Screw piles for wind energy foundation systems

螺旋（或螺旋）桩是拧入地面的基础。由于具有良好的抗拉和抗压性能，它们被广泛用于陆上支撑高速公路标志和门架。该项目旨在使螺旋桩成为海上风力发电场更有吸引力的基础（或锚固）选择，这些风力发电场被部署在更深的水域，并且受到越来越多的性能需求的影响。英国在可再生能源领域的扩张目标颇具挑战性，到2020年可能会有5000多台海上风力涡轮机。向更深的水域移动将增加成本，并对海底结构和基础提出更高的要求。目前正在考虑的这些应用的基础解决方案是灌注桩，大型单桩或混凝土重力基础结构（GBS）。在近海大量打桩引起了对植物可用性和对海洋哺乳动物影响的担忧。也有人担心实际单桩发展的限制和GBS的高材料需求。螺旋桩有潜力克服这些问题，并且可以在现有陆上系统的基础上进行扩展，这些系统的安装噪音相对较低，在抗拉和抗压能力方面都很高效。为了满足海上需求，螺旋桩将需要增强几何形状，但预计最初这些将是适度的，以便将陆上技术转移到海上。这将导致部署几个较小的桩或桩群，而不是直接移动到非常大的单螺旋桩，这可能证明难以安装和需要大量投资。为了将螺旋桩作为海上风电的基础解决方案，该项目将开发具有优化几何形状的桩，以最大限度地减少安装阻力，但能够承受高横向和力矩载荷。为了安装螺旋桩，采用扭矩装置将锚杆有效地旋入地面。随着桩尺寸要求的增加和几何形状的潜在变化，该项目将开发改进的，较少经验的技术来预测各种土壤条件下所需的扭矩。这将使人们对桩的安装有信心，并对适当规模的安装工厂进行投资。随着新的桩几何形状的开发，需要对它们进行测试（通过模型、数值和现场测试），以验证它们能够满足海上环境的性能要求。该项目还将开发定制分析技术，为岩土工程师提供设计地基所需的工具，为承包商提供安装过程所需的工具。由于桩可以作为大型单个单元或较小的单元组合部署，因此将探讨组合部署和多种基础几何形状的效率，因为使用几个较小几何形状的基础可以降低海上安装期间的风险，并且由于制造成本和对安装设备的要求较低，实际上更经济。将上述调查领域结合起来，形成一个设计和决策工具包，供岩土设计人员使用，以便以高效和经济的方式部署螺旋桩作为海上基础。这项研究有可能使海上可再生能源更容易部署螺旋桩基础。该项目将开发能够处理当前水深的基础，并将提供随着水深和对基础的需求增加而对桩的行为的理解。通过利用螺旋桩/锚技术的安装和性能优势，该项目的成果将有助于降低可再生能源发电的整体成本，并增加公众对这种能源未来可行性的信心。

Screw (or helical) piles are foundations which are screwed into the ground. They are widely used onshore for supporting motorway signs and gantries as they possess good tensile and compressive resistance. This project aims to make screw piles a more attractive foundation (or anchoring) option offshore for wind farms, which are being deployed in deeper water and subject to increasing performance demands. The UK has challenging targets for expansion of energy from renewables with the potential for over 5000 offshore wind turbines by 2020. The necessary move to deeper water will increase cost and put greater demands on subsea structures and foundations. The current foundation solutions being considered for these applications are driven piles, large monopiles or concrete gravity based structures (GBS). Driving of piles in large numbers offshore causes concerns over plant availability and impact on marine mammals. There are also concerns over the limit of practical monopile development and the high material demands of GBS. Screw piles have the potential to overcome these issues and are scalable for future development from current onshore systems which have relatively low noise installation and are efficient in terms of both tensile and compressive capacity. To meet offshore demands, screw piles will require geometry enhancement but it is envisaged that these will initially be modest to allow de-risked transfer of onshore technology offshore. This will lead to the deployment of several smaller piles or pile groups rather than moving straight to very large single screw piles that may prove difficult to install and require significant investment. To allow screw piles to be considered as a foundation solution for offshore wind this project will develop piles with optimised geometries that minimise resistance to installation but are capable of carrying high lateral and moment loads. In order to install screw piles torque devices are used to effectively screw the anchors into the ground. With increased pile size requirements and potential changes in geometry this project will develop improved, less empirical techniques to predict the torque required in a variety of soil conditions. This will allow confidence in pile installation and investment in appropriately sized installation plant. As new pile geometries are being developed these will need to be tested (through model, numerical and field testing in this project) to verify that they can meet the performance demands of the offshore environment. The project will also develop bespoke analysis techniques to allow consulting geotechnical engineers the tools they require to design the foundations and contractors the tools to inform the installation processes. As piles can be deployed as large single units or smaller units in groups the efficiency of group deployment and multiple foundation geometries will be explored, as using several smaller geometry foundations could reduce the risks during offshore installation and actually be more economic due to lower fabrication costs and demands on installation plant. The areas of investigation above will be combined to produce a design and decision making toolkit for use by geotechnical designers to allow deployment of screw piles as offshore foundations in an efficient and cost effective manner.The research has the potential to make it easier to deploy screw pile foundations for offshore renewables. This project will develop foundations able to deal with current water depths and will provide understanding of the behaviour of piles as water depths and the demands on the foundations increase. By harnessing the installation and performance benefits of screw pile/anchor technology, the results of the project will contribute to an overall cost reduction in electricity generated by renewable means and increase the public's confidence in the future viability of this energy source.