Distributed Fibre-optic Cable Sensing for Buried Pipe Infrastructure

Lead Research Organisation: University of Sheffield
Department Name: Mechanical Engineering

Abstract

In the UK the 600,000 km long underground sewer system (including private sewers) is ageing and poorly monitored. In continental Europe, the total value of the sewer assets amounts to 2 trillion Euros. The US EPA estimates that sewer collection systems in the USA have a total replacement value between $1 and $2 trillion. In China alone 40,000 km of new sewer pipes are laid every year. The system is subject to increasing capacity demands because of increased urbanisation and climate change. OFWAT (UK) and similar regulatory bodies in the developed countries impose a legal duty on water utilities to maintain the conditions of their sewer systems and to reduce the risk of flooding incidents. Consequently, monitoring pipes for obstructions and defects remediation forms an important part of an effective management programme to reduce sewer flooding and optimise the operational and maintenance costs. Existing sewer survey methods are limited to the interpretation of CCTV and LightLine images which are relatively slow and require a mobile trolley with camera to traverse through individual sewer pipes. Other existing inspection solutions rely on a limited number of flow metering devices (spot meters) which are installed sparsely across the sewer network. As a result, there are clear indications that less than 2% of the UK network is surveyed every 5 years and that a considerable number of flooding incidents are either unreported or observed with a considerable delay. This prevents the water utilities from developing a proactive maintenance programme which would enable them to achieve zero-failures in terms of sewer flooding.

The project proposed here is formulated to develop new science which underpins the emerging fibre-optic sensing technology platform which can be laid with a robot in the invert of a sewer pipe to sense the flow conditions and continuously monitor pipe deterioration pervasively and to respond to events proactively. Theoretical, numerical modelling and extensive laboratory work will be carried out to understand the fluid-structure interactions between the turbulent flow and turbulence-induced vibration in the fibre cable containment system. The optical signals will be studied, numerically predicted and theoretically explained. New signal processing and pattern recognition algorithms will be developed to link these optical signals to key flow characteristics and to the change in any change structural integrity of the pipe. In addition, field measurements and validation will be carried out with support the lead commercial partner, nuron Ltd, using the new fibre-optic cable system. A key outcome of this work will be: (i) new theoretical understanding how this technology works and be developed towards a much higher technology readiness level; (ii) new, user-friendly software which will incorporate the major theoretical findings and post-processing algorithms that convert the optical signal to the flow characteristics measured distributively along the fibre-optic cable length and understood by the end-user.

The proposal is timely because it will contribute significantly to the need for us to better understand the hydraulic behaviour and conditions of our buried infrastructure in real time and at an unprecedented spatial resolution. The new sensor technology will also enable new theoretical foundations to be developed in the areas of hydraulics, wave propagation, structural health/condition monifoting and computational fluid dynamics.

Planned Impact

This project will result in new fibre-optic cable technology platform with the capability to rapidly survey the hydrodynamics and structural conditions of pipes non-invasively with an unprecedented degree of spatial and temporal resolution and spatial scale. This capability is important for asset management, flood risk, pipe condition change and pollution risk from intermittent discharges in watercourses. The following groups will benefit from this work: (i) short-term (duration of project) - flow survey instrument and sensor developers and manufacturers; (ii) medium-term (up to five years) - water utilities and consultants; and (iii) long-term (five to ten years) - governmental regulators, non-governmental organisations (NGOs) and general public.
1. A sensor manufacturer is involved (see LoS from nuron). This organisation will benefit in terms of a much better physical and mathematical understanding of the link between the hydraulic flow characteristics, turbulence, free surface behaviour in an open channel flow, acoustic waves generated in fibre-optic cable containment system and ability of the signal processing/pattern recognition algorithms to infer accurately the true characteristics of the flow and structural conditions in the pipe from the optical data. Other flow monitoring companies will be engaged via the project workshops. The better understanding of the physics and underpinning mathematics will enable the design more accurate, lower cost flow measurement instruments which will be commercially viable and have high market value. The flexible deployment of the new sensor technology can be achieved by working with water utilities right from the start.
2. The project benefits from the involvement of the USEPA (see LoS) and other non-academic partners (EA, Arup, Severn Trend Water) (through nuron's active links). Their involvement in the steering of the work and provision of data and testing sites will ensure that the outcomes of our work will be of high importance to government and statutory bodies and consultants engaged in water resource and river management. For example, the EA/USEPA have a statutory duty to assess and manage flood risk and discharge in watercourses. This is accomplished by understanding well the sewer and drainage capacity and devising adequate measures to reduce flood/discharge risk. Currently, pipe flow models are used which are calibrated against sparse data collected at a limited number of nodes. The new sensing technology platform to be developed will allow more widespread and higher quality measurement at all flow conditions and at unprecedented spacial and temporal resolution. Accurate monitoring of the spatial and temporal hydraulic changes in pipes is of paramount importance for predicting incidents of urban flooding and pollution discharge in watercourses. Thus our developed technology is likely to be a core tool in EA/USEPA's work by providing spatial hydrodynamic data to assess impact and to prevent incidents of sewerage discharge. The pipe failure and flood risks are assessed by water utilities and by consultancies. The detailed data obtained from fibre-optic sensing will provide new understanding of pipe flow hydraulics for water utilities, consultancies and government statutory bodies involved in the management of urban water infrastructure and catchment areas.
3. The ability to collect low cost flow data with fine spatial and temporal resolution will over the longer term provide a better assessment of the hydraulic capacity of a pipe network and its deterioration rates. This will lead to the improved management by water utilities of their buried assets. NGOs and the general public will benefit in terms of improved flood risk management and better ecological status achieved through provision of better, more plentiful temporal and spatial hydraulic data, which will also raise public awareness of potential ecological impacts of sewer pipe failures.

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