Microfracture and Repeated Plastic Deformation in Unsaturated Soils as Influenced by Surficial Properties

受表面性质影响的非饱和土中的微破裂和重复塑性变形

• 批准号: 9978672
• 负责人: Robert Lytton
• 金额: $ 25.2万
• 依托单位: Texas A&M Engineering Experiment Station
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-10-01 至 2003-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9978672&HistoricalAwards=false
• 关键词: Microfracture; Repeated; Plastic; Deformation; Unsaturated

***9978672LyttonThis project is to determine how empirical strength and plastic deformationproperties of unsaturated soils are related to more fundamental physical,chemical, and thermodynamic properties of the soil particles, water, and saltsdissolved in the water. The more fundamental properties referred to are theHelmholtz surface energies, wetting and dewetting angles, soluteconcentrations, particle size gradations of the soil particles, and thevolumetric concentrations of soil, water, and air. These are expected tounderlie the fracture and healing properties of the unsaturated soil andexplain the logarithmic work hardening, yield, and plastic potentialcharacteristics of the soil under repeated loading. To the knowledge of theresearch team, there has been little done in the past to make use of theconnection, which has been recently established in polymers, between theviscoelastic characteristics of a soil, the Helmholtz surface energies, and therate of change of dissipated "pseudo-strain" energy in the fracture of thatsoil. In addition, it has recently been discovered that under repeatedloading, the rate of change of dissipated pseudo-strain energy explains theplastic work hardening of a composite material like an unsaturated soil. It isthe purpose of this proposed project to explore these connections infine-grained unsaturated soil to see if the same connections can be made. Itis also proposed here to determine the effect of the osmotic water potential onthe fracture and plasticity properties of a soil. The osmotic potential isrelated to the concentration of organic or inorganic salts dissolved in thepore water. A major effect of the concentration of solute in pore water is toalter the wetting or dewetting angle. It is known that some salts willincrease and other salts will decrease the wetting angle and thus will have adistinctive effect upon the strength of the soil.What makes the measurement of these properties possible is the recentacquisition at Texas A&M of a German-built Universal sorption apparatus and therecent construction of a triaxial unsaturated soil stress path cell withunusually broad capabilities. The first equipment makes it possible to measureall of the components of the Helmholtz surface energies: the Lifshitzvan derWaals apolar components and the Lewis acid and base polar components. Thesecond item of equipment makes it possible to make carefully controlled testson unsaturated soils while measuring all components of mechanical stress andstrain and all components of the water potential over larger ranges than havebeen achieved with similar equipment in the past. The final unique capabilitythat fits these two test apparati together is the ability recently developed atTexas A&M to analyze the test data to determine the dissipated pseudo-strainenergy with each load cycle.***

* 9978672Lytton本项目旨在确定非饱和土的经验强度和塑性变形特性如何与土壤颗粒、水和溶解在水中的盐的更基本的物理、化学和热力学特性相关。 更基本的属性是指的亥姆霍兹表面能，润湿和去湿角，溶质浓度，土壤颗粒的粒度梯度，和土壤，水和空气的体积浓度。 这些结果将有助于揭示非饱和土的断裂和愈合特性，并解释在重复荷载作用下的对数功硬化、屈服和塑性势特性。 据研究小组所知，过去很少有人利用最近在聚合物中建立的土壤粘弹性特征、亥姆霍兹表面能和该土壤断裂时耗散的“伪应变”能变化率之间的联系。 此外，最近发现，在重复加载下，耗散伪应变能的变化率解释了复合材料（如非饱和土）的塑性加工硬化。 本项目的目的是探索细粒非饱和土中的这些连接，看看是否可以建立相同的连接。 本文还建议确定渗透水势对土的断裂和塑性性质的影响。 渗透势与溶解在孔隙水中的有机盐或无机盐的浓度有关。 孔隙水中溶质浓度的一个主要影响是改变润湿角或去润湿角。 众所周知，某些盐会增加润湿角，而另一些盐会减小润湿角，因此对土壤强度有显著的影响，使这些性质的测量成为可能的是最近在德克萨斯州A M获得的德国制造的通用吸附装置和最近建造的具有异常广泛能力的三轴非饱和土壤应力路径单元。 第一台设备可以测量亥姆霍兹表面能的所有成分：Lifshitzvan derWaals非极性成分和刘易斯酸和碱的极性成分。 第二项设备使人们有可能在非饱和土壤上进行仔细控制的测试，同时测量机械应力和应变的所有分量以及水势的所有分量，其范围比过去用类似设备实现的范围更大。 将这两种试验装置结合在一起的最后一种独特的能力是最近在德克萨斯州A M开发的分析试验数据以确定每个载荷循环的耗散伪应变能的能力。*