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

将细长物体（“探头”或“探土计”）推进土壤（深度为10米）是岩土工程师的基本兴趣。在地面制造（作为长圆柱体）并“打入”地下的“桩”基础就是这种物体的一个例子，其直径可能超过一米。它最终可用于例如海上结构如风力涡轮机的基础中。在另一个极端，土木工程师使用“圆锥贯入试验”（CPT），通过推进直径仅为几厘米的圆柱形探头，对地下相当深的土壤进行渗透。探头在地面上遇到的阻力可以“外推”，以设计一个承载给定载荷的桩基。然而，关于如何准确地做到这一点仍然存在争议，这反映了当探针（或桩）穿透地面到相当深度时，土壤中会发生什么的不确定性。岩土工程中的许多问题都相对适合于“数值”建模。然而，严格的数值模拟深穿透是异常困难的，因为问题涉及大变形和高度非线性行为。然而，最近已经取得了相当大的进展，开始了解一些细节方面的基本行为使用“物理”模型。这种方法的主要缺点是，模型中土壤中的应力远小于（比如）30 m深的桩基，这会显著影响土壤的行为。这可以通过使用“土工离心机”来克服（重力加速度有效地增加，从而在小模型中产生更高的应力）。最近的进展也是在使用数字摄影来“跟踪”土壤移动区域（例如，在土壤移动区域）。由于前进的流速计）。然而，这项技术还没有被用于与先进的离心机模型中的比重计。更具体地说，它还没有与圆柱形磁流变仪一起使用（如桩或CPT）。相反，一个“平面应变”的理想化已被使用，这有效地假设，在一个水平方向的范围是无限的，该建议的主要重点是开发一个（半）圆柱形的应变仪和土壤物理模型，这将允许相关的土壤运动进行观察。这项技术将用于土工离心机，利用数字摄影技术跟踪土壤的运动。结果将提供基本的比较与“平面应变”的理想化，这是目前用来观察土壤运动，和（全）圆柱形应变计，它不允许土壤运动被视为。实际上，该技术在岩土工程轴对称（圆形）物理模型的所有领域都有潜在的应用，使用离心模型意味着结果将适用于全尺寸情况（如打入桩）。然后，该技术将被用来观察阻力渗透与土壤运动的同时，适用于局部方面的行为，如“规模效应”的探头，一个“分层”土壤剖面的影响，和粗糙度的探头轴。

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.