Project Sheet: Cwrt Dyffryn
- Cartrefi Conwy
- Site Investigation
- Desk Study
- Letter report to provide geotechnical options
- Detailed design, drawings and specification for the preferred remedial option
Description of Project
GroundSolve Ltd were approached by Cartrefi Conwy with concerns about an unstable slope behind one of their properties in the Cwrt Dyffryn Cul de Sac in Old Colwyn, which backs onto Nant-Y-Ffynnon.
Significant loss of land had been observed to the rear of the property and cracks noted on the driveway. The bank was densely vegetated, approximately 5m high and at a gradient of 40º.
GroundSolve Ltd supervised the excavation of boreholes and inspection pits and sent the samples to a laboratory for physical and chemical analysis. The investigation confirmed that the ground conditions comprised glacial till, with a thin veneer of made ground at surface, probably placed to create space for the construction of a driveway for the properties.
The ground was subsiding next to the drive to No 3 Cwrt Dyffryn due to the lack of lateral support from the made ground on the river bank. It was concluded that the cause of the ground instability was due to the over steepness of the slope and lack of compaction of the made ground. In addition, erosion at the base of the slope by the river was causing shallow creep, resulting in the failure of the ground surface.
The improvement of the slope stability was considered in two ways:
- Stabilising the entire slope - a very costly exercise and would require the felling of mature trees and the construction of a new retaining wall
- Stabilising the upper slope independently of the river bank – this is focusing on the initial problem facing the parking area of the property and is a much more cost-effective solution.
The chosen method used for stabilising the slope was as follows:
- The removal of the existing surfacing and fencing;
- Construction of a concrete retaining wall;
- Reinstating the surface.
The work involved the construction of a concrete retaining wall at the crest of the river bank. Some of the existing slope also required trimming on the downslope side of the retaining wall.