Discussion: Session 3—testing, instrumentation and construction

S. THORBURN (Thorburn and Partners)

This final session of the symposium which involves mainly the practical aspects of piling will be introduced by Mr Cooke who has studied all of the Papers presented in the two previous sessions for the preparation of his general report.

Two important points emerge from my own assessment of the Papers:

(a) the important influence of construction method on the performance of piles;

(b) the correct behaviour of the piles referred to in the various Papers could not have been determined without proper instrumentation.

In regard to the first point there are many interesting statements on construction made by the various Authors which have not been highlighted in their Papers and I would recommend that these important but inconspicuous statements be examined for their content. As a final point, before I introduce Mr Cooke, I would endorse the remarks made by Mr Hobbs in respect of the cost effectiveness of piling and the need to avoid overconservative designs. Engineers are quite content to accept total building settlements of the order of 35 to 50 mm and yet are concerned when pile tests reveal variations in deflexion at the heads of piles at working load of the order of 2 to 3 mm. We can focus too much attention on the performance of individual piles which are affected, although not seriously, both by variations in the geological structure and by construction.