Nearly fifty members and guests gathered at the East Mendips Study Centre to hear David Gibson, business development manager with BAM Ritchies, give a talk entitled 'Rock and Soil Slope Stabilisation and Protection - Best Practice'. He began by stating the requirements of the 1999 Regulations in terms of inspection, appraisal and assessment and the need to provide adequate and economic solutions. He outlined the technology now available to assess possible failure mechanisms, such as stereo photography and laser scanning. Dedicated software packages can now determine the optimum forces at anchor points as a function of the geotechnical parameters.

David explained the standard methods of stabilisation such as scaling and pre-splitting. He then went on to describe active solutions such as rock bolting and ground anchors. One of the major issues associated with these techniques has been corrosion. However modern manufacturing techniques and the use of new materials can now provide significantly longer life.

David then explained best practice in the use of soil nailing as an example of a passive solution. This is a similar method to anchoring but is installed with little or no tension. Its use has increased over the years largely as a result of new guidance produced by CIRIA.

Access is a critical aspect of the operation and David described how advances in technology such as boom-mounted long reach excavators and remotely controlled rigs have reduced the need for hand-held drilling. This has led to a reduction in the incidence of HAVS. For some undertakings Ritchies have developed their own equipment to enable them to drill even on near vertical slopes.

David outlined the methods of soil retention using geo-textiles and wire mesh, giving examples of how it had been employed on railway embankments and motorways, notably the M4 between Cardiff and Newport. Using such methods in a rail cutting at Flax Bourton, had reduced the costs from £12 million to £6 million compared to more conventional techniques. It also had the added advantages of not taking possession of the line whilst the work was being carried out and the fact it could be seeded to produce a natural looking slope.

David concluded his talk by considering the issue of rock fall protection. He said it was often more economic to catch rock rather than try to support it. He described the techniques now available which were capable of doing this. To illustrate the point he showed a system being subjected to a test where a 16 tonne weight was dropped onto it from a height of 32m! In a quarry situation this method could be employed to reduce berm widths or even eliminate them.

Throughout, David illustrated his talk with many examples from all over the world. A lively question and answer session concluded a very informative and thought provoking evening. Kevin Sargant proposed the vote of thanks to a very accomplished and knowledgeable speaker.