PAS128 Underground Utility Survey Explained
A PAS128 underground utility survey is a type of survey that aims to locate and map the various
underground utilities and services present in a specific area. PAS128 is a specification developed by
the British Standards Institution to standardize the surveying of underground utilities in the UK.
The purpose is to provide accurate and reliable information about the location and depth of buried
utilities. Such as gas pipelines, water mains, electricity cables, telecommunication cables, and
drainage systems. This information is crucial for construction projects, infrastructure development,
and urban planning. Helping to prevent accidental damage to existing utilities during excavation and
construction activities.
The PAS128 specification outlines several different survey quality levels (Cat A-D). Based on the
survey methods used and the level of confidence in the utility location information obtained. The
levels range from a basic desktop study (Cat D) to an intrusive survey involving ground penetration
(Cat A). The chosen quality level depends on the specific project requirements and the available
budget.
A typical PAS128 underground utility survey involves the following steps:
Desktop Study (Cat D): This initial phase involves gathering existing utility records, as-builts, and
plans from utility companies and relevant authorities. It helps in creating an initial understanding of
the utilities’ location. Providing a basis for planning the subsequent survey stages.
Site Reconnaissance (Cat C): A physical inspection of the site is conducted to visually identify any
visible utility features. Such as manhole covers, valve boxes, inspection chambers etc.
Geophysical Survey (Cat B): Non-intrusive geophysical survey techniques, such as ground-penetrating
radar (GPR) and electromagnetic induction. These are used to detect and map underground utilities.
These methods provide information about the horizontal and vertical position of buried utilities.
Verification (Cat A): Intrusive techniques like trial pits/boreholes may be used to verify the presence,
depth, and condition of specific utilities.
Data Processing and Mapping: The data collected during the survey is processed, analysed, and
compiled into detailed maps, plans, or 3D models that provide a clear representation of the
underground utility layout.
Underground utility surveys reduce the risks associated with striking or damaging buried utilities
during construction and excavation works. By providing accurate and up-to-date utility information, it
helps ensure safety, prevent service disruptions, and minimize costly delays and repairs during
construction projects.