utilization of coal resources in China. This study investigates the floor heave of a horizontal transportation rock roadway at the depth of 960 m at the Xieyi Mine. A four-way loading simulation test frame similar to the Xieyi Mine was used to reproduce the high-stress environment of a deep roadway by loading different pressures on the roof, floor, and two sides of the roadway. The experimental results show that after the tunnel had been excavated, the surrounding rock failure could be divided into three stages: the initial deformation stage, fissure development stage, and mild deformation stage. The destruction time periods of these stages were 0–0.5 h, 0.5–2 h, and 2–6 h, and the destruction ranges were 0.4 m, 1 m, and 1.5 m, respectively. The amount of roof subsidence, the displacement of the two sides, and the floor heave influence each other, and the range of the bearing ring (5.6 m) of the floor is larger than that of the roof (3.4 m) after the surrounding rock has been damaged. The findings suggest that the floor should be supported first, before the two sides and the roof; then, the support of the key parts (roof and floor corners) should be strengthened. The roof, floor, and two sides are considered for controlling the deformation of the surrounding rock in a coupled trinity support mode. Because of the unfavorable conditions in the area, overexcavation backfill technology was used. The new support was successfully applied during the subsequent construction of the rock tunnel. Based on the long-term monitoring results of the surrounding rock deformation, the floor heave control yielded satisfactory results and maintained the long-term stability of the roadway. Therefore, this study can serve as a reference for preventing floor heave in similar high-stress roadways in the future.
In recent years, the structural evolution characteristics of the regenerated roof of the lower coal seam have become a research hotspot when the bifurcation coal seam is mined downward. In this paper, taking the bifurcation coal seam of Xutuan Coal Mine in China as an example, the structural evolution characteristics of regenerated roof under the influence of mining in bifurcation coal seam are comprehensively studied by theoretical analysis, field measurement, and indoor similar simulation experiment. The stress transfer law in the floor after mining in the upper coal seam is also analyzed. The results show the overburden structure and stress field change caused by upper coal seam mining. The caving and fracture zones are formed in the roof, the average height of the caving zone is 8.28 m, and the one of the fracture zone is 34.91 m. The results of the field test verify the accuracy of theoretical analysis and similar simulation test results. According to the relative size of the depth of the strong failure zone of the coal seam floor and the coal seam spacing, the rock mass structure of the regenerated roof of lower coal seam is divided into three types: fractured rock mass + scattered rock mass (I), fractured rock mass + scattered rock mass + fractured rock mass (II), and fractured rock mass + bulk rock mass + fractured rock mass + layered rock mass (III), and the stability of the three types of regenerated roof structure is evaluated: III > II > I. The research in this paper can provide a theoretical basis for determining the target area of broken roof control under the mining conditions of bifurcation coal seam and provide guidance for the selection of the location and parameters of the grouting borehole for roof reinforcement.
During downward mining of a bifurcated coal seam, the roof of the lower coal seam is relatively broken and difficult to control due to the mining influence of the upper coal seam. Roof accidents occur frequently during mining of the lower coal seam, reducing mining efficiency. How to ensure safe and efficient mining of the lower coal seam is a significant issue. In this paper, overlying strata migration and fracture characteristics of the lower coal seam, the structure and stability of the regenerated roof, and porosity and permeability characteristics of the overlying strata under the mining influence of the upper coal seam are studied by using similar simulation tests. Results show that the overburden structure of the lower coal seam is altered due to the mining influence of the upper coal seam, and the regenerated roof of the lower coal seam is divided into three structural types from top to bottom, namely: intact rock mass+block fracture rock mass+loose rock mass (type I structure); intact rock mass+block fracture rock mass+loose rock mass+cataclastic rock mass (type II structure); and intact rock mass+block fracture rock mass+loose rock mass+cataclastic rock mass+slab-rent rock mass (type III structure). The stability of each type of rock mass structure is evaluated, and the stability of three types of rock mass structures is III > II > I. The overburden porosity and slurry permeability coefficient are relatively large at the cutting hole and stopping line. The porosity of the caving zone within 70 m of the cut hole and stopping line is greater than 5%, and the permeability coefficient is greater than 0.1 m/s. Based on differences in the surrounding rock porosity and permeability characteristics, the grouting difficulty of overburden is divided into three types of areas: extremely easy grouting areas, easy grouting areas, and difficult grouting areas. The results of this paper can provide reference for the stability evaluation of the regenerated roof and the selection of grouting treatment parameters for the broken roof under similar conditions.
