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Situación inicial
The scheme involved rockfall protection works below an existing chalk cliff. The site is part of an old chalk quarry, and previous works have been undertaken across the site to address rockfall issues.
The geology is that of the Seaford Chalk Formation. Previous investigations describe the rock as extremely weak to weak low to medium-density chalk with occasional iron staining and flint seams. Generally, bedding discontinuities dip into the cliffs, favouring stability.
Following a failure along the cliff line to the east, the decision was made to install rockfall protection measures below the promontory of the cliff above the road. The chalk on the 'nose' of the slope is around 60 degrees with a maximum height of 35 metres and heights of 12 - 16 metres on its east and west faces where the slope angle increases to near vertical.
Small amounts of rockfall were noted, with typical block sizes between 25 - 100 mm.
Descripción
The site owners instructed RSK Geosciences to undertake a rockfall assessment of the site and provide recommended remediation measures. This came in the form of a Rock Fall Catch Fence Design and Specification Report, which included a detailed rockfall analysis of the site using the software RocFall.
Following rockfall analysis modelling, a rockfall barrier was recommended as an appropriate solution. Based on modelling, the appropriate capacity and height of this system was a 500 kJ three-meter high barrier. Due to site conditions and the reduced installation time required, the decision was made for the barrier not to have upslope anchors, thus saving time on site with less drilling required. The chosen rockfall barrier was a GBE-500A-R, 60 meters in length, with seven fence posts.
Geobrugg worked with RSK during the design to provide anchor force datasheets for the chosen barrier to assist with anchor length calculations and provide technical datasheets for the chosen flexheads (Type IV) to suit the bar used on site (R38-500).
The contractor chosen to undertake the works was CAN Geotechnical Ltd. CAN drilled anchors for the fence posts and lateral anchors before casting concrete bases for the base plates. Installation of the flexheads on the lateral anchors followed, and then the fence posts were lifted into place and secured. Ropes were installed before the mesh panels were opened, and final fittings were added. Following a visit to site, Geobrugg assisted with a slight change to the fence arrangement due to a change of angle and additional downslope rope requirement. We were able to work swiftly with the contractor to ensure no delays occurred on site.
The installation ran smoothly, and Geobrugg attended the site to assist with the installation and check the final system.
País / Región
Reino Unido
Cliente
CAN Geotechnical Ltd
Ingeniería
Subcontratista
Objeto protegido
Carretera
Protección contra la corrosión
GEOBRUGG SUPERCOATING
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