I was interested to read Sharon Rose's article 'Self-certification: the way ahead?' in GE's supplement on the geotechnics of the CTRL (May 02), and would like to comment on the applicability of self-certification when the observational method (OM) is used. By OM I mean the full eight-step procedure formulated by Ralph Peck in his 1969 Rankine Lecture.
It seems to me that in this scenario 'a well-skilled workforce' is only part of the need. It is crucial that the designer's entire eight-step series of judgements is communicated to the personnel who will continue the OM procedure into the field phase. If, as will normally be the case, this cannot be done in a design report or in a construction specification, individuals who are intimately familiar with the designer's judgements must be in the field.
In design/build situations, this is straightforward. However, in design/tender/construct situations, surely the designer must have a representative in the field, or a very special effort must be made by the designer to communicate his/her judgements to the contractor, who in turn must have motivated and skilled geotechnical people on the site.
In the British Tunnelling Society's annual debate, held in March, the proposed motion was 'Self-certification is dangerous for tunnelling'. Sir Alan Muir Wood, who seconded the motion, pointed out 'the need for continuity from design into construction', and that one of the weaknesses of self-certification is 'the need for the designer to undertake observations to confirm that conditions conform with the design assumptions' [my italics].
Let us maximise co-operation in the field, including partnering and self-certification where appropriate, but let us not lose sight of the special and crucial needs when OM is adopted.
John Dunnicliff, geotechnical instrumentation consultant, Devon