TECHNICAL | TUNNELLING IMPACTS
IMPACTS ON UTILITY PIPELINES
TUNNELLING AND GENERAL CONSTRUCTION
Dr Cheong Kin Gary Choy and Dr Barry New (both of Geotechnical Consulting Group, UK) provide a broad guide and structure to assess the impacts on utility pipelines from various tunnelling and construction activities
1 INTRODUCTION This paper develops and extends the content of the 2017 Harding Memorial lecture (New, 2019) and reflects the development of techniques used on numerous recent projects including HS2 and Thames Tideway. It is inevitable that many construction works will give rise to ground movements which can have adverse impacts on third party assets if these works are not carefully designed, planned and carried out: the presence of sensitive, vulnerable or ageing assets exacerbates this problem. The impact of construction works on buildings throughout the world have been well-documented but there is a lack of literature focusing on the impacts on utility assets. Through the authors’ longstanding engagement with
the Research Working Group (WG2) of the International Tunnelling and Underground Space Association (ITA), it has become apparent that the approaches adopted by both utilities and developers in different countries vary significantly and are influenced by the prevailing social and legal frameworks. The objective of this paper is to provide a broad
guide to the assessment of utility pipelines which are subject to impact from various construction activities. It is intended to provide a structure to impact assessment which includes utility requirements, components of pipeline risk assessment, pipe failure mechanism, masonry, concept of impact strain, and the staged assessment process. The presented methods and strategies are based on the authors’ experience, particularly in London and the Thames Valley. The more risk-based approach puts an emphasis on rationalising the assessment process to reflect the uncertainties about ground and asset conditions, consideration of the consequence of asset failures (see extent of damages shown on Figure 1), and implementation of control and mitigation measures.
12 | February 2022 The paper cannot cover all types of utility assets
and the various conditions encountered throughout the world. However, it is intended to be as informative as possible so that assessors will be able to adapt the presented principles and methods to suit local conditions and construction methods.
2 UTILITY REQUIREMENTS There are generally three key utility requirements that will have to be considered by developers, designers and contractors throughout the design and construction phases of new development schemes: ● The utility must be in compliance with its statutory and regulatory obligations. In particular, the serviceability to customers should not be threatened in both short and long term. The failure to protect an asset from any construction damage could result in serious health and safety issues, substantial third-party damages, and penalties from regulators.
● Whole-life asset value should be maintained. There should be no damage, loss of capacity or downgrade of an asset to ensure its value is retained to protect stakeholders interests.
● The proposed works should not inhibit or prevent any maintenance or repair works that are required for the asset.
In order to meet these key requirements, developers, designers and contractors are expected to undertake pipeline risk assessments to inform utilities regarding the likely risk to their assets posed by the proposed development, and how the risk might be eliminated, minimised or otherwise mitigated. The assessment cannot be completed without essential information from the utility which includes asset maps (showing the ‘indicative’ alignment and material of the assets); repair
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