The project

Structural Soils completed embankment stabilisation work at Afon y Bala Embankment, North Wales. Our remit was to obtain geotechnical information and provide long-term ground monitoring to assist designing an engineering solution to stabilise the upstream face of the embankment, which has shown continual downslope movement since the embankment failure in 1978.

Project background

Structural Soils completed a ground investigation at Dinorwig Power Station, North Wales. Our remit was to obtain geotechnical information and provide long-term ground monitoring to assist designing an engineering solution to stabilise the upstream face of an embankment, which has shown continual downslope movement since a failure in 1978.

Scope of work

  • sonic drilled boreholes
  • sonic pre-bore boreholes through fill material for in situ CPTS and pressuremeter testing
  • installation of vibrating wire piezometers (VWPs), inclinometer casings, automated shape array inclinometers, manual and automated rod extensometers

The project coincided with shutting down the power station to enable major refurbishment of the power generating plant. It was vital that the ground investigation was completed during this 10-week period. Draining of the lower reservoir provided the necessary access to the base and slopes of the dam to undertake the ground investigation. We completed the project one week early, negating further shutdowns for recommissioning the power station. Structural Soil’s multi-purpose sonic, duel head drilling rigs completed the drilling and sampling of the boreholes. The rigs were custom specified by SSL to enable sampling of overburden soils by sonic (also known as resonance) drilling. Slate waste tailing, consolidated clays/silts, peat and glacial-fluvial deposits were sampled. The sonic rigs were also used to pre-bore CPT locations. This was due to the engineered slate waste material across the site and would be unsuitable to pish the CPT through.

Structural Soils projects - Dinorwig, Wales - image

Value added

A key deliverable involved providing long-term ground monitoring to assist in designing an engineering solution to stabilise the upstream face of the embankment. The unique setting of the boreholes being drilled in the reservoir meant that conventional ‘manual’ monitoring of instrumentation could not be carried out. Therefore, remote monitoring solutions were installed in the boreholes susceptible to regular flooding. These included VWPs (vibrating wire piezometers) measuring pore water pressures at multiple depths; rod extensometers measuring vertical ground movements at depth; and shape array inclinometers measuring horizontal ground movements.

Cables from all the installations were trenched across the site and brought together to a single monitoring junction box where the data signals are sent wirelessly to an internet gateway. The gateway is powered by a battery and re-charged using a solar panel. The data from the monitoring installations is available for online viewing and download.