工程土质边坡是铁路、公路和防洪基础设施的主要组成部分。它们对于关键服务的安全、可靠和经济运行至关重要。
但是，这些资产的故障很常见。越来越多的证据表明，老化的基础设施、密集使用和气候变化导致的极端环境有可能增加故障的规模和频率。
2020 年 8 月在阿伯丁郡斯通黑文发生的致命事故使这些风险成为人们关注的焦点。由于强降雨引发冲刷山体滑坡，火车脱轨导致三人死亡。随后的两次独立审查就英国铁路网络更好地应对极端天气的方式提出了 50 多条建议。
对天气和气候变化对土方资产影响的了解不足是开发和维护弹性基础设施的重大障碍。
当前的设计和资产管理方法使这种情况长期存在，因为它们基于历史经验，不能总是推断以预测未来的性能。
长寿命、长线性资产 (Achilles)
应对这些挑战需要了解英国遇到的各种地质材料的土方边坡破坏的多种机制，包括相关的恶化过程和触发事件。
作为英国研究工作的一部分，长寿命、长线性资产 (Achilles)计划拨款的评估、成本核算和增强侧重于了解粘土切割和路堤土方工程斜坡中天气驱动的恶化过程，这些过程可能导致浅层破坏（图1 ).
由英国工程与物理科学研究委员会资助，Achilles 于 2018 年 7 月开始。
这是纽卡斯尔大学、拉夫堡大学、达勒姆大学、南安普顿大学、巴斯大学和利兹大学研究部门之间为期四年半的合作；英国地质调查局；和项目合作伙伴，包括环境署、国家公路、网络铁路、莫特麦克唐纳和雅各布斯。
正在解决的一个关键问题是：为什么粘土土方边坡在过去多次经历过类似天气事件的情况下会在长时间的潮湿天气中倒塌？
推论是随着时间的推移，退化过程会降低土壤的可用强度。面临的挑战是将研究和技术的进步与行业主导的设计和资产管理实践创新结合起来，以减少基础设施系统因退化和未来变化而面临的风险。
Achilles 的目标是开发评估、监测、设计和修复由细粒土壤建造的路堤和岩屑岩土工程性能所需的工具，通过推进三个研究挑战的知识：恶化过程；资产绩效；以及预测和决策支持（图 2）。
这是通过三个方面的工作来实现的：表征材料；资产规模流程分析；和评估网络规模的性能。
还有一个重点是四个主题：
- 性能和恶化——将对通过研究开发的概念和过程的理解与利益相关者的观察和经验联系起来
- 监控和测量——从实验室和资产规模的观察中学习，以提供知识库来理解过程，从而导致模型开发和验证
- 模拟和建模——采用长时间的天气序列（例如长达 200 年的每日天气）作为捕获恶化过程的数值模型的输入，包括使用气候情景来探索未来可能的趋势，并建立升级到网络规模的方法
- 决策和设计——评估数据的价值并提供工具以实现更好的设计和决策。
Achilles 的一个关键组成部分是对示例性粘土土方工程斜坡进行长期野外观测记录的制作和使用。
其中包括： 纽伯里高塑性伦敦粘土的公路切坡，具有 18 年的监测数据；泰恩河畔纽卡斯尔附近中等塑性粘土 Bionics 的全尺寸铁路/公路路堤，有 15 年的数据；以及由 Achilles 财团发起的低塑性粘土防洪堤观测站。
天气、孔隙水压力、水分含量和变形的测量——加上现场和实验室测量——被用来量化流体力学过程之间的相互作用，并验证退化的数值模型。
许多研究都试图开发数值模型来研究天气驱动的恶化过程，但很少有研究能够获得如此丰富和广泛的现场数据来促进严格的验证。
长寿命、长线性资产 (Achilles)迄今为止的重要成果包括：
- 基于实验室和现场测量的干湿循环下粘土退化的概念模型
- 包含退化的粘土本构模型
- 一个经过验证的数值模型，可以复制在粘土边坡中观察到的季节性（润湿和干燥）棘轮变形行为
- 粘土边坡的天气驱动的资产恶化曲线，包括未来的气候情景
- 对伦敦至布里斯托尔铁路线的失效建模时间与观察到的边坡失效记录进行有利比较
- 深入了解土钉等工程干预措施的好处和最佳时机，以延长斜坡寿命
- 开发统计仿真器以促进快速生成退化曲线，从而评估一系列几何形状和土壤参数的边坡设计寿命
- 为资产提供目标设计寿命的参数选择建议。
工程斜坡模拟器
尽管 Achilles 计划取得了许多成功和好处，但一个持续的挑战是从已经恶化到失效的粘土土方边坡获得测量值。这需要确认渐进的斜坡变形行为与天气序列的反应之间的联系——例如干旱和长时间潮湿天气的周期。
这种需求导致了在拉夫堡大学建造和运营大型工程粘土边坡模拟器设施的提议。
已从 Wolfson 慈善基金会收到 500,000 英镑的赠款，用于交付该设施，并将作为 Achilles 的一部分进行首次斜坡模拟。
工程边坡模拟器是一个可配置的气候控制测试设施，用于研究粘土路堤边坡中天气驱动的浅层过程。使用一系列常见问题的粘土，将在专门设计的建筑物内的倾斜台上建造斜坡。在那里，它们将经受模拟季节性天气条件和极端环境事件的受控润湿和干燥的加速循环。
工作台将倾斜并保持在土方坡度的典型角度，同时承受循环。
通过安装在土壤斜坡上的大量仪器进行持续监测，将提供有关不同天气模式和极端事件对耦合水力机械过程影响的独特信息。
模拟完成后，斜坡将倾斜 45° 以导致失效，从而提供剩余强度能力的度量。
无法通过现场试验获得此信息，因为要使现有斜坡失效在技术上很困难且成本很高。倾斜台还将用于调查斜坡工程干预的性能，直至并包括故障，以优化斜坡修复和设计策略。
倾斜台本质上是一个钢箱，在箱内建造一个大型的夯实土边坡（图3）。
斜坡长 5 米，宽 3 米，土壤厚度为 1.5 米，以模拟斜坡上的表层土壤层。
重约 45 吨的土壤自重将复制现场所经历的影响边坡退化和不稳定的力。
形成斜坡的土壤的材料特性，例如压实层的密度和稠度，将使用现场规模的压实工艺和设备进行再现，由于工作台的尺寸较大，因此可以实现这一点。
在模拟的无限斜坡条件下的渐进式破坏是通过使用主动趾来促进的。这是通过在斜坡脚趾处使用一块板来支撑土体来实现的。
如果土壤强度退化并且斜坡向下移动，则板上增加的压力将启动千斤顶将趾板从土壤中移开以保持恒定的支撑条件。
这将允许在发展中的剪切带调动峰值后的土壤强度，从而可能导致边坡失稳。
预计测试将于 2022 年秋季开始，每次实验需要 6 到 12 个月。
由 Achilles 提供并使用工程斜坡模拟器设施扩展的研究计划将研究和技术的新进展与行业领先的设计和管理实践进步结合在一起，适用于一系列粘土土方资产类型。
目的是减少因恶化和未来变化而对基础设施系统构成的风险。研究成果将告知利益相关者及时承诺资源以应对这些风险。
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Landslides: Understanding and simulating failures
25 JANUARY, 2022BY GEEDITORIAL
Loughborough University geotechnical engineering professor Neil Dixon and civil engineering senior lecturer Alister Smith on clay earthwork slope failures and current research into weather driven deterioration.
Engineered soil slopes are major components of rail, road and flood defence infrastructure. They are vital to the safe, reliable and economic operation of critical services.
