Divergent interests

Sometimes the recommendations of a site report are in conflict with the geographical desirability of the site. The SI may well recommend moving a building to another part of the same site—or not to build there at all if an alternative site is available—while the client could have very sound reasons for wanting to be in a particu¬lar spot.

However, no foundation problem is insoluble; it just means that in poor ground the price for not moving or re-orientating the building could be high.

Back now to Arup. Besides the early involvement of the archeologist, a mining engineer may look in, and the geomorphologist unravels the mass of data before his eyes on available stereo- pair aerial photographs. Much information can be gleaned by walking the area, and by contact with local people. Very important is an appreciation of the topography of the site—a point also made by Soil Mechanics—for, after all, the land form will have achieved equilibrium if it hasn't been recently disturbed, and someone coming along and tearing out the vegetation and skimming the surface disturbs this balance. Foresight is needed to see what conditions will prevail during and after construction.

Above: An unusual application for SI instrumentation—-here Soil Mechanics monitors the ground disturbance caused by demolishing this 250ft-high cooling tower in Cardiff. Photograph by courtesy of CEGB

"We try and understand the geology and land forms; why the topography is the way it is. Understand this, and you can work on how it will change" says Arup. "If you don't appreciate this, then I don't see how you can start. You must totally understand the site."

One final piece of advice from Arup on procedure. "Eighty per cent of engineering failures wouldn't have happened if the engineer responsible had drawn a cross-section, including adjacent buildings, of what he was proposing to do above and below ground. He would often see what he is intending to put up simply won't work. All too often the engineer dives straight in and gets too close to the job to view it objectively."

Valuable comments

One additional advantage of the "Arup intimate involvement" is that the supervising engineer is at hand after the report is produced to sit-in on the foundation design part of the project. He can often provide valuable comments during this phase. Some¬times, where a site investigation com¬pany is interpreting the results, any consultation obligations terminate with the handing over of the report. However, it must be remembered that the "no stone unturned" ap¬proach is not always applicable, and Geoff Child was not alone in noting that the whole exercise must be kept in perspective. The complexity of the approach could diminish in proportion to the size of the structure and site. From his point of view, Child was able to summarise the factors needing correct assessment for a good site investigation to result

□what the project is—the quality of SI you need

□who the client is—how conversant with the prob¬lem is he?

□the ground conditions— their consistency will de¬termine the accuracy of projections based on the boreholes.

Very little has been said so far about the smaller site investigation firms. Some of them are very good at the -' practical side of the exercise, but they are likely to experience prob¬lems in making the grade when they become more ambitious and want to plan and interpret the investigation. Unfortunately there are a number of "fast buck" operators around thriving on the tendering system, and these make it more difficult for the expanding company with more commendable motives to find its feet. How does the civil engineering con¬tractor, the one who puts all his effort to the test, feel about the sub¬ject?

Foundations specialist West's Piling and Construction was able to reaffirm from its own experience, site investi¬gations were frequently unsatisfactory. Off the top of his head one engineer estimated some 15 per cent had no value at all, with a far higher percent¬age having significant shortcomings.