Study on Four-Dimensional Coupling Evaluation and Graded Dynamic Support Methods for Surrounding Rock Softening in High-Stress Soft Rock Roadways of Kilometer-Deep Mines

Deformation failure mechanism of deep high-stress fractured soft rock roadways and active-passive full-space collaborative control technology.

Controlling the stability of deep high-stress fractured soft rock roadways is a key scientific issue in mining engineering. Using the south wing return-air roadway at the - 650 level of Yangcheng Coal Mine as the engineering background, this study performed mechanical property tests, mineral composition analysis, and in-situ stress tests on the surrounding rock. It further investigated the failure mechanisms and control strategies from the perspectives of lithology and stress environment. The results indicate that the main causes of large deformation in the roadway are: high in-situ stress, high clay mineral content (> 50%) in the soft surrounding rock, superimposed mining-induced stress, and the lack of coupling between the support structure and the surrounding rock. We proposed an active-passive full-space collaborative control technology consisting of concrete-filled steel tubular supports, bolt-mesh-shotcrete, and surrounding rock grouting. Using similar simulation, we investigated the stress distribution of the surrounding rock, deformation characteristics of support structures, load-strain response of supports, and displacement evolution of the surrounding rock under coupled static-dynamic loading. The results demonstrate the excellent bearing performance of concrete-filled steel tubular supports under high static loads and strong disturbances. Field monitoring results show that the maximum roof subsidence was 51 mm, floor heave 106 mm, and side convergence 77 mm. These data indicate that the deformation and failure of the surrounding rock have been effectively controlled. This study provides a theoretical basis and technical support for surrounding rock control in deep, high-stress, fractured soft rock roadways.

Study on the Interaction Between Surrounding Rock and Support in High-Stress Soft Rock Roadways Based on Rock Rheological Properties

High-stress soft rock roadways in deep underground engineering often exhibit significant time-dependent deformation due to strong rheological behavior of surrounding rock. To investigate the deformation characteristics and support effect, a composite viscoelastic constitutive model considering anchored and unanchored rock zones is established based on the Maxwell rheological framework. The equivalent stiffness contribution of rock bolts is incorporated to characterize the interaction between support and surrounding rock. Analytical solutions of radial displacement and creep rate are derived using viscoelastic theory and Laplace transform methods. The effects of bolt spacing, bolt length, and burial depth on the rheological response are analyzed. Numerical simulations based on FLAC3D creep analysis and field monitoring data are used to verify the proposed model. Results show that decreasing bolt spacing effectively reduces long-term deformation, while bolt length has a diminishing effect beyond a critical anchorage length. Increasing burial depth significantly increases creep rate and total deformation. The numerical results agree well with theoretical predictions (R2 ≈ 0.985), and field measurements show a relative error within 10%. The proposed model effectively describes the long-term deformation trend of high-stress soft rock roadways and provides a theoretical reference for support design under similar conditions.

Surrounding Rock Deformation Mechanisms and Control in Deep Mining: A Comprehensive Review

Study on spatiotemporal evolution law of surrounding rock stress in deep high-stress soft rock roadways.

To address large deformation and support failure in deep, high-stress soft-rock roadways, this study investigates the - 810 m track main roadway of Pansan Coal Mine using fiber Bragg grating three-dimensional stress monitoring and borehole fracture observation, combined with FLAC3D numerical simulations. Results show that the maximum principal stress gradually transfers to the deep surrounding rock with increasing roadway distance, while the shallow rock undergoes continuous unloading, promoting plastic zone expansion and eventual instability. Timely reinforcement of the shallow surrounding rock is critical to forming an integral load-bearing system with the deep rock mass. The spatiotemporal effect of principal stress evolution is identified as the fundamental cause of roadway failure, providing theoretical and practical guidance for deep roadway support design.

Stress Distribution and Evolution Characteristics of Hard–Soft Interbedded Floor Strata Subjected to Coal Pillar Loading

To reveal the stress transfer mechanism of overlying coal pillar loads in hard–soft composite floor strata during close-distance coal seam mining, this study comprehensively employed theoretical analysis, similar material simulation, and numerical simulation to systematically investigate the floor stress distribution characteristics under different pillar widths and rock combinations. This study focuses on the instantaneous elastic response of hard–soft composite floor strata under static coal pillar loading, providing a theoretical foundation for pillar design and roadway layout in multi-seam mining. The limitations and future research directions are also discussed. First, based on the elastic layered half-space theory, mechanical models for stress transfer in the floor under narrow coal pillars (unimodal load) and wide coal pillars (bimodal load) were established. Analytical expressions of stress at any point in the floor were derived, and the influence laws of key parameters, including Poisson’s ratio, interlayer spacing ratio, and shear modulus ratio, were clarified. Second, two typical physical models, namely “hard–soft–hard” and “soft–hard–soft”, were constructed. Experimental results revealed that the weak interlayer exhibits a significant “barrier effect” in the hard–soft–hard combination, causing the stress contours to contract in a “bulb-like” shape; whereas the hard rock layer plays a “bearing effect” in the soft–hard–soft combination, leading to stress contours diffusing in a “gourd-like” shape. Furthermore, numerical simulation revealed the controlling mechanisms of rock combination and thickness ratio: the hard rock layer dominates stress concentration, with the peak stress zone evolving from an “inverted water droplet” shape to a “platform” shape as the thickness increases; the soft rock layer governs stress diffusion and buffering. The depth of the plastic zone significantly decreases with increasing hard rock thickness ratio, achieving a reduction of 44.4%.

Failure mechanism of gob-side entry in weakly cemented soft rock and bolt-grouting collaborative control method: a case study.

During coal mining in western China, soft rocks with low strength, poor cementation, and a tendency to disintegrate upon water exposure are often encountered. This makes bolt support unable to maintain long‑term roadway stability, resulting in severe roadway deformation and failure. To solve this challenge, this manuscript combines theoretical research, numerical simulation, and field measurements. Firstly, the characteristics of weak cementation and low strength of weakly cemented soft rock were obtained through experiments. Combined with the field‑monitored features of large‑scale roof fracturing and failure in gob‑side roadways, the support failure mechanism was revealed: poor support effectiveness caused by surrounding rock fracturing in the anchored section of roof bolts. Secondly, the tangential stress around the rectangular roadway was obtained through theoretical calculation, and it was found that roadway width and lateral pressure coefficient are the main factors affecting surrounding rock deformation. Numerical simulation revealed that as roadway width and lateral pressure coefficient increase, the plastic zone in the roof strata expands laterally and into deeper areas. Finally, the mechanical properties of different grout consolidation bodies were investigated, and the grouting effects under different grouting ranges were obtained. A bolt‑grouting collaborative support method was proposed. Field tests showed that the roof‑to‑floor convergence was reduced by more than 60%, indicating good support performance.