In urban regions with karst developments, grouting is commonly utilized to fill cavities. However, the extent and control standards of grouting reinforcement are primarily determined through experience and field testing, which poses challenges in ensuring its effectiveness. Based on the instability mechanism of surrounding rocks in underwater karst shield tunnels, this study develops a mechanical model for analyzing the grouting reinforcement extent of such tunnels using strength theory. The reinforcement range for karst formations at various tunnel locations is clarified, and corresponding grouting reinforcement control standards are proposed based on cusp catastrophe theory. The findings indicate the following: the primary cause of surrounding rock instability in underwater karst shield tunnels is that the reduction in surrounding rock thickness during shield tunneling modifies the original constraints and boundary conditions and disrupts the initial equilibrium state. These changes influence the water content of the surrounding rocks and disturb the surrounding rock and soil mass, leading to surrounding rock instability. When grouting causes damage to the surrounding rocks between the karst and tunnel, the system is simplified into cantilever beam and plate models for analysis. It is determined that the grouting reinforcement extent is primarily influenced by factors such as karst size, properties of the karst filling material, and tunnel span. The total potential energy of the rock mass between the karst and tunnel is calculated, leading to the development of an instability and catastrophe model for the surrounding rocks. The proposed grouting reinforcement control standards are mainly dependent on factors such as the distance of the karst, characteristics of the reinforced surrounding rocks, shield machine support force, material properties post-reinforcement, and karst size.

The issue of water-enriched surrounding rock induced by excavation disturbances in loess tunnels represents a significant challenge for the construction of loess tunnel projects. Based on the concepts of lime sac water absorption, expansion, and compaction, consolidation, and drainage of surrounding rock and soil, as well as active reinforcement, a tandem water-absorbing and compaction anchor with heat-expansion and compaction consolidation functionality has been developed. To facilitate the engineering design and application of this novel anchor, a consolidation equation for cylindrical heat source-consolidated soil was derived under conditions of equal strain and continuous seepage. Considering the impact of temperature in the thermal consolidation zone on soil permeability, an analytical solution for the average degree of consolidation of the surrounding soil after support with the water-absorbing and compaction anchor was provided. The correctness of the solution was verified through engineering examples, demonstrating the reasonableness of the theoretical calculation method used in this study. The analysis of consolidation effects in engineering examples demonstrates that the excess pore water pressure in the borehole wall area dissipates rapidly after reaming, exhibiting an exponential decay over time. By the 100th time step, the pore pressure decreases from 100 kPa to 63.2 kPa. As consolidation continues, by the 1000th time step, the pore pressure further reduces to 21.6 kPa. The region with significant changes in pore pressure amplitude is primarily located within the plastic zone of the reamed hole, while the rate of pore pressure change in the more distal elastic zone is generally lower. The consolidation process effectively dissipates the excess pore water pressure and converts it into effective stress in the soil, indicating a notable active reinforcement effect of the water-absorbing compaction anchor. Within the plastic zone, the attenuation rate of excess pore water pressure is 85%. Under different drainage conditions at the borehole wall, the dissipation rate of excess pore pressure in Model 1 (Assuming drainage conditions around the water absorbing anchor rod) is greater than that in Model 2 (Assuming that there is no drainage around the water absorbing anchor rod), with the average degree of consolidation in Model 1 being 22% higher than in Model 2. Under the conditions of Model 1, the active reinforcement effect of the water-absorbing compaction anchor is more pronounced, providing better reinforcement for the surrounding rock and soil. To ensure the reinforcement effect, the theoretical design should consider a certain surplus in the filling quality of the lime water-absorbing medium. The research findings are of significant importance for advancing the theoretical structural design and engineering practical application of this new type of anchor.