However, failure of these assets is common. There is growing evidence that ageing infrastructure, intensive use and environmental extremes caused by climate change threaten to increase the scale and frequency of failures.
These risks were brought into focus by the fatal accident at Stonehaven, Aberdeenshire, in August 2020. Three people were killed following derailment of a train when a washout landslide was triggered by intensive rainfall. Two subsequent independent reviews have made more than 50 recommendations about ways the UK’s rail network can better cope with extreme weather.
A poor understanding of weather and climate change impacts on earthwork assets is a significant barrier to the development and maintenance of resilient infrastructure.
Current approaches to design and asset management perpetuate this situation because they are based on historical experience, which cannot always be extrapolated to predict future performance.
It is therefore vital to understand and anticipate when and why earthwork failures might occur to enhance preventative action and build more resilient structures in the future.
Achilles
Addressing these challenges requires knowledge of the multiple mechanisms of earthwork slope failures for the range of geological materials encountered in the UK, including associated deterioration processes and trigger events.
As part of the UK research effort, the Assessment, Costing and Enhancement of Long Life, Long Linear Assets (Achilles) programme grant is focused on understanding weather-driven deterioration processes in clay cutting and embankment earthwork slopes that can result in shallow failures (Figure 1).
Funded by the UK Engineering & Physical Sciences Research Council, Achilles commenced in July 2018.
It is a four and a half year collaboration between research departments at Newcastle, Loughborough, Durham, Southampton, Bath and Leeds universities; the British Geological Survey; and project partners, including the Environment Agency, National Highways, Network Rail, Mott MacDonald and Jacobs.
A key question being addressed is: why can clay earthwork slopes fail during a prolonged period of wet weather when they have survived similar weather events many times in their past?
The inference is that over time, deterioration processes reduce available strength of the soil. The challenge is to bring together advances in research and technology with industry-led innovation in design and asset management practice to reduce the risks posed to infrastructure systems from deterioration and future change.
Achilles aims to develop the tools necessary to assess, monitor, design and repair the geotechnical performance of embankments and cuttings constructed from fine grained soils through advancing knowledge in three research challenges: deterioration processes; asset performance; and forecasting and decision support (Figure 2).
This is being achieved by working across three scales: characterising the materials; analysis of asset-scale processes; and assessment of network-scale performance.
