Three-dimensional visco-elasto-plastic stress-strain-properties at small strains of stiff geomaterials

通过使用先进的三轴和平面应变装置进行特殊测试，研究了硬质岩土材料在三维应力条件下的弹塑性应力-应变特性以及粘性特性（随时间变化的特性）。对硬质粘土、砂土、砾石、粉砂和沉积软岩试样进行了保持不同恒定应变速率、逐步改变恒定轴向应变速率或在多个阶段保持恒定应变速率速率的试验。对于应变小于0.001%时的准弹性应力-应变特性，提出了弹性常数为瞬时应力的特定函数的准弹性模型。在粘性特性方面，发现了与软粘土和粉砂相关的等等线模型。提出了一种简单的等线模型，其中电流应力是瞬时不可逆应变和不可逆应变速率的唯一函数，电流应力增量是瞬时弹性应变增量的唯一函数。研究发现，对于洁净砂，等等线模型不适用，剪切应力和剪切应变关系基本上与恒定应变率无关，其差异可达500倍。当应变速率逐步增大和减小（即给定应变加速和减速的时间史）时，应力水平有明显的暂时升高和降低。同样，随着应变减速的时间历史，砂表现出明显的蠕变变形和应力松弛。

Elasto-plastic stress-strain properties, as well as viscous properties (time-dependent properties), of stiff geomaterials under three-dimensional stress conditions were investigated by performing special tests using advanced triaxial and plane strain apparatuses. Specimens of stiff clays, sands, gravels, silty sand and sedimentary soft rocks were subjected to tests in which different constant strain rates were maintained, the constant axial strain rate was changed stepwise or the rate of strain rate was kept constant at several stages. For quasi-elastic stress-strain properties at strains less than about 0.001%, a hypo-elasticity model was proposed, for which the elastic constants are specific functions of instantaneous stresses. As to the viscous properties, the isotach model was found relevant to soft clays and a silty sand. A simple isotach model is proposed, in which the current stress is a unique function of the instantaneous irreversible strain and irreversible strain rate, and the current stress increment is a unique function of the instantaneous elastic strain increment. It was found that with clean sands, the isotach model is not relevant, and the shear stress and shear strain relationships are essentially independent of constant strain rates differing by a factor up to 500. It was also found that the stress level noticeably and temporarily increased and decreased when the strain rate increased and decreased stepwise (i.e., when a time history of strain acceleration and deceleration was given). Similarly, with a time history of strain deceleration, the sands exhibited noticeable creep deformation and stress relaxation.