Understanding the deformation mechanism and behaviour of adjacent tunnels subjected to dynamic train loads provides vital technical insights for engineering design. This study conducted a detailed analysis and revealed that tunnel excavation significantly affects the stability of adjacent existing tunnels under dynamic loads. First, we developed a dynamic load simulation approach and derived a calculation formula for shield-soil friction. A methodology for analyzing the stress in the surrounding rock of the tunnel was established. Subsequently, the impact of dynamic loads on the stability of existing tunnels was assessed through numerical simulations. Finally, the numerical results were compared with field-measured data to validate the reliability of the research findings. The results indicated that, compared to the condition without train load, the maximum vertical and lateral displacements at the vault of the existing tunnel under dynamic load condition increased by 2.9 mm and 1 mm, respectively, leading to an overall safety and stability coefficient reduction of approximately 0.1. Furthermore, the influence of dynamic loads on the stability of the existing tunnel intensified with increasing train speeds under various load conditions. For train speeds of <= 40 km/h, the dynamic load could effectively be considered as a static load. Notably, the surrounding soft rock exhibited a higher degree of stress release compared to the surrounding hard rock. The stresses at the soft-hard rock interface were found to potentially induce damage to the tunnel. In scenarios where new and existing tunnels were in proximity, the dynamic load was incorporated into the entire simulation process, yielding results that closely aligned with actual measurements.

To investigate the asymmetric deformation and stress characteristics of tunnels and support structures in high geostress layered fractured rock, this paper establishes two refined modeling methods: a numerical model for anchor bolt failure and a model for fractured layered surrounding rock, while considering the spatial variability of soil. The study analyzes tunnel deformation and bolt tensile-shear fracture mechanics under varying bedding angles. The results indicate that: (1) the most unfavorable stress position for tunnel structures in layered fractured rock typically occurs normal to the bedding planes; (2) the tunnel's asymmetric deformation is due to normal compressive and tangential sliding effects of geostress on the bedding planes. When the bedding angle is gently inclined, significant extrusion deformation occurs at the tunnel crown and invert; when steep, substantial tangential sliding forces cause maximum deformation at points where the bedding direction is tangent to the tunnel profile. (3) Fracture development in the surrounding rock primarily occurs normal to the foliation planes, similar to maximum displacement deformation patterns, while other areas propagate outward due to joint shear slip. (4) In layered fractured rock, failed bolts predominantly show tensile-shear fractures, influenced by bedding angle, particularly near the left shoulder to the crown and right invert. Finally, based on the deformation characteristics of layered fractured surrounding rock and the mechanical properties of anchor rod fracture, reasonable differential support optimization measures were proposed, and the simulation results were applied to the Yangjiaping Tunnel of the Chenglan Railway in China.

