The good news is that the danger to human life and the risk of potentially millions of pounds of physical and environmental damages incurred as a result of a utility strike is completely avoidable. With the right planning and investigation, utility strikes are preventable even when construction works are taking place in densely and highly populated urban environments.
The key to avoiding accidental utility strikes is first locating and identifying all underground utilities in the vicinity of works, and then – if carrying out construction works near to these assets is inescapable – having an appropriate monitoring system in place to ensure minimal impact to these assets as construction progresses.
The importance of detecting underground utilities
According to HSG247 guidance, it is recommended that an underground utility detection survey is carried out prior to construction work taking place on or near buried services. It is highly recommended that detection, verification and location of underground utilities is undertaken in accordance with the British Standards Institution’s (BSI) PAS128 specification.
By identifying the location of buried services, contractors and developers are able to avoid service strikes, which not only prevents disruption and costly rescheduling, but more importantly protects the health and safety of those carrying out the works.
While the benefits of carrying out accurate utility tracing are obvious, clients must also be aware of the potential risks of relying on survey data that is out of date. Any results that are more than three months old are generally considered as historical, as this length of time may have allowed for the installation of new utilities since those surveys were undertaken. Therefore, ensuring that utility survey information is up-to-date is of paramount importance.
Utility surveys - techniques used
SOCOTEC’s team of surveyors conduct desktop studies and, when required, site reconnaissance prior to each underground utility survey to determine where buried services are located. All utility surveys are undertaken in line with BSI PAS128, the specification for underground utility detection, verification and location. This ensures that the survey data can be relied upon fully and permits all construction and utility-based works to be carried out safely and with confidence.
Implementing state-of-the-art technology and cutting-edge software to carry out underground utility tracing surveys, SOCOTEC’s survey teams make use of a variety of methods depending on the soil conditions and the expected buried utilities. Examples of these methods include:
- Ground Penetration/Probing Radar (GPR) – uses electromagnetic radiation to locate buried objects such as plastic pipes and cables that are foreign to the surrounding environment, identifying any changes or interfaces between different media below the ground. This comprises 1m spacing grids (dependent on the PAS128 specification chosen by the client), which can either be used with an on-site mark out or post processed back in the office. While this method cannot determine the material of the object in question, it is highly recommended for those who wish to obtain specific information relating to the underground environment
- Stream C – a real-time 3D mapping tool used to produce a three-dimensional construction of the underground network in one scan. Stream C facilitates large underground utility surveys via its towing kit, or smaller surveys due to its compact size. SOCOTEC’s Ground Investigation team is one of the only businesses to adopt Stream C technology, which enhances productivity, data accuracy and efficiency as the survey need only be carried out in one direction
- Radio Frequency Location (RFL) – as the most ‘conventional’ form of utility mapping technology, RFL provides 3D maps to automatically detect pipes, cables and drainage runs. Used to detect electricity/communication cables, water, gas, fuel and vent pipes, SOCOTEC delivers an advanced form of Cable Avoidance Tool & Signal Generator (often referred to as Cat and Genny).
As well as the above utility detection methods, SOCOTEC uses RD8000s for electromagnetic works, clip and clamps to locate cables that are either visible or within the manhole cover, as well as power and radio sweeps for any utilities that are not visible. Leica GPS and/or total stations can also be used to record the data, which can then be drawn up in AutoCAD back at the office.
Benefits of utility tracing
Locating and identifying utilities is undeniably an essential requirement for any proposed construction project, especially for contractors operating in urban environments who may have to carry out works around a maze of assorted third-party utilities assets. Utility surveys provide a clear understanding of the existing assets within the planned construction zone from the outset. This knowledge can allow either for design alterations to avoid them entirely, or – if design changes are not possible and invasive works are required close to existing utilities – it can help to identify assets which require further investigation and monitoring to minimise impact as construction progresses.
Preventing indirect damage to assets with monitoring
There are risks involved in any construction project, and the uncertainty of the ground’s behaviour and the impact that this can have on existing third-party assets is one significant risk which can be greatly reduced through geotechnical and structural monitoring.
Excavation work is often a fundamental part of most construction projects. When excavating a site, stresses within the underlying and surrounding soils are changed, and this can have an impact on adjacent buried assets, such as pipes, cables or tunnels. Therefore, before works can begin, contractors must establish the location of third-party assets and understand the composition of the soils surrounding those assets. This data is used to predict how the ground above and adjacent to an asset is likely to behave as construction advances, as well as what damage this might induce.
Monitoring direct and indirect parameters such as strain, deformation, displacement and vibration warns of any likely damage, allowing contractors to make informed decisions to minimise risk to the assets, the project’s budget and programme and, most importantly, to people.
The main benefits of this best-practice approach to monitoring include:
- Avoiding overly conservative design approaches when related to the possible impacts to an asset – in some cases, monitoring can help identify where construction rates can be increased or when invasive works can be carried out closer to an asset. Having access to near real-time monitoring data allows contractors to make informed decisions about the progression of a project, which can positively impact timescales and budget
- Understanding what normal looks like – prior to any works taking place, baseline monitoring helps to determine suitable trigger limits so that only changes that are outside of the norm are reported and actioned
- Confidence – asset owners can have peace of mind knowing that the works are not posing a risk to their assets and that their customers will not have their essential services – such as gas, electricity and water – interrupted.
As aforementioned, underground utility detection technology and processes are the key to avoiding damage to utility assets, as they are able to locate and identify all underground utilities in the vicinity of any construction works. Carrying out excavation and construction works in close proximity to existing utility assets is often unavoidable, especially when developments are taking place in densely packed urban environments. To ensure the influence of these works on third-party assets is kept to a minimum acceptable level, geotechnical and structural monitoring is required to predict the behaviour of the surrounding ground and the indirect consequences of any movement to utilities assets.
If you would like to speak to SOCOTEC regarding any of the above utility detection services, please get in touch.
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