Energy balance support method in soft rock tunnel with energy absorbing anchor cable

Abstract

Deformation and failure phenomena in rock mass after excavation can be described from the energy perspective, i.e. the work done by external forces increases the energy, thereby exceeding the energy storage limit of rock mass, resulting in the release of residual energy. Currently, energy-absorbing anchor supports have been used for stability control of surrounding rocks to avoid engineering failure by large deformations of soft rocks. However, the design of energy-absorbing anchor support still depends on field experience and engineering tests. In particular, under the influence of structural plane, the characteristics of energy transfer of surrounding rock with energy-absorbing anchorage are still unclear. In this paper, a design method of energy anchorage considering the influence of structural plane based on the theory of energy balance is proposed, which is corroborated by numerical simulation, similar simulation, and engineering application. The study demonstrates that under the effect of ground stresses, the arch support alone cannot absorb the deformation energy produced by the surrounding rock, leading to a significant region of the plastic zone and deformation instability. Under the control of ordinary anchor cable, the deformation of surrounding rock and the extension of the plastic zone are further alleviated; however, some anchor cable tensile fractures still occur. The energy-absorbing anchor cable scheme is created following the energy balancing concept. The surrounding rock deformation is maintained in an ideal range, while the plastic zone area is substantially reduced. The final engineering application also validates the accuracy of the energy-absorption anchorage design based on the energy balance theory, which provides a theoretical and practical basis for the application in similar projects.