Backfill is often employed in mining operations for ground support, with its positive impact on ground stability acknowledged in many underground mines. However, existing studies have predominantly focused only on the stress development within the backfill material, leaving the influence of stope backfilling on stress distribution in surrounding rock mass and ground stability largely unexplored. Therefore, this paper presents numerical models in FLAC3D to investigate, for the first time, the timedependent stress redistribution around a vertical backfilled stope and its implications on ground stability, considering the creep of surrounding rock mass. Using the Soft Soil constitutive model, the compressibility of backfill under large pressure was captured. It is found that the creep deformation of rock mass exercises compression on backfill and results in a less void ratio and increased modulus for fill material. The compacted backfill conversely influenced the stress distribution and ground stability of rock mass which was a combined effect of wall creep and compressibility of backfill. With the increase of time or/and creep deformation, the minimum principal stress in the rocks surrounding the backfilled stope increased towards the pre-mining stress state, while the deviatoric stress reduces leading to an increased factor of safety and improved ground stability. This improvement effect of backfill on ground stability increased with the increase of mine depth and stope height, while it is also more pronounced for the narrow stope, the backfill with a smaller compression index, and the soft rocks with a smaller viscosity coefficient. Furthermore, the results emphasize the importance of minimizing empty time and backfilling extracted stope as soon as possible for ground control. Reduction of filling gap height enhances the local stability around the roof of stope. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Moraines, characterized by the accumulation of rock and soil debris transported by glacial activity, present unique challenges for tunnel construction, particularly in portal sections, due to prevailing geographical and climatic conditions that facilitate freeze-thaw action. Despite these challenges, there is a dearth of studies investigating the influence of freeze-thaw action and water content on the mechanical properties of moraines, and no research on calculating surrounding rock pressure in moraine tunnels subjected to freeze-thaw conditions. In this study, direct shear tests under freeze-thaw cycles were conducted to examine the effects of freeze-thaw cycles and water content on the mechanical properties of frozen moraine. A comprehensive parameter K, integrating the number of freeze-thaws and water content, was introduced to model cohesion c. Drawing on Terzaghi Theory, we propose an improved algorithm for calculating surrounding rock pressure at the portal of moraine tunnels. Using a tunnel as a case study, surrounding rock pressure was calculated under various conditions to validate the Improved Algorithm's efficacy. The results show that: (1) Strength loss exhibits a linear trend with the number of freeze-thaw cycles at water content levels of 4% and 8%, while at 12% water content, previous freeze-thaw cycles induce more significant damage to the soil. (2) Moraine saturation peaks between 8% and 12% water content. Following repeated freeze-thaw cycles, moraine shear strength initially increases before decreasing with varying water content. (3) The internal friction angle of moraine experiences slight reductions with prolonged freeze-thaw cycles, but both freeze-thaw cycles and water content significantly influence cohesion. (4) Vertical surrounding rock pressure increases after the initial freeze-thaw cycle, particularly with higher water content, although freeze-thaw cycles have minimal effect on it. (5) Freeze-thaw cycles lead to a substantial increase in lateral surrounding rock pressure, necessitating reinforced support structures at the arch wall, arch waist, and arch foot in engineering projects to mitigate freeze-thaw effects. This study provides a foundation for designing and selecting tunnel support structures in similar geological conditions.

This study analyzes the stability of surrounding rock for a circular opening based on the energy and cavity expansion theory, and regards the surrounding rock failure of circular opening as an unstable state driven by energy. Firstly, based on the large-strain cylindrical cavity contraction and energy dissipation method, the deformation caused by the excavation of surrounding rock is regarded as the cylindrical cavity contraction process. By introducing the energy dissipation mechanism, the energy dissipation solution of cylindrical cavity contraction is obtained. The energy dissipation process of surrounding rock is characterized by the strain energy changes in the elastic and elasto-plastic regions of this cavity contraction analysis. Secondly, the deformation control effect of support and surrounding rock parameters on the energy dissipation of surrounding rock is studied based on the energy dissipation solution of surrounding rock under support conditions. Finally, the effectiveness and reliability of the analytical approach was demonstrated by comparing the support design results with those in the literature. The research results indicate that the three-dimensional mechanical properties and dilatancy angle of rock and soil mass have a significant impact on the energy support design of surrounding rock. This study provides a general analysis method for the stability analysis of surrounding rock of deep buried tunnels and roadway.

To solving the engineering problems of tunneling in backfill soils, the shallow buried concealed excavation of the northern line of the Zengjiayan Bridge Tunnel Project in Chongqing has been taken as the relying project and numerical analysis and monitoring have been used to study on deformation characteristics of surrounding rock in small clearance tunnel excavation in backfill soil layer. The result of this study reveals that: firstly, during the excavation the maximum surface settlement will move from the top of the advance tunnel to the top of the intermediate rock pillar. Secondly, the surrounding rock deformation pattern of the backward tunnel could be described as: predeformation-sharp deformation- deformation convergence, and the surrounding rock deformation pattern of the advance tunnel could be described as: predeformation-sharp deformation- first deformation convergence- additional deformation- final deformation convergence. Thirdly, the excavation of the advance tunnel will lead to the predeformation in vault, arch and the side wall of the backward tunnel, and the excavation of the backward tunnel will lead to the additional deformation in the same places of the advance tunnel. The conclusion of this study is consistent with the existing research and can provide reference for similar projects.