Assessing geotechnical constraints on the development of Ulster Canal Greenway Phase 2

Last week, we spent two days carrying out a walkover survey of the disused Ulster Canal alignment between Smithborough in Co. Monaghan and Middletown in Co. Armagh with Clandillon Civil Consulting. Our task was to identify and map potential geotechnical and geological constraints to the development of this very interesting 22km cross border greenway project, to feed in to a wider technical scoping study for the project under preparation by Clandillon Civil Consulting. The project is supported by the European Union’s INTERREG VA Programme, managed by the Special EU Programmes Body (SEUPB).

The canal alignment is quite overgrown and difficult to access but the views were beautiful and the industrial heritage of this unusually narrow canal is fascinating.

The canal’s original engineers and surveyors chose an optimal route, threading the canal between the local drumlins and moraines. This way, the canal follows the edge of the low-lying alluvial deposits between the drumlins and moraines, minimising the need for locks, while keeping the foundations in the competent glacial deposits at the toe of the adjacent slopes.

Phase 2 of the Ulster Canal Greenway, due to open in 2020, will make a fine addition to Ireland’s growing collection of greenways.

Ground investigation in Co. Monaghan

We recently commissioned a ground investigation in Co. Monaghan to support the design of a sports field. There is a deep cut into a slope at one end of the sports field, and using information from the recently-updated Geological Survey of Ireland (GSI) Quaternary Data Viewer we could begin to develop an understanding of the likely geology at desk study stage and make an informed prediction that overburden would extend to a significant depth.  The prediction was correct in this case and drilling encountered overburden of glacial till to the planned investigation depth.

Monaghan ground investigation

The latest GSI Quaternary mapping suggests the site is a drumlinised ribbed moraine. Current knowledge suggests that, in the region of interest, the transition from ribbed moraine (yellow areas in the image below) to drumlin bedform (magenta lines) may be related to ice movement increasing in velocity at this location during deposition. A lot of what we can say about the glacial landscape left behind in warmer places is informed by observations of current glacier movements in colder places, and the paper by Johnson et al. on observations of an active drumlin field in Iceland is a fascinating read on the topic. As with any project which involves an element of ground risk, an understanding of both the geological background of the site and the geotechnical properties of the materials there today is essential to achieving a reliable design.

Screenshot of GSI data plotted in QGIS