A Study of Finite Strain Consolidation Aspects of Soft Soils

本提案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。这组问题都与努力发展一般的应力-应变-时间理论有关，例如，发展一个本构模型。这样的模型是解决任何问题，其中土壤的应力状态发生变化，我们需要估计变形，例如，当我们建造建筑物，桥梁，水坝等。本研究要解决的具体问题是分析打入桩基础周围土壤随时间的变化情况。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。桩的打入使桩附近的土体产生较大的应变，并导致土体性质发生较大的变化，这些变化从桩向外呈径向变化。此外，在充满土壤非固体部分的水中产生了额外的压力，然后这些水以一种时间依赖的方式向外流动。随着水流的流动，土体密度增大，强度增大，从而提高了桩的承载能力。工程师在设计地基时就会考虑到这种增加的承载力，但如果承载力的增加速度太慢，或者施工速度太快，地基就有可能出现故障。这一问题在海上采油结构中尤为严重，因为海上采油结构中，桩的直径可能达到10英尺，长度超过2000英尺，每桩的设计承载能力高达5000吨。对如此大的桩进行荷载试验在经济上是不可能的，因此设计是基于对小桩的试验，并辅以理论。这一建议主要涉及这个问题的理论部分。该研究的理论部分涉及尝试开发一个通用模型来描述深基础附近的土壤对由基础安装和随后的加载引起的变化条件的随时间变化的响应。还有一个实验部分，主要研究人员将用小贯深仪进行测试，以模拟桩的作用。为了解释穿透仪的性能，分析发现必须存在的土壤特性是本研究的另一个方面。

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.