Important new research on the reliability of the generally available technology for detecting and gelocating underground utility infrastructure and the costs of hitting utilities during excavation (known as strikes in the UK) was presented at the Year in Infrastructure 2016 conference in London. Dr. Nicole Metje, Professor of Geotechnical Engineering at the University of Birmingham, presented some of her most recent research on a major problem affecting the construction industry worldwide.
Background: utility strikes in the UK
About 4 million excavations are carried out on the UK road network each year to install or repair buried utility pipes and cables. Not knowing the location of buried assets causes practical problems that increase costs and delay projects, but more importantly, it increases the risk of injury for utility owners, contractors and road users. The problems associated with inaccurate location of buried pipes and cables are serious and are rapidly worsening due to the increasing density of underground infrastructure in major urban areas. In the U.S. it is estimated that an underground utility is hit about every minute and underground utility conflicts and relocations are the number one cause for project delays during road construction.
The standard tools in the U.K. for detecting underground utilities are the cable avoidance tool known as CAT. The CAT can detect signals naturally radiating from metallic services or in conjunction with a Genny that applies a distinctive signal that the CAT can detect. The adoption of ground penetrating radar is increasing, but compared to CAT it remains relatively expensive and requires trained operators.
Underground asset detection is the last frontier of remote sensing. In the U.K. it has been perceived as a serious problem since at least a decade ago. The Mapping the Underworld (MTU) project was initiated in 2004 to develop a multi-sensor platform to locate and map in 3-D the location of all buried utility assets - without excavation. The 10-year research program, which was largely funded by the Engineering and Physical Sciences Research Council (EPSRC), involves the University of Birmingham, University of Bath, British Geological Society, Engineering and Physical Sciences Research Council (EPSRC), Univeristy of Leeds, Newcastle University, University of Sheffield, University of Southampton, and UKWIR. The project concluded that a combination of multiple technologies is essential for the reliable detection of the buried assets. The project aimed to develop a remote sensing platform that combined several detection technologies together with software that optimizes the combined data. To achieve a 100% location success rate without disturbing the ground is the 'holy grail' of underground remote sensing. The benefits of knowing where underground infrastructure are well documented.
Since then, a second major multi-disciplinary, multi-university research project, Assessing the Underworld (ATU) has been funded, largely by the EPSRC. The project aims to create prototype multi-sensor devices that will enable the condition of underground assets to be assessed remotely without excavation. The technologies include above ground remote sensing and robotic devices that can be deployed in a water distribution or sewer pipeline.
In 2012 the U.K. the civil engineering contractor's association CECA conducted a survey of its members on the topic of underground strikes. It asked questions about the technologies used and whether the respondent has internal processes for tracking and estimating the costs associated with utility strikes. I have paraphrased the questions.
|Does your organization quantify the direct costs of utility strikes on a regular basis ?||Yes 57%||No 43%|
|Do you track and quantify other costs (indirect and/or social) incurred during service strikes ?||Yes 29%||No 71%|
|Do you have a separate programam or project for determing and recording the location of underground utilities program ?||Yes 14%||No 86%|
|Does your field staff use a Genny as much as it should be ?||Yes 14%||No 86%|
|Do you think underground utilities would still be damaged during excavation if your staff used a Genny as often as it could be ?||Yes 0%||No 100%|
This suggests that even the limited (see below) tools available today for underground detection are not used to their fullest extent. The direct costs of utility strikes are still not quantified and tracked in many firms, and very few firms are aware of the indirect costs associated with utility strikes. Probably as a result of not knowing the costs, very few firms have an explicit program for geolocating underground utilities.
Risk of underground utility strikes
Dr. Metje presented new results based on her research on utility strikes in the U.K. She pointed put that unlike the U.S. where collecting statistics on underground hits is relatively easy, in the U.K. it is a challenge. In spite of the obstacles, she managed to collect data on 3348 strikes defined as incidents during excavation which involved damage to underground utilities. Some of the very interesting results of the analysis include
- Of 255 strikes where pre-excavation CAT scans had been carried out, in 52% of the cases the utility had been detected before the strike.
