Abstract: Bentonite is a clay material dominated by montmorillonite, whose layered structure carries permanent negative charges due to isomorphic substitution. The layer charge is a key factor governing its swelling behavior. In this study, the coupled effects of layer charge and vertical stress on the one-dimensional swelling deformation characteristics of bentonite were systematically investigated through experimental tests and theoretical analysis. Sodium bentonite was used as the base material, and a series of reduced-charge bentonites with progressively decreasing layer charge were prepared using the lithium fixation method. One-dimensional swelling tests were then conducted under different vertical loading conditions. The results show that as the layer charge decreases, the swelling strain of bentonite is significantly reduced and the time required to reach swelling equilibrium is markedly shortened. Meanwhile, vertical loading exerts a pronounced inhibitory effect on swelling deformation, with increasing load leading to a lower swelling magnitude. Moreover, as the vertical load increases, the influence of layer charge on swelling deformation gradually diminishes. By adopting an intergranular stress that can reflect the physicochemical interactions between particles to simulate the above experimental results, it is found that the void ratio-stress relationships of bentonites with different layer charges converge onto a single curve. A single set of parameters can be used to simulate the swelling behavior of bentonite under the coupled effects of layer charge and vertical stress, providing a theoretical basis for the development of a unified chemo-mechanical coupling model.

Key words: layer charge, charge-reduced bentonite, swelling strain, vertical stress, intergranular stress