The construction of the Pen-y-Clip section of the A55 required the construction of an 880 metre long driven tunnel with canopies at each end, the installation of about 2000 ground anchorages to support retaining walls and rock cuttings, and extensive rockfall protection measures on steep sidelong ground. The retaining walls were constructed through unstable ground with the supporting anchorages being installed in deposits ranging from loose scree to microdiorite. The largest wall was nearly 30 metres high and required 758 anchorages. Hydraulic load cells were installed on 150 anchorages and the data from these show a satisfactory performance. Monitoring of the movements of the walls and rock cuttings was carried out using walls and rock cuttings was carried out using conventional surveying techniques and also by photogrammetric methods. The total movements to date have been small, but monitoring will continue in the longer term. Despite the restrictive nature of the site and the difficult ground conditions, the work was completed successfully and ahead of schedule. (A)
Abstract