China’s coal mines are mainly underground mines, and a large number of roadways have to be excavated underground. It is of great significance for coal mine production to adopt safe and reasonable roadway support methods. In the process of roadway excavation, the rock stratum is inclined and the roadway pass through the layer. Since the surrounding rock conditions of the roadway passing through the layer are more complicated, it is easy to cause deformation of surrounding rock, failure and floor heave, which makes the support work difficult. In order to solve this problem, the mechanical properties of roadway surrounding rock were tested and the failure of roadway surrounding rock was analyzed using the +260 horizontal centralized transportation roadway in Changcheng No.2 mine. The surrounding rock of the roadway was divided into 8 regions, and the stress analysis of the surrounding rock in different regions was carried out. It is found that the left shoulder pit, the right side and the floor of the roadway are prone to damage. The influence of the lateral pressure coefficient, the rock dip angle and the lithology on the failure of the roadway surrounding rock was analyzed by Mohr-Coulomb failure criterion, and the specific failure range of the roadway surrounding rock was obtained. The support optimization design of the roadway was carried out, and the weak area of the surrounding rock was reinforced. The deformation monitoring of roadway surrounding rock after support optimization was carried out. The field monitoring results show that after the optimized support, the displacement of the roof and floor of the roadway section and the two sides are reduced by 43.6% and 40.8% respectively compared with the original scheme, and the deformation of the surrounding rock also shows a trend of gradual stability, and the surrounding rock of the roadway is effectively controlled. The research can provide a new way for the stress and failure analysis of the surrounding rock of the inclined rock roadway.

Study on failure mechanism and control of surrounding rock of inclined strata crossing roadway in deep coal mine

This paper presents a novel design for uplift piles incorporating a composite-anchor system. The composite-anchor system consists of steel strands, a non-expansion grouting body, and a high-strength steel pile. The aim of this design is to enhance the mechanical performance, durability, and economic efficiency of uplift piles. To evaluate the performance of the new pile, three sets of full-scale load tests were conducted, focusing on their in situ capacity, deformation, and stress characteristics. Despite a significantly lower reinforcement ratio of 0.75% compared to conventional piles with a ratio of 3.84%, the new uplift piles exhibit an exceptional uplift bearing performance. The utilization of the lateral friction resistance of the lower pile body is significantly improved, leading to enhanced load distribution and stress transfer mechanisms. Furthermore, a numerical model was developed and validated against the experimental results, demonstrating its reliability in simulating the bearing characteristics of the new uplift piles. The multi-interface design of the composite-anchor system ensures the efficient transmission of internal forces induced by external uplift loads, resulting in an improved stress state within the pile body. Moreover, the multi-layer structure of the composite main bar enhances the durability of the uplift piles. In comparison to conventional piles, the new uplift pile design offers substantial advantages, including an 80% reduction in reinforcement ratio, a 65% reduction in reinforcement cage welding, a cost reduction of approximately 30%, and a shortened construction time by around 20%. These findings highlight the potential of the new composite-anchor-pile design to revolutionize the field of uplift pile applications, offering improved efficiency and effectiveness. 

Development and Mechanical Property Analysis of a Novel Uplift Pile Incorporating Composite Anchors

The development and expansion of underground space has led to a continuous increase in both the occupied area and the burial depth of underground basements. Meanwhile, due to the inaccurate estimation of groundwater buoyancy, more and more anti-floating problems of underground basement caused by rainstorm have emerged. Combined with the principles of unsaturated seepage theory, this article uses Flac3d 6.0 software to conduct simulations on the influence of various significant factors on the effect of the water discharge pressure relief method, a novel approach to reduce buoyancy. The numerical results show that the water discharge pressure relief method can ensure the stability of the basement under rainstorm conditions compared with the basement without drainage holes. In order to improve the anti-floating efficiency of the water discharge pressure relief method in preventing floating, it is recommended to initially decrease the height and spacing of the drainage holes and follow by increasing the aperture of the drainage holes. The recommended spacing of the drainage holes is between 2 m and 3 m. The height of the drainage holes should be between 1 m and 1.5 m, and the aperture of the drainage holes should be no smaller than 100 mm. Furthermore, the water head of the basement floor is proportional to the permeability of the lower backfill and cushion, and it is not significantly influenced by the upper backfill soil when its permeability is within a low range. Finally, in order to achieve a satisfactory anti-floating effect, it can be attempted to reduce the longitudinal width of the lower backfill soil or moderately increase the thickness of the cushion. 

