Axisymmetric centrifuge modelling of deep penetration in sand to model driven piles or the cone penetration test

沙中深度贯入的轴对称离心机建模，用于模拟打入桩或锥入探试验

• 批准号: EP/D064112/1
• 负责人: Edward Ellis
• 金额: $ 20.14万
• 依托单位: University of Nottingham
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FD064112%2F1
• 关键词: Axisymmetric; centrifuge; modelling; deep; penetration

The advancement of a slender object (a 'probe' or 'penetrometer') into soil (to depths of 10s of metres) is of fundamental interest to Geotechnical Engineers. A 'piled' foundation which is fabricated (as a long cylinder) at the ground surface and 'driven' into the ground is an example of such an object, which may be more than a metre in diameter. It may ultimately be used, for example, in the foundation for an offshore structure such as a wind turbine.At the other extreme the 'Cone Penetration Test' (CPT) is used to by Civil Engineers to characterise soils which are at significant depths in the ground by advancing a cylindrical probe which is only few centimetres in diameter. The resistance which the probe encounters in the ground can be 'extrapolated' to design a piled foundation to carry a given load. However, there is still debate regarding exactly how this should be done, reflecting uncertainty of precisely what happens within the soil when a probe (or pile) penetrates the ground to a significant depth.Many problems in geotechnical engineering are relatively well-suited to 'numerical' modelling. However, the rigorous numerical modelling of deep penetration is unusually difficult because the problem involves large deformations and highly nonlinear behaviour. Considerable advances have however recently been made in beginning to understand some detailed aspects of the fundamental behaviour using 'physical' models. The main drawback of such an approach is that the stresses in the soil in the model are much smaller than they would be at (say) 30m depth in the ground for a piled foundation, and this significantly affects the behaviour of the soil. This can be overcome using a 'geotechnical centrifuge' (where the gravitational acceleration is effectively increased so that higher stresses are generated in a small model).Recent advances have also been made in the use of digital photography to 'track' zones of soil as they move (eg. due to an advancing penetrometer). However, this technique has yet to be used in conjunction with an advancing penetrometer in a geotechnical centrifuge model. More particularly, it has not been used with a cylindrical penetrometer (as a pile or CPT would be). Instead a 'plane strain' idealisation has been used, which effectively assumes that the extent of the penetrometer is infinite in one of the horizontal directions.The main emphasis of the proposal is to develop a (half) cylindrical penetrometer and soil physical model which will allow the associated soil movement to be observed. This technique will then be used in a geotechnical centrifuge, utilising digital photography techniques to track movement of the soil. The results will provide fundamental comparison with the 'plane strain' idealisation which is presently used to observe soil movement, and the (full) cylindrical penetrometer, which does not allow soil movement to be viewed. Indeed, the technique would have potential application in all areas of axisymmetric (circular) physical modelling in geotechnical engineering.Use of centrifuge modelling would mean that the results would be applicable to full-scale situations (such as driven piles). The technique would then be used to observe resistance to penetration simultaneously with soil movement, as applied to topical aspects of behaviour such as 'scale effects' for the probe, the influence of a 'layered' soil profile, and the roughness of the probe shaft.

将细长物体（“探针”或“贯入计”）推进到土壤（数十米的深度）是岩土工程师的根本兴趣所在。在地面上制造（作为长圆柱体）并“打入”地面的“堆积”基础就是这种物体的一个例子，其直径可能超过一米。例如，它最终可能用于风力涡轮机等海上结构的基础。在另一个极端，土木工程师使用“锥体渗透测试”(CPT) 来表征位于海洋深处的土壤的特征。通过推进直径只有几厘米的圆柱形探针来探测地面。可以“推断”探头在地面中遇到的阻力，以设计承载给定负载的桩基。然而，关于具体如何做到这一点仍然存在争议，这反映出当探针（或桩）深入地面相当深时土壤内到底发生什么的不确定性。岩土工程中的许多问题都相对非常适合“数值模拟。然而，深穿透的严格数值模拟异常困难，因为该问题涉及大变形和高度非线性行为。然而，最近在开始使用“物理”模型理解基本行为的一些细节方面已经取得了相当大的进展。这种方法的主要缺点是模型中土壤中的应力远小于桩基地下 30m 深度处的应力，这会显着影响土壤的行为。这可以通过使用“土工离心机”来克服（其中重力加速度被有效地增加，以便在小模型中产生更高的应力）。最近在使用数字摄影来“跟踪”土壤区域方面也取得了进展它们移动（例如，由于渗透计前进）。然而，该技术尚未与岩土离心机模型中先进的贯入仪结合使用。更具体地说，它尚未与圆柱形贯入计（如桩或 CPT 那样）一起使用。相反，使用了“平面应变”理想化，它有效地假设贯入计的范围在一个水平方向上是无限的。该提案的主要重点是开发一种（半）圆柱形贯入计和土壤物理模型，它将允许观察相关的土壤运动。该技术随后将用于岩土离心机，利用数字摄影技术来跟踪土壤的运动。结果将提供与目前用于观察土壤运动的“平面应变”理想化和不允许观察土壤运动的（全）圆柱形贯入计的基本比较。事实上，该技术在岩土工程中轴对称（圆形）物理建模的所有领域都有潜在的应用。使用离心机建模意味着结果将适用于全尺寸情况（例如打入桩）。然后，该技术将用于观察与土壤运动同时发生的渗透阻力，应用于行为的局部方面，例如探头的“尺度效应”、“分层”土壤剖面的影响以及探头轴的粗糙度。