A Study of Finite Strain Consolidation Aspects of Soft Soils

这项建议解决了岩土工程中相当感兴趣的一组问题中的一个具体问题。这组问题都与发展土的一般应力-应变-时间理论有关，例如，发展本构模型。解决任何土体应力状态改变的问题都需要这样一个模型，我们需要估计变形，例如当我们建造建筑物、桥梁、大坝等时。这项研究要解决的具体问题是分析打入桩基础周围土壤中发生的随时间变化的情况。桩是一种细长的结构构件，被打入地下，用于为结构提供支撑。打桩在桩附近的土壤中引起大应变，并导致土壤性质的大变化，这些变化是从桩向外径向变化的。此外，在填满土壤非固体部分的水中产生过多的压力，然后这些水以一种与时间相关的方式向外流动。当水流动时，土壤会变得更坚固，从而导致桩的承载能力增加。工程师在设计地基时指望这种增加的能力，但如果能力建立得太慢，或者施工太快，地基就有可能出现故障。这一问题在海上石油生产结构中尤其严重，这些结构的桩直径可能高达10英尺，长度可能超过2000英尺，每根桩的设计承载能力高达5000吨。对于如此大的桩，没有任何载荷测试在经济上是可能的，所以设计是基于对小桩的测试，并辅之以理论。这项建议主要涉及这个问题的理论部分。该研究的理论部分包括建立一个通用模型来描述深基础附近土体对基础安装和随后加载所引起的条件变化的时变响应。还有一个实验部分，主要研究人员将用小型渗透仪进行测试，以模拟桩的作用。这项研究的另一个方面是通过分析找出必须存在的土壤特性，以解释贯入仪的性能。

This proposal address a specific problem within a group of problems of considerable interest in geotechnical engineering. The group of problems all relate to efforts to develop a general stress-strain- time theory for soils, e.g., to develop a constitutive model. Such a model is required for solution of any problem in which the state of stress in soil is changed and we need to estimate deformations, e.g., when we construct buildings, bridges, dams, etc. The specific problem to be addressed by this research is the analysis of what happens in soils around driven pile foundations as a function of time. Piles are long thin structural members that are driven into the ground and used to provide support for structures. Driving of the piles causes large strains in the soils in the vicinity of the piles and results in large changes in soil properties which, vary radially outwards from the pile. Further, excess pressures develop in the water filling the non-solid parts of the soil, and this water then flows outwards in a time-dependent fashion. As the water flows, the soils densify and become stronger, thus causing an increase in the load capacity of the piles. Engineers count on this increased capacity when they design the foundation, but if the build up in capacity is too slow, or the construction too fast, it is possible to have failures in the foundations. The problem is particularly severe with offshore oil production structures where piles may be up to ten feet in diameter and more than 2000 feet long, and be designed to carry loads of as much as 5000 tons per pile. No load testing has ever been economically possible for such large piles so the design is based on tests on small piles augmented by theory. This proposal is concerned mainly with the theoretical part of this problem. The theoretical part of the study involves an attempt to develop a general model to describe the time-dependent response of the soil near deep foundations, to the changed conditions caused by the installation and subsequent loading of the foundation. There is also an experimental part in which the principal investigators will perform tests with small penetrometers to simulate the action of a pile. Analyses to find the soil properties that must have existed in order to explain penetrometer performance is another aspect of this research.