DOI: 10.5281/zenodo.15276534
title: Co-UDlabs_WP7_development of mechanistic models to simulate deterioration of drainage assets

description: 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.