Soft broken surrounding rock exhibits obvious rheological properties and time-dependent weakening effects under the action of deep high-ground stress, leading to the increasingly prominent problem of sustained large deformation in deep roadways. In this study, with the II5 Rail Rise in Zhuxianzhuang Coal Mine as an example, the mechanism and control technology of time-dependent damage and instability in a deep soft-rock roadway were explored through a field observation and numerical simulation. The research results show that the range of the loose circle in the deep fractured surrounding rock can reach 3.0 m. The expansion of shallow and deep cracks causes the primary plastic deformation and secondary rheological deformation of the surrounding rock, with the rheological deformation rate increasing by 21.4% every 55 days on average, which ultimately induces the instability and failure of the surrounding rock. Based on the mechanism of roadway instability, a control technology of high-preload bolt + deep- and shallow-borehole crack filling was proposed. The technology reduces deformation and ensures the stability of the roadway surrounding rock by inhibiting the propagation of deep and shallow cracks and reinforcing the surrounding rock.
The stability control of surrounding rock in deep roadway is becoming more and more difficult, and grouting reinforcement support has become the mainstream of roadway control. In order to obtain the ratio of quasi-sandstone material corresponding to the grouting body, this paper uses river sand as aggregate, cement and gypsum as cementing agent, retarder and defoamer as additives, and carries out orthogonal proportioning tests with three influencing factors: water-binder ratio (ratio of water to mass of cementing agent), gypsum-cement ratio (ratio of gypsum to mass of cement) and binder-aggregate ratio (ratio of cementing agent to aggregate mass), and compares and analyzes the sensitivity of each factor on the density, compressive strength, tensile strength, elastic modulus, Poisson’s ratio, longitudinal wave velocity, elasticity index and brittleness index of quasi-sandstone material. The results show that 1) the Water-binder ratio has the greatest effect on the sensitivity of material compressive strength, tensile strength, elastic modulus, Poisson’s ratio and longitudinal wave velocity; the gypsum-cement ratio has the greatest effect on the sensitivity of material deformation index and brittleness index; the binder-aggregate ratio has the greatest effect on the sensitivity of material density. 2) Reducing the Water-binder ratio can improve the density, compressive strength and tensile strength of the material; reducing the paste ratio can improve the modulus of elasticity, Poisson’s ratio and longitudinal wave speed of the material; as the gypsum-cement ratio increases, the deformation index first decreases and then increases and then decreases; as the binder-aggregate ratio increases, the brittleness index first increases and then decreases and then increases. 3) The empirical equations between physical and mechanical properties of sandstone-like materials and Water-binder ratio, gypsum-cement ratio and binder-aggregate ratio were established based on multiple linear regression analysis, and more reasonable material ratios were quickly obtained by physical and mechanical parameters of materials. The results of the study provide theoretical references for similar material simulation tests for quasi-sandstone grouting.
To improve the service life of axial piston motor with dual-driving, the cylinder model of axial piston motor with dual-driving is established, the cylinder force is derived and used as the boundary condition, based on the results of finite element analysis, the S-N curve of the cylinder material is modified and fatigue solution is carried out. The results show that: the main stress and strain of the cylinder block are mainly located at the cylinder block hole and the flow distribution window, the stress concentration is generated at the structural mutation, and the stress and strain are the largest; the cylinder block will be repeatedly subjected to high-pressure oil action will produce fatigue damage, fatigue damage mainly occurs at the location of higher stress.
THE EXPERIMENTAL INSTRUMENTED BOLT WITH FIBRE BRAGG GRATING FORCE SENSORSMonitoring the stress change of bolt and knowing the anchoring condition in a reasonable and effective way, accurately, can effectively prevent tunnel accident from breaking out. The stress of rock mass around the roadway is usually transferred to the anchor rod in the form of axial load, so it is of great significance to study the axial load of the bolt. In this paper, a full size anchoring and drawing experiment system was designed and established, innovatively, which realized the pull-out test of 2.5 m prestressed end Anchorage and the full-length Anchorage by using the new resin anchorage agent under vertical and horizontal loads. Through the application of fiber Bragg grating (FBG) sensing technology to the test of full-scale anchor rod, the axial force distribution characteristics of the end Anchorage and the full-length Anchorage anchor rod were obtained under the action of pre-tightening torque and confining rock pressure. The comparison indicates that the proportion of high stress range accounts for only 17.5% and the main bearing range is near the thread end of anchor rod, the proportion of main bearing range of end Anchorage is 83.3%, and the feasibility of FBG force-measuring anchor rod is verified in the field. The research results have certain reference value.
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