Landslide on B4570 Treforgan, Llangoedmor


Burroughs worked in partnership with Earth Science Partnership to undertake extensive investigations and remedial designs following a landslip on the B4570 in Ceredigion in South West Wales.

Movement had been occurring on the B4570 Treforgan, near Cardigan over a period of years. The ongoing movement and speed of the final failure resulted in the road’s closure and extensive traffic diversions. It was vital that a robust remediation design was produced swiftly so that the road could be safely reopened to traffic.

Ceredigion County Council instructed the design team to undertake a Preliminary Sources Study Report, Ground Investigation Scoping Report, Ground Investigation report and Geotechnical Design Report in line with CD-622 (2019). Additionally, a site investigation was carried out which enabled and Options Report for remediation to be produced.

The ground investigations, which comprised dynamic sampling with rotary coring follow on, windowless sampling and trial pitting had to confirm the ground model and obtain sufficient information to enable an Options Report to be produced. Information was also obtained to enable design of a suitable remediation scheme at the site.

A conceptual ground model of the site and surrounding area was generated and generally showed Landslide deposits underlying the road which in turn was underlain by a variable thickness of Glaciolacustrine Deposits which are fine-grained soils laid down in a post-glacial lake that covered the surrounding area and lower valleys.

The design team produced a comprehensive Options Report and worked collaboratively with the Client, Ceredigion County Council, to select the preferred remediation design solution. Burroughs then worked in partnership with Earth Science Partnership to provide a design package.

Burroughs carried out all highways and drainage design elements including cut-off drains to lower and control groundwater levels. Burroughs also designed protection to the base of the slope adjacent to a watercourse.

The design team supported the client team to produce and oversee the procurement process and contract to appoint a local contractor to undertake the remedial works. The project was completed successfully and the road reopened to traffic.

Client / Project TEam

Earth Science Partnership Ltd / Ceredigion County Council