A series of laboratory-based water infiltration tests at room temperature have been conducted to investigate the mechanical characteristics of Heishan bentonite as a potential backfill material. The experiments were performed with an oedometer testing apparatus which facilitates the mechanical loading, the water infiltration, and the deformation measurement. The results show that both swelling pressure-initial dry density and swelling strain-moisture content have an exponential relationship. Moreover, swelling strain dramatically decreases when the applied stress exceeds a reference stress of 100 kpa. Finally, permeability tests were carried on Heishan bentonite specimen and the studied material reaches an impermeable state when the moisture content is larger than 40%. The presented properties certificate that Heishan bentonite can be employed as a backfill material in engineering practice.
Taking into account the high cost of damage to structures caused by uneven ground movements associated with expansive soils, the mechanical behavior of these materials is critically important to be studied theoretically and experimentally. A simplified constitutive model is proposed based on a 1-D mechanical design containing a parallel connection of the linear spring and the dashpot element, and its mathematical formation is presented in terms of the physical mechanism. The procedure of model parameters is introduced using cyclic suction-controlled tests by an expansive soil in France and a silt-bentonite mixture. The comparison between model simulations and tests is accomplished and this comparison explains that the simplified constitutive framework can describe basic features of expansive soils under wetting and drying cycles.
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