BDA Webinar – May 2021 – “Hydrogeological Investigations for Construction Works” – Reviewed

May 14, 2021

May’s British Drilling Association (BDA) Webinar took place 13^th May 2021, with William Powrie, Professor of Geotechnical Engineering, University of Southampton and Toby Roberts, Chair WJ Group looking at hydrogeological investigations typically undertaken to supplement geotechnical investigations for construction projects where impacts from groundwater are anticipated.

Specifically, the webinar drew on material from the forthcoming Geological Society Publication Engineering Geology of Groundwater in Design and Construction: Chapter 6. Observational Models: Quantifying the Conceptual Model through Investigation co-authored by the presenters together with Mark Lee (Atkins).

After introductions, the presentation began with a look at investigation objectives, methods and phasing, before considering key hydrogeological characteristics, notably permeability. Soils may be anisotropic due to layering with permeability typically controlled by particle size. Intact rock may be of low permeability with the permeability of a rock mass typically controlled by jointing. As a result, permeability is a scale dependent parameter and examples were presented of the impact of both small and large scale inhomogeneities. The various methods of measuring permeability were reviewed and rated.

The drainage mechanisms of granular soils were discussed as well as storage coefficient and common groundwater regimes. Particular emphasis was given to boundary conditions, well yields and aquifer far field recharge or barrier boundaries, which often the control drawdown response and distance of influence. It was noted that a good understanding of boundary conditions is a prerequisite for useful numerical modelling of a groundwater system.

The presentation went on to note that the standards for pumping tests, BS ISO 14686: 2003 Hydrometric determinations and BS EN ISO 22282-4: 2012 Geohydraulic testing – Pumping tests, both focus on procedures for single well pumping tests which were briefly reviewed. This was followed by a series of examples of alternative pumping test strategies, using one or more wells, to address groundwater construction issues which commonly arise in a range of hydrogeological settings.

The presentation concluded with several key takeaways:

• Assessment of permeability is difficult!
• Permeability is a scale dependent parameter.
• Borehole and lab tests for permeability have significant limitations.
• Boundary conditions, at the well and far field, are commonly important drivers.
• Single well pump tests are valuable especially in rock but…
• …may not answer all the relevant questions – other pump test strategies can be considered.

The presentation concluded with a questions and answer session.

To listen/view the recording, visit – https://vimeo.com/548851620