【作者】 程钰；

【导师】 周正明；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 岩土工程， 2009， 博士

【摘要】 对于非饱和土土力学的研究,基本上都是围绕吸力这一基本概念开展的。吸力是土体粒间作用力的宏观表现,与土颗粒的尺寸与分布密切相关。土体中颗粒尺寸与分布的随机性,决定了在饱和度变化过程中,土体基质吸力变化的复杂性。因此,描述两者之间关系的土水特征曲线并非一条光滑的曲线,而是一条呈现台阶式起伏的曲线。以往的曲线方程都很少能准确描述土体粒径大小分布与土水特征曲线之间的相似和对应关系。土颗粒的粒径与基质吸力之间存在一定的倒数关系,土颗粒粒径越小、基质吸力就越大,反之亦然。然而,土颗粒的尺寸并不会趋近于无限小,存在一个最小极值。因此,土体的基质吸力也存在最大极值。本文在此基础上建立了一个全新的土水特征曲线方程。颗粒间一切能有效提高土体抗滑能力的因素都称之为广义吸力,基质吸力只不过是其中的一个重要部分。随着饱和度的降低至零,土体间的基质吸力会趋向于一个很大的值,此时土体的强度却不可能趋向于一个很大的值。也就是说,在此过程中只有一部分吸力对强度发挥了作用。因此,从广义吸力丧失的观点出发研究非饱和土的强度是非常有益的。本文就是通过研究基质吸力和结构凝聚力两部分对强度的贡献,建立了非饱和土剪切强度方程,该方程可以较准确的反映砂性土和粘性土的强度特性。非饱和湿胀性土与湿陷性土分别具有亚稳态孔隙比结构和超稳态孔隙比结构,广义吸力是维持这种结构的主要因素。随着广义吸力的丧失,两者均处于一个不稳定的孔隙状态,土体会向一个稳定孔隙比的状态发展。超孔隙比结构产生膨胀,亚稳孔隙比结构的产生收缩。目前还没有一个能够很好解释这一统一变形本质的理论。本文基于稳态孔隙比理论和空间状态面的唯一性原理,通过简单叠加广义吸力丧失产生的孔隙比的增量和净应力压缩作用下的孔隙比增量,建立了能够同时反映湿陷性和湿胀性变形的空间状态面方程。更多还原

【Abstract】 It is known that the variation of suction in unsaturated soil leads to many complexities in soil behavior, for instance, the failure of the effective stress principle. Doubt was therefore cast on the possibility that the suction described traditionally may not be proper both conceptually and mathematically. Attempts are thus made in the thesis to describe the suction in a new way that leads to the establishment of a mathematical formulation for soil-water characteristics, a mathematical formulation for shear strengths and a mathematical formulation for volumetric deformation.The mathematical formulation for soil-water characteristics was derived based on the fact that suction is linked to the pore radius which is linked to the size of soil particles. Therefore the soil-water characteristics curve is related to the particle size distribution curve. Bearing in the mind that the size of soil particles will not become infinite small, i.e., it will reach a certain limit. The particle size distribution curve traditionally cannot reflect this fact, a new particle size distribution curve is therefore proposed. The derived mathematical formulation for soil-water characteristics has two salient features. Firstly, the suction will reach a limit as the degree of saturation reaches zero which remove the unreasonable suction infinity given by many SWCCs in the past. Secondly, the soil-water characteristics curve can have multiple smooth steps if the soil particle size distribution curve has multiple peaks.As the degree of saturation decreases to a certain value, the some soil particles are not completely covered by the water film. The capillary potential force only acts on the water covered part of the soil particle body. In other words, the water-particle interaction area varies as the degree of saturation changes. The true suction needs to reflect the effect of water-particle interaction area reduction. A new theory is thus established for the shear strengths of unsaturated soil to take account of the effect. The derived theory indicates that the shear strength will reach a peak then decrease as the soil dries if the soil is sand. Since the derived theory incorporated the contribution of structural cohesion for clay, the shear strength of unsaturated clay may not have a peak, or it may reach the peak when the soil is extremely dry.The unsaturated soils upon wetting may swell or collapse depending the soil types or void ratio of the soil. The particle structure of the unsaturated soil was considered to be in sub-stable and super stable states depending on the values of the void ratio. Both the sub-stable and super stable states are maintained by the suction. The sub-stable and super stable structure becomes unstable upon wetting because of the suction reduction. There may exist a stable state that neither swelling nor collapsing will happen upon wetting. Employing the concept of stable state void ratio, a general formula was obtained which can describe both the swelling and collapsing behavior of the unsaturated soil.The theories derived were all confirmed to be sensible by the existing experimental results. Some further experimental validations remain to be carried out yet.更多还原