Simplified analysis of consolidation for water-absorbing compaction anchor support in weak and water-rich soil surrounding rock

Abstract 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.