Experimental Determination and Constitutive Modeling of Time Effects in Sand

沙中时间效应的实验测定和本构模型

• 批准号: 1130203
• 负责人: Poul Lade
• 金额: $ 33.2万
• 依托单位: Catholic University of America
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1130203&HistoricalAwards=false
• 关键词: Experimental; Determination; Constitutive; Modeling; Time

Time effects in soils such as creep and relaxation cause long-term deformation and pressures on buildings, bridge abutments, earth retaining structures, and in slopes. Excessive deformation with time may cause structures to fail. While creep and stress relaxation are caused by the same phenomenon, namely grain crushing followed by grain rearrangement, the prediction of one phenomenon can apparently not be accomplished on the basis of the other. Several series of high pressure triaxial compression tests will be performed to study strain rate effects, creep, and stress relaxation on Virginia Beach sand. Thus, the time to fracture of these particles depends on the proximity of the stress state to the short-term fracture strength. Once fracture takes place, rearrangement of the grain structure will occur due to sliding and rolling of grains. Each of these types of mechanical behavior are time dependent, and together they constitute the phenomena of time effects in sand. This is quite different from the viscous effects seen in clays.The proposed research will contribute to establishment of more realistic modeling of sand behavior as it occurs in-situ. Real sands show time effects as they are deposited or loaded to higher stresses or if they are disturbed, thus creating fresh contacts between the particles. This real time behavior is most often assumed to be nonexistent, and a number of observed behavior patterns of geotechnical structures are therefore not predicted correctly. The benefits of the proposed research to society will be improved predictions of the behavior of geotechnical engineering structures and soil-structure interaction as well as consequent greater safety and economy of construction.

蠕变和松弛等土壤中的时间影响会导致建筑物，桥梁基台，地球固定结构和斜坡的长期变形和压力。时间过度变形可能导致结构失败。虽然蠕变和压力放松是由相同的现象引起的，即颗粒粉碎，然后是晶粒重排，但显然不能基于另一个现象来实现一种现象。将对弗吉尼亚海滩沙滩上的应变率效应，蠕变和压力放松，进行几种高压三轴压缩测试。因此，这些颗粒断裂的时间取决于应力状态与短期断裂强度的接近度。一旦发生断裂，由于谷物的滑动和滚动，晶粒结构将重新排列。这些类型的机械行为都取决于时间，它们共同构成了沙子中时间效应的现象。这与粘土中的粘性作用完全不同。拟议的研究将有助于建立对沙子行为的更现实的建模，因为它发生在原位。实际沙子显示时间效应，因为它们被沉积或加载到更高的应力或受到干扰时，从而在颗粒之间产生新的接触。这种实时行为通常被认为是不存在的，因此无法正确预测岩土结构的许多观察到的行为模式。拟议的研究对社会的好处将改善对岩土工程结构和土壤结构互动的行为的预测，以及随之而来的更大的安全性和建筑经济。