Co-UDlabs_WP7_development of mechanistic models to simulate deterioration of drainage assets

Sewer and stormwater drainage networks consist of mainly buried jointed pipes. These networks are large and complex and contain a range of underground assets. These assets are expected to operate for many decades and are subjected to a range of forces, which are influenced firstly by internal factors such as water flows and pressures, and secondly by external factors such as local soil and traffic loading conditions. There have been a small number of academic studies that have aimed to investigate how in-pipe defects develop but these have often been hindered by scale or instrumentation issues. Some lack complexity and scale, and simulate the pipe defect in a simplistic manner, e.g. the small-scale experiments of Guo et al., (2013), and Tang et al. (2022) studied the impact of pipe exfiltration on the erosion of surrounding soil, and others have used small scale pipes with poorly described defects for example Khan and Patil (2018) in their testing on measuring in-pipe cracks. Typically, academic studies use small scale surrogates that lack the complexity of the full-scale system. It was an objective of this work that full-scale surrogates would be used to better understand the mechanisms behind deterioration. In trying to achieve this objective we appreciated not only the difficulty in measuring defect development but also the wide range of possible defects that could be studied. The team examined the data on defect type likelihood in order to select a relevant defect in terms of likelihood. Berger et al., (2020) indicated that the third most common defect in sewer and drainage systems was defective pipe connections and joints. Studies in the UK have estimated that 40-50% of the flow entering wastewater treatment works (WWTW) in at least 25% of the sewer catchments in the UK is from unintended infiltration via leaky joints (UKWIR, 2012). Indirect evidence of large-scale infiltration is strong with many WWTPs treating unexpectedly larger daily flow volumes with the subsequent higher energy use and carbon emissions. This “extra” flow results both in unnecessary wastewater treatment and in the worst-case scenario localised flooding and extra overflow spills due to system capacity exceedance during extreme weather events. This indicated that defective pipe joints/connections can have a significant impact on the performance of many sewer and drainage systems. The physical resilience of shallow, buried pipe systems is ultimately governed by the geotechnical properties of the fill surrounding the pipes. Sewer and drainage pipes are susceptible to joint articulation and deformations because they are generally only partially full and thus buoyant relative to surrounding water-filled backfill. Such pipes are mostly buried in the vicinity of the ground water table, the surrounding soil is partially saturated. Often these pipes are buried close to the ground surface so suffer from surface loading such as from traffic. Elshesheny et al., (2019) observed that pipes buried deeper experienced lower stresses and less deformation than pipes installed closer to the ground