摘要
在传统的土力学中,经常假定剪胀与应力比η存在惟一关系,这与松砂剪缩、密砂剪胀的试验结果不相符,也无法用一种统一的模型模拟无黏性材料在不同初始密度和固结围压条件下的不同特性。另一方面,德鲁克公设不能普遍适用于土体的各种应力、应变情况,需要有新的能量机制作为本构模型的基础。热力学第一定律和第二定律作为自然界普遍适用的规律,能够用来描述能量耗散。在临界状态模型的框架内,将状态依赖剪胀和热力学本构模型结合起来,既考虑剪胀对变形历史中材料内部状态的依赖,又由模型的热力学基础保证屈服面和剪胀函数的协调。通过计算,验证这种状态依赖的热力学模型,结合提出的硬化规律,可以用一组统一的模型参数模拟砂土在不同初始密度和围压下不排水剪切的不同反应。
In classical soil mechanics, dilatancy is often considered as a monodrome function of the stress ratio η for triaxial tests, then plastic flow direction is decided by η uniquely and independent of material＇s internal state. This obviously contracts the observed facts. For two different examples of a kind of sand, one in loose state and the other in dense state, the loose sand contracts while the dense sand dilates when they are subjected to the same shear stress. These two different responses are corresponding to a same η, however, the dilatancies are different, one being positive and the other being negative. If the dilatancy is supposed as a monodrome function of η, the dissimilar characters for cohesionless soil in various initial densities and consolidation pressures cannot be simulated by a unified model. On the other hand, Drucker Postulate cannot satisfy all the conditions for soils, and a new energy dissipation mechanics is needed as the base of constitutive relation. The first and second law of thermodynamics, as the universal rules in the nature, with this point, the corresponding yield locus and flow can be invoked to describe the energy dissipation. Starting rule may be deduced in a systematic manner in terms of the free energy function and dissipation potential function. Within the framework of critical state soil mechanics, a modified model that combines the theory which treats the dilatancy as a state-dependent quantity with constitutive models is presented based on the first and second law of thermodynamics. This model accounts for the dependence of dilatancy on the material internal state during the deformation history, and guarantees the consistence of the dilatancy function with the yield locus because of the thermodynamics basis involved. The simulative capability of model is shown by computing different features under various initial densities and confining pressures in sand triaxial undrained shear test, using the modified model with a unified set of model parameters and the hardening
出处
《岩石力学与工程学报》
EI
CAS
CSCD
北大核心
2006年第7期1316-1322,共7页
Chinese Journal of Rock Mechanics and Engineering
基金
国家自然科学基金资助项目(50479057)
关键词
土力学
剪胀
状态依赖
状态参数
弹塑性模型
热力学定律
soil mechancis
dilatancy
state-dependency
state parameter
elastoplastic model
thermomechanics law