- Of 187 strikes where utility plans/drawings (as-builts) had been reviewed before excavation, in 48% of the cases the utilities hit were shown on the plans.
- Of 89 strikes where the plans/drawings (as-builts) showed the utility, in 84% of the cases respondents reported that the location of the utility was inaccurately plotted. 16% said it was accurate.
In other words even when it is known that there is utility infrastructure underground, there is still a very significant risk of hitting it - perhaps because its location is not known accurately enough. It also provides further evidence that, in general, as-builts cannot be relied on, either because they are "as-designed" or because they have not been maintained and do not record modifications that may have been made since the infrastructure was first built.
Cost of hitting underground utilities
Dr. Metje presented important results on the direct costs of utility strikes in the U.K.
However, Dr. Metje has found that the true costs associated with utility strikes is much higher than this. Direct costs include the costs of sending a crew to assess and repair the damaged pipe or cable. Indirect costs include the impact of traffic disruption as a result of the strike, any injuries and other impacts on the health of the workers directly involved or people in the immediate neighbourhood, and the lost custom that businesses would have experienced as a result of the traffic disruption. Dr Metje's research suggests that the true cost much larger than the direct cost. Her estimate is that the true cost is about 30 times the direct cost. This is a startling result which indicates that the cost to society of underground utility strikes is much, much larger than is generally believed.
Reliability of underground utility detection
In the U.S. the ASCE 38-02 - Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data is widely used for classifying location information about underground infrastructure according to its estimated reliability. I've blogged about a major national project in France aimed at classifying information about all of France's underground utility infrastructure according to a standard that specifies absolute accuracy (< 40 cm, 40 cm - 1.5 m, >1.5 m).
In the U.K. Publicly Available Specification (PAS) 128 governs the recording of the location of underground utilities. PAS 128 was developed under the auspices of the British Standards Institution (BSI) and sponsored by the Institution of Civil Engineers (ICE). PAS 128 is aimed at the practitioner - surveyors who make their living detecting and reporting the location of underground utilties for construction contractors and utilities. The primary objective is to reduce risk for construction contractors. In the UK, unlike the U.S. and Canada where we have one-call centres, in the U.K. if a utility is disrupted by a construction project, the liability lies entirely with the contractor.
PAS128 has aspects of both the U.S. and French system. It is similar to the US ASCE standard in that codes (A) through (D) relates to how the location was captured. The British standard is different in that it adds sub-categories B1 through B4 which specify the absolute precision of the remote-sensed location.
QL D - Location of underground structures determined by a review of existing utility (paper) records
QL C - A physical reconnaissance of the site has been performed identifying features of the network are visible above ground
QL B - Remote detection technology such as electromagnetic or ground penetrating radar have been used to detect the location of the underground facilities. There is a sub-classfication B1-B4 that specifies the estimated precision of the measurements. For example, B3 corresponds to +/- 0.5 meters.
QL A - Verification, typically by potholing
Dr. Metje reported revealing research aimed at assessing the PAS128 standard and also validating the reliability of the MTU (Mapping The Underworld) sensor technologies on a site where underground truth could be determined. Five commercial companies were invited to conduct a utility survey of the chosen area to PAS128 standard. The firms were asked to survey the underground utilities in the same area and report location in the form of a map. This was compared with the results of a survey conducted with the MTU platform. The firms agreed on the location of wastewater and storm sewers and water utilities (pipes). But in the case of the location of telecom and electric cables there was substantial disagreement - the total length of telecom and electricity cables detected by different firms varied widely, from 90 to 240 meters. This is a startling indication of the risk associated with existing underground utility detection technologies.
A new standard relating to underground utility detection is expected to be released in early 2017. PAS 256 (Buried services – Collection, recording and sharing of location information data – Code of Practice) governs data sharing.