统一考虑加载变形与流变的粗粒土弹塑性本构模型及应用

实测资料表明,现行粗粒土本构模型明显低估高度200m以上特高土石坝的沉降量,主要原因之一是现行本构模型普遍割裂加载变形与流变,计算时忽略施工过程中坝料产生的流变。在总结分析典型粗颗粒土石料流变特性的基础上,以应力、应变和时间为基本变量,提出了一个可以统一模拟粗粒土加载变形、流变、应力松弛等性质的弹塑性本构模型。模型假定加载塑性变形和流变可同时发生,应力和时间变化均会引起屈服面扩张,从而产生塑性变形,但两者服从不同的塑性流动准则。运用某特高心墙堆石坝坝壳堆石料和砾石土心墙料的试验结果对模型的合理性进行了验证,并对该大坝填筑施工过程进行了模拟。计算结果表明,忽略坝料施工期流变可使大坝竣工期沉降量低估10%以上。因此,采用统一模拟粗粒土加载变形与流变的本构模型可有效提高特高土石坝变形的预测精度。

Elastoplasticity constitutive model considering loading-induced deformation and creep behavior of coarse granular soils and its application

The field observations show that the existing widely-used constitutive models tend to underestimate the settlement of dams higher than 200 m. One of the main reasons is the separation of load-induced deformation and creep in such models and the neglecting of creep during construction in numerical simulations. In this study, a constitutive model, taking the stress, strain and time as the basic variables, is proposed in the light of experimental observations to model the loading deformation, creep and stress relaxation in a unified manner. A basic assumption used is the simultaneous occurrence of the load-induced plastic strains and creep strains. Both the change of stresses and the accumulation of time can result in expansion of the yield surface and thus produce plastic strains to obey, however, different flow rules. The model is used to reproduce the experimental results of a rockfill material and a gravelly soil used in an extremely high rockfill dam, and it is further used to study the deformation behavior of the dam. The numerical results show that neglecting the creep during construction may underestimate the settlement by more than 10%. Therefore, for the extremely high rockfill dams, it is necessary to use the unified models to consider the creep and loading behavior for rockfill materials so as to increase the precision of predictions.