There is also a focus on four themes:
Performance and deterioration – linking understanding of concepts and processes developed via research with stakeholder observations and experience
Monitoring and measurement – learning from laboratory and asset-scale observations to deliver the knowledge base to understand processes, leading to model development and validation
Simulation and modelling – employing long weather sequences (for example up to 200 years of daily weather) as input to numerical models capturing deterioration processes, including use of climate scenarios to explore possible future trends, and establishing approaches for upscaling to network scale
Decisions and design – evaluating the value of data and delivering tools for better design and decision making.
A critical component of Achilles is the production and use of long field observational records for exemplar clay earthwork slopes.
These comprise: a highway cut slope in high-plasticity London Clay in Newbury with 18 years of monitoring data; the full-scale rail/road embankment at Bionics in intermediate-plasticity clay near Newcastle upon Tyne with 15 years of data; and a low-plasticity clay flood embankment observatory initiated by the Achilles consortium.
Measurements of weather, pore water pressures, moisture content and deformations – coupled with field and laboratory measurements – are being used to quantify the interaction between hydro-mechanical processes and to validate numerical models of deterioration.
Many studies have attempted to develop numerical models to investigate weather-driven deterioration processes, but few, if any, have had access to such rich and extensive field data to facilitate rigorous validation.
Important outputs from Achilles to date include:
A conceptual model for deterioration of clay soils subject to cycles of wetting and drying based on laboratory and field measurements
A clay constitutive model incorporating deterioration
A validated numerical model that can replicate observed seasonal (wetting and drying) ratcheting deformation behaviour in clay slopes
Weather-driven asset deterioration curves for clay cut slopes, including future climate scenarios
Favourable comparison of modelled times to failure with observed slope failure records for the London to Bristol rail line
Insight into the benefits and optimum timing of engineering interventions such as soil nails to extend slope life
Development of a statistical emulator to facilitate rapid production of deterioration curves and hence assessment of slope design life for a range of geometries and soil parameters
Recommendations for parameter selection to deliver targeted design life for an asset.
Engineered slope simulator
Despite the many successes and benefits of the Achilles programme, a continuing challenge is obtaining measurements from a clay earthwork slope that has deteriorated towards failure. This is required to confirm the link between progressive slope deformation behaviour in response to weather sequences – for example cycles of dry and prolonged periods of wet weather.
This need led to a proposal to build and operate a large scale engineered clay slope simulator facility at Loughborough University.
A grant of £500,000 has been received from the Wolfson Foundation charity to deliver the facility, with the first slope simulations to be undertaken as part of Achilles.
The Engineered Slope Simulator is a configurable climate-controlled testing facility for investigating weather-driven shallow processes in clay embankment slopes. Using a range of common problem clay soils, slopes will be constructed on a tilting table housed in a purpose designed building. There, they will be subjected to accelerated cycles of controlled wetting and drying that simulate seasonal weather conditions and extreme environmental events.
The table will be tilted and held at an angle typical of an earthwork slope while subjected to the cycles.
Continuous monitoring via extensive instrumentation installed in the soil slope will provide unique information about the impact of different weather patterns and extremes on coupled hydro-mechanical processes.
On completion of the simulation, the slope will be tilted up to 45° to cause failure, providing a measure of the remaining strength capacity.
This information cannot be obtained via field trials as it is technically difficult and costly to bring an existing slope to failure. The tilting table will also be used to investigate the performance of slope engineering interventions, up to and including failure, to allow optimisation of slope repair and design strategies.
The tilting table is in essence a steel box in which a large-scale compacted soil slope will be constructed (Figure 3).
The slope will measure 5m long by 3m wide with a soil thickness of 1.5m to simulate the surface soil layer on a slope.
Weighing in the order of 45t, the soil self-weight will replicate forces experienced in the field that influence slope deterioration and instability.
Material properties of the soil forming the slope such as density and consistency of compacted layers will be reproduced using field-scale compaction processes and equipment, which is achievable due to the large size of the table.
Progressive failure under simulated infinite slope conditions is facilitated by using an active toe. This is achieved using a plate at the toe of the slope to support the soil body.
If deterioration of the soil strength occurs and the slope moves downslope, increased pressure on the plate will activate jacks to move the toe plate away from the soil to maintain constant support conditions.
This will allow mobilisation of post peak soil strengths in developing shear zones, potentially leading to slope failure.
Testing is expected to commence in autumn 2022, with each experiment taking between six and 12 months.
The programme of research being delivered by Achilles and extended using the Engineered Slope Simulator facility is bringing together new advances in research and technology, with industry-led advances in design and management practices, for a range of clay earthwork asset types.
The aim is to reduce the risks posed to infrastructure systems from deterioration and future change. The research outcomes will inform timely commitment of resources by stakeholders to address these risks.
Thurlby R (2013) Managing the asset time bomb: a system dynamics approach. Proceedings of the Institution of Civil Engineers-Forensic Engineering, 166(3), 134-142.