surface. Wu et al., (2020) indicated that pipes buried at a depth of less than 5 pipe diameters are particularly susceptible to dynamic loading. This is the range of depths that many sewer and drainage pipes are buried. Small scale testing by Ratkitin and Xu, (2015) indicated that applied traffic loads to concrete pipes could have an impact on vertical displacement and rotation. So, although the geotechnical community has investigated the potential for joint displacement and movement, these studies have never examined the potential infiltration/exfiltration from a displaced joint. Therefore, researchers at USFD and IKT decided to investigate the levels of infiltration/exfiltration possible from displaced joints (measured at full-scale) and if the level of joint displacement would be replicated in a buried pipe under realistic loading. As the investigation progressed, an instrumentation need was identified, that is the need to be able to measure the actual internal displacement and rotation within a joint that had been loaded so that the tests at both IKT and USFD could be compared. A second requirement was added to the investigation and that was to develop a measurement method to measure the movement of internal pipe joints so that we could investigate what type and level joint movement could be linked to infiltration/exfiltration rates. By gaining such information for typical sewer pipes, it was intended to elucidate the mechanisms that may be the cause of joint displacement and subsequent exfiltration/infiltration in shallowly buried sewer and drainage pipes. S EN 1610 (2015). Construction and testing of drains and sewers. British Standards Institution., London. Berger, C.; et al. (2020). Zustand der Kanalisation in Deutschland. Ergebnisse der DWA-Umfrage 2020. Sonderdruck aus KA Korrespondenz Abwasser, Abfall. 67. Jahrgang. Heft 12/2020, S. 939-953. https://de.dwa.de/files/_media/content/03_THEMEN/Entwaesserungssysteme/Kanalumfrage/Zustand-der-Kanalisation-2020.pdf (accessed 13/04/2023). In German.DIN 1986-30:2012-02. Entwässerungsanlagen für Gebäude und Grundstücke - Teil 30: Instandhaltung (drainage systems on private ground - Part 30: Maintenance). DIN – Deutsches Institut für Normung. DIN Media GmbH, Berlin. DIN EN 476:2022-09. Allgemeine Anforderungen an Bauteile für Abwasserleitungen und -kanäle; Deutsche Fassung EN 476:2022 (General requirements for components used in drains and sewers; German version EN 476:2022). DIN – Deutsches Institut für Normung. DIN Media GmbH, Berlin.Guo S., Shao Y., Zhu D., Zhang Y. (2013) Physical modelling on sand erosion around defective sewer pipes under the influence of groundwater. Journal of Hydraulic Engineering 139(12) 1247-1257.Khan M.S., Patil R., (2018) Acoustic Characterization of PVC Sewer Pipes for Crack Detection Using Frequency Domain Analysis, 2018 IEEE International Smart Cities Conference (ISC2), Kansas City, MO, USA, 2018, pp. 1-5, doi: 10.1109/ISC2.2018.8656739.Rakitin B., Xu M. (2015) Centrifuge testing to simulate buried reinforced concrete pipe joints subjected to traffic loading. Can. Geotech. Journal, 52, 1762-1774. https://cdnsciencepub.com/doi/pdf/10.1139/cgj-2014-0483Tang