土工离心试验应力相似差异特征与设计准则

Difference characteristics of stress similitude for geotechnical centrifuge modelling and design criteria

土工离心试验优越性的基础在于建立模型与原型相同的应力条件与分布,认识模型与原型之间应力相似差异与表征参数对控制系统误差和优化设计参数具有重要指导价值。引入总体分布应力、附加侧向应力和耦合动应力3个新概念与定义,对模型与原型之间应力差异特征、表征参数和设计准则等进行了深入研究。总体分布应力采用应力误差描述,表征参数为模型高度H和最大半径maxR;当maxH/R≤0.3和0.15,可控制模型极限应力误差≤10%和5%。附加侧向应力由模型中心剖面向两侧宽度增大分布,由模型宽度b、有效半径efR和有效离心加速度efa决定大小;以100 kPa为标准,给出了不同离心加速度下有效半径与允许模型设计宽度关系。耦合动应力影响采用目标与额外应力比进行评价,以efR和角速度？为表征参数,给出了应力比以10%和20%为标准的efa-efR的临界关系曲线;当efa≥10g、efR≥4 m时,耦合动应力的影响可以忽略。研究提出的新概念、表征参数和设计准则,为改进设备、模型参数设计和推动量化研究提供研究基础与参考依据。

The advantage of geotechnical centrifuge modelling is founded on the exactly similar stress levels and distribution between models and prototypes. To recognize the differences and characterization parameters of stress similitude of model and prototype is of significant value to decreasing systematic errors and optimizing design parameters. Three new concepts of general distributed stress, additional lateral stress and coupling dynamic stress are proposed and defined, by using which the difference characteristics, characterization parameters and design principles of model stress compared to those of prototype are studied. The general distributed stress is represented by the stress error referring to the model height H and the maximum radius maxR, and as maxH/R ≤0.3 and 0.15, the stress error limits of soil model are less than 10% and 5%. The magnitude of additional lateral stress increases from center section to two width boundaries, and is mainly governed by the model width b, effective radius efR and effective centrifugal acceleration efa. Selecting 100 kPa as a criterion, the allowable model width limits with varying effective radius for different centrifugal accelerations are proposed. The influence of coupling dynamic stress is evaluated through the ratio of the target stress to the extra stress involving two key parameters of efR and angular velocity . With 10% and 20% as the criteria of the stress ratio, the critical curves of efa-efR are obtained and if efa ≥10 g and efR ≥4 m, the influence of coupling dynamic stress can be ignored. The proposed new concepts, characterization parameters and design criteria provide the reference and basis for the parametric design of facilities and soil models and development of quantitative researches.