Numerical Simulation Study of Basement Water Discharge Pressure Relief Method under Rainstorm Conditions

During the construction of a highway in northwest China, large deformation of mudstone caused severe deformation of and damage to side walls, initial support, and secondary lining to various extents. To reveal the causes of mudstone’s large deformation in the tunnels of this highway, a comprehensive study was conducted by using engineering geological survey, on-site monitoring and measurement, indoor rock mechanics test, numerical simulation, and macroscopic analysis. For the problem of large deformation of this highway’s tunnel section from YK209 + 500 m to YK210 + 030 m, the 3D finite difference method FLAC3D was used to simulate the large deformation of the wall rock and compare the deformation of the tunnel and the mechanical characteristics of the lining structure under different conditions by means of inverse analysis of the rheological characteristics of the mudstone and simulation of the softening of the mudstone in water. The research results provide a reference and basis for the construction design of similar mudstone tunnel projects. For the management of tunnel deformation, it is recommended to enhance the tunnel’s drainage measures, thereby mitigating the intensification of mudstone softening when exposed to water.

Research on intrusion and large arch bulge in lining structure for highway’s mudstone tunnel

This paper introduces a new type of uplift pile known as the composite-anchor pile, which employs a composite anchor composed of steel strands, grouting materials, and steel pipes as the main reinforcement. This paper extensively analyzes this pile’s load-bearing capacity and deformation characteristics through full-scale field tests and three-dimensional finite element numerical simulations. The results show that the composite-anchor pile has a more even distribution of stress, and its endurance and mechanics performance are better than others. Furthermore, this study utilizes a three-dimensional finite element refined model that has been validated using on-site test results to examine the influence of key parameters, such as the pile diameter, the number of composite-anchor cables, and the diameter of steel strands, on the load-bearing capacity of uplift piles. Building upon these findings, this paper introduces a calculating method to determine the bearing capacity of composite-anchor piles, thereby addressing the existing gap in this field. 

Finite Element Analysis of Load-Bearing Characteristics and Design Method for New Composite-Anchor Uplift Piles

Buildings (structures) with various structural forms are becoming increasingly prevalent and are encountering more challenging engineering issues. Field investigations, laboratory tests, and numerical simulations were used to study the disaster-causing mechanism and the control technology for a variable cross-section tunnel passing through layered, expansive mudstone stratum. The deformation and stress characteristics of the surrounding rock and supporting structure were examined by both numerical simulation and field monitoring. The results indicated that the stress was more complex at different section positions; the rock and supporting structure underwent substantially more deformation and stress in the broadened sections. The mean values of the surrounding rock’s horizontal convergence and vault settlement in the broadened section were 15.71% and 16.36% higher than those in the general section, respectively, and the value of lining stress was 35.51% higher. Additionally, the simulation results under the improved construction measures matched the measured results. The maximum deformation and stress of the surrounding rock were reduced by 16.95% and 40.04%, respectively, under the improved scheme, while the lining stress was reduced by 45.38%. The stress state of the secondary lining was significantly improved; in particular, the tensile stress in the lining structure under the original construction scheme was converted into a compressive state under the new measures, fully utilizing the bearing effect. Finally, the rationality and effectiveness of the adopted reinforcement measures were evaluated, and the experiences and lessons learned were summarized to provide insights for preventing similar incidents from reoccurring.

/pdf/investigation-into-the-large-deformation-mechanism-and-2w3nxoet.pdf

Investigation into the Large Deformation Mechanism and Control Technology of Variable Cross-Section Tunnel in Layered Mudstone Stratum

This paper introduces a new type of prestressed uplift pile that adopts the semi-bonded composite anchor as the main reinforcement. An in-situ experimental study was carried out to investigate the new pile’s deformation, stress, bearing capacity, and cracking characteristics, which were then compared with the conventional piles. Results show that although the reinforcement ratio of the new pile is only 0.75%, much less than that of the conventional pile (i.e., 3.84%), it achieves similar or even better mechanical properties under uplift loads. The cost of the pile’s anchorage system is reduced by 43.8%, and the total cost of a single pile is reduced by 33.6%. Compared with the conventional pile, the new pile makes better use of the lateral friction resistance of the lower pile body, and the uplift bearing capacity and the uplift resistance of the pile are improved correspondingly. In addition, the cracking resistance of the new pile is significantly improved, with the cracking load increased by 88.2% and the cracking area reduced by 48.3%. In addition, the multi-layer structure of the composite main bar provides better protection for the load-bearing steel strands against corrosion. As such, the new type of pile is expected to gain much better durability than the conventional ones.

/pdf/development-of-a-new-uplift-pile-with-prestressed-semi-3tpyeicd.pdf

Development of a New Uplift Pile with Prestressed Semi-Bonded Composite Anchor

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Investigation into the Large Deformation Mechanism and Control Technology of Variable Cross-Section Tunnel in Layered Mudstone Stratum

Development of a New Uplift Pile with Prestressed Semi-Bonded Composite Anchor