Offshore Cable Burial: How deep is deep enough?

海上风电（OSW）对英国的经济和能源安全至关重要。这也是一个巨大的投资领域，例如，到2021年底，140亿英镑已承诺用于新的OSW站点，这是英国第四大建设项目。除此之外，英国目前的2030年OSW装机容量目标将需要480亿英镑的投资，并为2.7万人提供直接就业机会。尽管OSW行业日益成熟，但已安装的基础设施的某些元素仍然存在问题。目前，与海底电力电缆相关的问题占所有保险索赔费用的75%，而海底电力电缆是将海上风力发电机产生的电力传输到陆上输电系统的管道，故障通常需要100天以上的时间才能修复。这将导致供应中断和风力发电场运营商的收入损失，从长远来看，这可能导致更长的投资回收期，并减少其可再生能源投资组合中的其他投资。在浅水中，必须保护这些电缆不受锚和渔具的影响，主要的保护方法是将电缆埋在海底以下。电缆的埋深是经济成本（更深需要更长的时间，需要更大的船只，可能需要更复杂的操作）和电缆被锚/渔具穿透海床损坏的风险之间的折衷。在这种情况下，锚索相互作用目前占电力电缆故障的85%。英国海上风电的快速扩张计划——未来30年装机容量将增加7.5倍——将需要在世界上一些最繁忙的航运/捕鱼水域安装新的电缆，这些新电缆安装在适当的深度是至关重要的。然而，目前行业缺乏适当的科学工具来确定不同土壤条件下锚杆的穿透深度。相反，他们使用简单的查找表，该表基于海底土壤的非常广泛的描述性分类，基本上将大量的真实土壤条件分为两类——软土壤和硬土壤。这种方法已被证明在一些土壤中是高度保守的，导致不必要的深埋（和昂贵的）。然而，在其他条件下，它显然是非保守的，因为锚索与锚索的相互作用主导了锚索的失效。该提案将解决缺乏可靠的锚贯入模型的问题，并通过物理测试和计算建模，开发一个工具包来评估不同土壤条件下锚贯入的情况。该锚穿深预测工具将基于电缆路线沿线的现场调查数据，避免使用过于简单的查找表。它的发展将由一个工业项目指导小组指导，该小组由OSW部门的主要各方组成。至关重要的是，这种创新的锚贯模型将使用包含实际现场调查数据的地理数据库进行校准和验证。模型的性能将根据已证实的、可论证的地面条件进行评估，因此不会依赖于假设的地面条件，因为假设的地面条件可以使用当前的电缆掩埋评估技术进行过度简化（例如，与更复杂的多层土壤类型相反，描述的单一类型土壤不随埋深变化）。除了锚贯贯预测工具外，还将创建许多空间测绘层（特定于英国大陆架），这些层来自于该工具在英国海底已知地面条件下的应用。这些绘图层将公开提供，并预计将在项目概念阶段提供给高层空间规划决策。总之，该项目将提供一个行业可用的锚贯模型，使OSW部门能够回答关键的电缆埋深问题——多深才够深？

Offshore Wind (OSW) is critical for the UK's economy and energy security. It is also an area of huge investment, for example £14bn has been committed up to the end of 2021 for new OSW sites - the 4th largest construction programme in the UK. Beyond this, the UK's current 2030 OSW installed capacity targets will require £48bn of investment and provide direct employment for 27,000 people.Despite the growing maturity of the OSW sector, certain elements of the installed infrastructure remain problematic. Principally, problems associated with subsea power cables that transport and distribute the electricity generated offshore in wind turbine generators to the onshore transmission system currently account for 75% of the cost of all insurance claims and faults typically take 100+ days to rectify. This leads to breaks in supply and loss of revenue for the wind farm operator which in the long term can lead to longer payback periods and reduced investment elsewhere in their renewables portfolio. In shallow waters these cables must be protected from anchors and fishing gear and the primary protection method is to bury the cable below the seabed. The cable burial depth is a compromise between economic cost of burial (going deeper takes longer, requires larger ships and may require more complex operations) and risk to the cable being damaged by anchors/fishing gear penetrating the seabed. Within this context, anchor-cable interactions currently account for 85% of power cable failures. The planned rapid expansion of offshore wind around the UK - installed capacity increasing 7.5 times over the next 30 years - will require new cable installations within some of the busiest shipping/fishing waters in the world and it is essential that these new cables are installed at the appropriate depth. However, the industry currently lacks appropriate scientific tools to determine anchor penetration depths in different soil conditions. Instead they use simple look-up tables based on very broad descriptive classifications of the soils on the seabed that basically split the huge spectrum of real soil conditions into two categories - soft or hard. This approach has been shown to be highly conservative in some soils leading to unnecessarily deep (and costly) burial. However, it is clearly non-conservative in other conditions as anchor-cable interactions dominate cable failures. This proposal will tackle the lack of sound anchor penetration models head on and, through physical testing and computational modelling, develop a toolkit to assess anchor penetration in different soil conditions. This anchor penetration prediction tool will be based on the site investigation data typically available along cabling routes and avoid the use of oversimplistic look-up tables. Its development will be guided by an industrial project steering group made up of key parties from the OSW sector. Crucially, this innovative anchor penetration model will be calibrated and validated using a geodatabase comprising actual site investigation data. Model performance will be assessed against proven, demonstrable ground conditions and therefore will not rely on hypothetical ground conditions which can be oversimplified using current cable burial assessment techniques (e.g. descriptive single-type soils that do not change with burial depths, as opposed to more complex, multi-layered soil types). In addition to the anchor penetration predictive tool, a number of spatial mapping layers (specific to the UK Continental Shelf) will be created, derived from the tool application to known ground conditions across the UK seafloor. These mapping layers will be made openly available, and are anticipated to feed into high-level spatial planning decisions at project concept stage.In summary, this project will provide an industry usable anchor penetration model allowing the OSW sector to answer the key cable burial question - how deep is deep enough?