Y., Zhu D.Z., Chan D.H., Zhang S. (2022) Physical and analytical modelling of soil loss caused by a defective sewer pipe with different defect locations. Acta Geotechnica, doi:10.1007/s11440-022-01747-7.UKWIR (2012), Economics of Infiltration Reduction, Report Ref. No. 15/SW/01/11, UK Water Industry Research.Wu J., Kouretzis G., Suwal L., Ansari Y., Sloan S.W. (2020) Shallow and deep failure mechanisms during uplift and lateral dragging of buried pipes in sand. can. Geotechnical Journal, 57, 1472-1483. https://cdnsciencepub.com/doi/pdf/10.1139/cgj-2019-0281.市政污水与雨水排水管网主要由埋地式节段管道组成。此类管网规模庞大且结构复杂，涵盖多类地下设施资产。这些设施的设计服役年限可达数十年，且承受多种作用力：一方面受管内水流、水压等内部因素影响，另一方面受当地土壤条件、交通荷载等外部因素制约。 目前已有少量学术研究致力于探究管内缺陷的演化机制，但此类研究常受限于试验尺度或仪器监测问题。部分研究缺乏足够的复杂度与试验尺度，仅以简化方式模拟管道缺陷：例如Guo等人（2013）与Tang等人（2022）开展的小尺度试验，仅研究了管道渗逸（exfiltration）对周边土壤侵蚀的影响；另有部分研究采用缺陷描述模糊的小尺度管道开展试验，如Khan与Patil（2018）在管内裂纹检测试验中所使用的试件。总体而言，现有学术研究多采用小尺度替代试件，无法复现全尺寸系统的复杂工况。本研究的核心目标之一，便是采用全尺寸替代试件，以更深入地解析管道劣化的内在机制。为达成该目标，研究团队意识到不仅缺陷演化的监测存在较大难度，同时可研究的管道缺陷类型也较为多样。研究团队通过分析缺陷类型的发生概率数据，筛选出具有较高工程相关性的缺陷类型。Berger等人（2020）的研究表明，污水与排水系统中第三大常见缺陷为管道接口（joint）与连接部位失效。 英国相关研究估算，英国至少25%的污水汇水区中，进入污水处理厂（wastewater treatment works, WWTW）的水流有40%-50%来自管道接口泄漏导致的非计划性入渗（infiltration）（UKWIR，2012）。诸多污水处理厂实际处理的日处理水量远超预期，随之带来能耗与碳排放的额外增加，这为大规模入渗问题提供了强有力的间接证据。这类“额外”水流不仅造成不必要的污水处理能耗，在极端天气工况下，还可能因系统处理容量超限，引发局部内涝与额外的溢流排污事件。由此可见，管道接口/连接部位失效会对大量污水与排水系统的运行性能造成显著负面影响。 浅埋式埋地管道系统的结构力学性能，最终由管道周围回填土的岩土工程特性决定。由于管道通常仅部分充水，相较于周围充满水的回填土，管道会受到浮力作用，因此极易发生接口铰接与变形。此类管道多埋设于地下水位附近区域，周边土壤处于部分饱和状态。且不少管道埋深较浅，易承受地面荷载（如交通荷载）作用。Elshesheny等人（2019）的研究发现，相较于埋深较浅的管道，埋深更大的管道所受应力更低、变形更小。Wu等人（2020）指出，埋深小于5倍管道直径的管道，对动态荷载尤为敏感。多数市政污水与排水管道的埋深正处于该区间内。Ratkitin与Xu（2015）开展的小尺度试验表明，作用在混凝土管道上的交通荷载会对管道的竖向位移与转角产生影响。因此，尽管岩土工程领域已针对管道接口位移与活动开展了相关研究，但此类研究从未探讨过接口位移后可能产生的渗逸/入渗问题。 因此，USFD与IKT的研究人员决定开展相关试验，以探究接口位移后可能产生的渗逸/入渗水平（采用全尺寸试件测试），并验证在实际荷载作用下，埋地管道的接口位移是否可复现该渗滤水平。随着研究推进，团队发现亟需一套监测方案：能够实时测量受载接口内部的实际位移与转角，以便对USFD与IKT两地的试验结果进行比对。随后，研究又新增了第二项目标：开发一套管道内部接口位移的监测方法，以探究何种类型与程度的接口位移会与渗逸/入渗速率相关联。 通过获取典型市政污水管道的相关试验数据，本研究旨在阐明浅埋式污水与排水管道的接口位移机制，以及由此引发的渗逸/入渗过程。 S EN 1610（2015）. 排水管道工程施工与测试. 英国标准协会，伦敦。 Berger, C.; 等.（2020）. 德国下水道系统现状：2020年DWA调查结果. 载于《废水、废弃物通讯》（KA Korrespondenz Abwasser, Abfall）第67卷2020年第12期，第939-953页. https://de.dwa.de/files/_media/content/03_THEMEN/Entwaesserungssysteme/Kanalumfrage/Zustand-der-Kanalisation-2020.pdf（2023年4月13日访问）. 德文版。 DIN 1986-30:2012-02. 建筑与地块排水系统——第30部分：维护（私人场地排水系统第30部分：维护）. 德国标准化学会，DIN Media GmbH，柏林。 DIN EN 476:2022-09. 排水管道与下水道用组件通用要求；德文版EN 476:2022. 德国标准化学会，DIN Media GmbH，柏林。 Guo S., Shao Y., Zhu D., Zhang Y.（2013）. 地下水作用下破损市政管道周边砂土侵蚀的物理模拟. 《水利工程学报》，139(12)：1247-1257。 Khan M.S., Patil R.（2018）. 基于频域分析的PVC市政管道裂纹检测声学特性研究. 2018 IEEE国际智能城市会议（ISC2），美国密苏里州堪萨斯城，2018年，第1-5页. doi: 10.1109/ISC2.2018.8656739。 Rakitin B., Xu M.（2015）. 模拟交通荷载作用下埋地钢筋混凝土管道接口的离心机试验. 《加拿大岩土工程学报》，52：1762-1774. https://cdnsciencepub.com/doi/pdf/10.1139/cgj-2014-0483。 Tang Y., Zhu D.Z., Chan D.H., Zhang S.（2022）. 不同缺陷位置的破损市政管道引发土壤流失的物理与分析模型. 《岩土力学学报》，doi:10.1007/s11440-022-01747-7。 UKWIR（2012）. 入渗削减经济效益，报告编号15/SW/01/11，英国水务行业研究协会。 Wu J., Kouretzis G., Suwal L., Ansari Y., Sloan S.W.（2020）. 砂土中埋地管道上浮与侧向拖拽过程中的浅埋与深埋失效机制. 《加拿大岩土工程学报》，57：1472-1483. https://cdnsciencepub.com/doi/pdf/10.1139/cgj-2019-0281。