Go to people you trust

Alan Bellenger, one of West's direc¬tors, felt that the good engineer should identify the sort of ground, specify the site investigation with some leeway in case conditions dictate a change, and then approach one or two firms he knows and trusts to do the investi¬gation. He is convinced that many site investigations could be improved if they were better supervised by who¬ever commissions the report. In fact Bellenger puts poor supervision, and accepting the lowest tender, as the principal reasons for bad reports. • "They are rarely supervised with the same degree of tightness that a piling or other contract is," he says. "My general impression is that al¬though site investigations still leave something to be desired, they are im¬proving, and a greater awareness to their importance is developing." Bellinger is not terribly impressed by recommendations made by site in¬vestigation companies on the type of

pile to use. "Firstly they are not terribly good at it. Sec¬ondly, if they have piling company connections then their motives are suspect— one of the reasons why we have decided against operat¬ing in this field is that we didn't want to be in a posit¬ion of diagnosing and pre¬scribing—and thirdly, they tend to be too conservative." Something which particu¬larly irks Bellenger as a pil¬ing contractor—and it is reasonable to suppose that this problem may arise in ' other fields—concerns access to infor¬mation contained in the site report. He maintains that there is still a signifi¬cant number of consulting engineers who treat the site investigation report as if it is top secret. Companies tendering for a job are often faced with a "you can have a look at it if you care to come up" attitude. Bellenger says they would gladly pay for any copy, and that having to base a tender on a glimpse of the document in the consultant's office is ludicrous. Curtis made a point related to this about the way in which consulting engineers have been guilty of withold- ing the pre-amble to the soils report, only allowing the contractor access to the borehole log.

Bellenger's final plea as a contractor was for the site investigation people to take at least one or two boreholes to a substantial depth. "They often reach the load bearing strata and think that's it," he says. "Frequently, if they were to go a few more feet they would be out of it again and into something quite different."

Borehole library

With so many operators in the site investigation business, what is the case for both a central register of SI reports, and a detailed soils map? Bob Curtis feels that a central register would only be a useful service if it was used by people who understood it and its limitations. "It could indicate the directions to look for problems— but site investigations are capable of missing points" he says. Curtis can think of sites of only a few acres which have been developed on different occasions over a number of years, possessing a particular fault which every single site investigation has missed, leav¬ing the joys of discovery to the engineering contractor! Others have roughly the same feelings about a regis¬ter—in favour, but with res¬ervations about the variation in the quality of the inform¬ation available, and the inter¬pretation of it by the users. Enthusiasm for the detailed soils map is markedly less, mainly because of the difficulties of representing three- dimensional information in two di¬mensions. The legend for a detailed map could be so complex as to render it unworkable. However, a lot of borehole data already goes to the Institute of Geological Sciences for its information.

So though the quality of site investi¬gations is improving, how do you protect yourself from being handed a poor report in the interim? "When commissioning a site investi¬gation, go for a more well-established site investigation company and dis¬cuss the project with them." Sound advice and a parting shot from Soil Mechanics, the longest established company in the business.