Finite Element Analysis of Expansive Bedrock Considering Electro-chemo-mechanical Coupling Phenomena in Crystal Layers of Clay Minerals and Internal Structural Degradation

Abstract

This research proposes a novel model targeting expansive bedrock by combining an elastoplastic model considering electro-chemo-mechanical phenomena with the Cam-clay model, based on considerations of cementation and its degradation owing to plastic deformation. Additionally, tunnel excavation and swelling analyses are demonstrated by incorporating the proposed model into a finite element analysis code. Specifically, swelling analysis is conducted by decreasing the bedrock ion concentration and by considering the groundwater supply to the tunnel. The simulation results indicate that considerable swelling occurs in a limited area, such as the bottom part of the tunnel, even though changes in ion concentration are uniformly set in the entire analysis area; moreover, swelling phenomena develop instantaneously analogous to the observational records. The simulation reveals that shear stress increases while excavating an area and that softening with plastic expansion occurs in bedrock skeleton owing to decreasing ion concentration. In addition, the yielding of the bedrock skeleton triggers a rapid internal structural degradation and swelling of the clay mineral interlaminar layers based on simulations. Thus, this study clarifies the tunnel swelling deformation mechanism as an interaction problem between coupled electro-chemo-mechanical phenomena occurring in crystal layers and a plastic phenomenon involving the internal structural degradation of the bedrock skeleton.