地盤材料の変形特性に対する時間効果の新しい展開

对更新世粘土、砂砾、沉积软岩和水泥混合土等刚性土质在卸载条件下的变形特性进行了理论和实验研究。这种特性的正确预测对于许多实际问题都很重要，例如预压效果的评估、开挖后地基的随时间变形和现场加载试验中卸载特性的解释。从本研究中，对各种刚性土工材料进行试验，得到了以下共同的结论：1)即使从某一加载状态以恒定加载速率开始卸载，变形的增加仍以减小的速率继续增加。2)当荷载水平降低到一定水平时，不可逆变形率变为零。(3)当载荷水平进一步降低时，不可逆变形率变为负值，蠕变阶段变形率随时间减小，松弛阶段载荷随时间增大。现有的土工材料变形特性的时间效应理论大多只考虑加载阶段的变形。鉴于上述，我们建立了以下本构模型来解释上述问题。1)新的等距模型；将给定的应变增量分解为弹性分量和不可逆分量，将给定的应力分解为无粘分量和粘性分量。定义了加载、卸载等过程中非粘应力与不可逆应变之间的滞后关系。然后，给定应力历史的当前应力状态由瞬时不可逆应变及其速率唯一地控制。该模型适用于几种类型的粘土和沉积软岩。2) TESRA（应变率和加速度的临时效应）模型：对不可逆应变积分得到当前粘性应力，即不可逆应变增加的粘性应力增量和不可逆应变速率增加的粘性应力增量。在这个积分中，考虑了这两种类型的粘性应力增量随不可逆应变的衰减。该模型适用于差级配砂。少

The time effects on the deformation characteristics under unloaded conditions of stiff geomaterials, such as Pleistocene clays, sand/gravel, sedimentary soft rock and cement-mixed soils, were studied theoretically and experimentally. The proper prediction of this behavior is important for many practical issues, such as evaluation of preloading effects, time-dependent deformation or ground subjected to excavation and interpretation of the unloading behavior in the field loading tests. From the present study, the following conclusions were obtained commonly with various stiff geomaterials tested in the present study :1) Even after unloading is started at a constant load rate from a certain loaded state, the increase in the deformation continues at a decreasing rate.2) When the load level is decreased to a certain level, the rate of irreversible deformation rate becomes zero.3) When the load level is further decreased, the irreversible deformation rate becomes negative, while the deformat … More ion decreases with time at a creep stage and the load increases with time at a relaxation stage.Most of the existing theories on the time-effects on the deformation characteristics of geomaterials deal with the deformation during loading stage. In view of the above, the following constitutive models were developed to explain the above.1) New isotach model ; a given strain increment is decomposed into the elastic and irreversible components, while a given stress is decomposed into the inviscid and viscous components. The hysteretic relationships between the inviscid stress and the irreversible strain for loading, unloading and so on are defined. Then, the current stress state for a given stress history is uniquely controlled by instantaneous irreversible strain and its rate. This model is relevant to several types of clay and sedimentary softrocks.2) TESRA (temporary effects of strain rate and acceleration) model : the current viscous stress is obtained by integrating with respect to the irreversible strain the viscous stress increment by the increase in the irreversible strain and that by the increase in the irreversible strain rate. In this integration, a decay of these two types of viscous stress increments with the irreversible strain is taken into account. This model is relevant to poorly graded sands. Less