The stability of rock masses in deep underground excavations, such as deep tunnels, shafts, and caverns, critically depends on the mechanical performance of bolt–grout reinforcement systems. In high‐stress and complex geological environments, the interfacial bond–slip behavior between bolts and grouting materials governs the load transfer capacity and long‐term reliability of the support. This study develops an improved shear‐lag analytical model that explicitly incorporates plastic bond degradation, represented through a constant bond stress stage, to capture the complete pull‐out process in four stages: elastic, plastic deformation, debonding, and residual. Closed‐form solutions for the load–displacement response and axial stress distribution along bolts are derived and validated through laboratory pull‐out tests on three types of ribbed bolts embedded in cementitious grout and granite, simulating conditions in deep underground construction. The analytical predictions show excellent agreement with experimental pull‐out tests, capturing both global load–displacement trends and local axial force evolution. Sensitivity analyses indicate that while increasing anchorage length enhances peak capacity, its marginal benefit diminishes beyond a certain threshold. In contrast, the constant bond stress displacement shows a strong positive correlation with the peak pull‐out force, primarily affecting the plastic deformation stage without influencing elastic or residual responses. The proposed model provides a validated, mechanics‐based tool for predicting interface performance in deep underground rock reinforcement systems, offering practical guidance for the design, optimization, and safety evaluation of bonded support in deep mining, hydropower caverns, and large‐span underground spaces.

The performance of resin anchoring agents in deep coal mine roadways is significantly compromised by water-bearing and chemically aggressive conditions, posing a major threat to support system reliability. This study aims to systematically quantify this performance deterioration and develop a more resilient material solution for these challenging environments. A comprehensive experimental program was conducted, including uniaxial compression, pull-out, and interface shear tests, accompanied by the systematic improvement of the resin formulation and microstructural analysis via Scanning Electron Microscopy (SEM). The results showed that increasing borehole water content to 30% reduced the compressive strength of conventional resin by over 40%, while acidic environments (pH = 5) caused a 70% drop in its interfacial shear strength. In contrast, an improved formulation incorporating hydroxypropyl acrylate and a super absorbent polymer (SAP) exhibited a 20% higher initial strength, maintained over 85% of its strength under water saturation, and retained functional residual strength in acidic conditions. SEM analysis confirmed that the improved resin’s denser microstructure suppressed interfacial microcrack formation. The findings demonstrate that the improved formulation provides a robust material basis for enhancing the long-term durability and safety of anchorage support systems in extreme underground engineering environments.