In our last article, we began to consider the incorporation of data from archaeological contractors into the BIM process for large infrastructure projects and looked at the first of the three broad phases of archaeological work undertaken during CAPEX; assessment of known archaeological assets
In this article, we discuss the remaining two phases of archaeological works undertaken during construction: evaluation of the potential archaeology within the scheme, and finally, mitigation and monitoring during construction, and look at how they can contribute to the BIM.
Evaluation of potential archaeological remains
During the initial analysis phase we considered the impact of the development on the historic environment and evaluated the risk of encountering unknown archaeological remains. This information is used to inform a methodology for the next phases of work, the first being evaluation. The evaluation phase serves to gain an understanding of the archaeology actually present in the scheme once the projects’ footprint has been finalised.
Whereas the initial analysis phase is undertaken without breaking ground the evaluation and mitigation/monitoring phases are intrusive, however, the premises defined in the previous article still apply; that the archaeological record produced does not need to be shared through BIM, it is the sharing of key information regarding risk and timescales that can bring increased efficiency with other members of the construction team.
An archaeological evaluation serves to ground-truth the potential archaeology identified during the assessment stage by using targeted trenching, or where there is potential for archaeological remains but no current evidence that they are present, by systematically sampling areas using regular trench arrays.
As the evaluation is done as a precursor to any construction it is often the case that the archaeologists are the first contractors to break ground and bring plant to the site. From our experience there are common logistical problems that are experienced at this stage that could be alleviated through the sharing of data in BIM, reducing stand-down time and programme slippage. Examples include; the adding of proposed trenching arrays to the BIM so that locations can be checked for clashes with services and structures against all available data that have been compiled for the project, reducing the likelihood for delays whilst trenches are relocated; or it allows for the tracking of potential plant movements, giving the most efficient possible movement of machines.
Mitigation and monitoring
Once the data from the evaluation has been reported upon, it is then used to create a methodology to record the archaeology during construction of the scheme through three primary strategies: mitigation; strip, map and sample; or watching brief. The first two techniques are often undertaken at the start of the main construction phase, in an attempt to work ahead of the other contractors, and involve the archaeological contractor stripping high-potential areas of the scheme. The mitigation of an area is a more intensive strategy of archaeological recording than a strip, map and sample. A watching brief is undertaken in low-risk areas, whilst they are being stripped by a contractor, as part of the normal construction programme; an archaeologist is required to be present to monitor the stripping to identify any archaeological remains, should they be exposed, so that they can be recorded appropriately.
The identification of excavation areas often happens after the construction programme has been established; if an archaeological site is identified during the monitoring phase as requiring excavation, then construction could be well underway. By integrating the evolving archaeological plan of works into a BIM, analysis can be made of how this affects the overall programme and movement of plant, to avoid contractors attempting to access areas unavailable due to archaeological works and reduce unnecessary standing time. The integration would also aid with the scheduling of archaeologists for monitoring; it can be the case that the need to have an archaeologist present is realised immediately prior to stripping, and delays can occur whilst one is dispatched. By integrating the planning conditions applied to a site into the BIM, a better understanding can be had of the requirements.
Hopefully, we have demonstrated over the last two articles that by exchanging data between the archaeological contractor and other members of the construction team, greater efficiency can be brought, not only to the work of the archaeologist, but to those working on the scheme alongside them.
We’ve considered the broad pattern of archaeological work across a large infrastructure project from design to construction and how the integration of pertinent data can have positive effects on a scheme of works.
By taking a thoughtful approach to data integration, and not flooding a BIM with the archaeological record, archaeologists can provide a positive outcome for efficiency during construction.
Chris Breeden
Senior Geomatics Officer
Wessex Archaeology
Tel: 0114 255 9774
