"Resettlement requirements: feasible and affordable?"
Some 130 interested parties attended the symposium "Residual settlement requirements: feasible and affordable?" on 27 April 2005. The topic is apparently in the spotlight. In the period after completion of infrastructure and new residential areas, maintenance costs are largely determined by the settlements, and especially differential settlements, that occur after completion. Therefore, strict requirements for these residual settlements are often imposed in contacts, but they substantially increase construction costs. So the question is: how do we arrive at residual settlement requirements that are realistic in the sense that the financial and social inconvenience is contained and that it all remains affordable as well. At the symposium, four speakers addressed the issues; an animated discussion followed at the end based on four propositions that the speakers had posed at the end of their speeches. The symposium took place under the auspices of Delft Cluster, Fugro and KIVI Geotechnics. The abstracts of the presentations can be found on the special symposium page on Geonet. Soon, the speakers' sheets will also be available there so you can read it again afterwards - or for the first time if you were not among the lucky first 130 registrants.
Arjan Grashuis of Rijkswaterstaat DWW opened the quartet of speakers. He emphasised new contract forms as a means of generating technological innovation. In doing so, he did signal the importance of an integral approach, for example when using alternative materials such as eco-granulate. That can cause unexpected, non-geotechnical problems if you want to lay pipes in it later. His contention that innovative contract forms promote innovation was not shared by all in the discussion: contractors have a few methods on the shelf that they will offer coûte que coûte; the way clients throw not only the design but also the risks over the fence; were two of the objections. That anything is better than one prescribed solution and that the modified proposition 'innovative forms of contract promote price/quality optimisation', however, could be agreed upon.
Meindert Van, GeoDelft, gave a cost-benefit analysis of different variants of low-settlement and settlement-free embankments. Besides the reference 'vertical drains'as a standard solution, he distinguished consolidation-accelerating measures such as vacuum consolidation, lightweight solutions with Styrofoam, for example, and the underpinning slab. Broadly speaking, in this order, settlements decrease, as does construction time. In contrast, costs increase. The product of construction time and costs is more or less a constant. Looking more closely, the technique with the most settlement turns out to be the cheapest in financial terms. But actually, you should also include the congestion costs resulting from the extra maintenance. In order to return the fine to the contractor for failing to meet the residual settlement requirement to the queue-driving motorist, the audience launched the creative idea of using the future toll gates for this purpose: In a traffic jam? Cash in! Besides arguing that minimising life cycle costs should therefore focus on the trade-off between residual set-up and construction time, Van also called for 'claiming construction time back from politicians'.
After the break, CROW director Iman Koster presented the CROW publication 'Reliability of settlement forecasts' to chairman of the day Louis de Quelerij. In true geotechnical style, this was not the 1st or 2nd copy but the 'approximately 575th copy, plus or minus X'. De Quelerij stressed the importance of the booklet to make risks transparent and therefore negotiable, and its importance for education.
Hein Jansen of Fugro was the third speaker. He discussed some of the technical aspects of settlement calculation as covered in the CROW publication. He felt that you should actually always include a relief step in a compression test, stressed the importance of a good estimate of the boundary stress ('if you overestimate it you throw too much sand on it causing it to sink even more than you thought'), and emphasised the need to use an isotachen model instead of the traditional Koppejan method when there is a relief step - when removing a pre-load or the end of a vacuum consolidate. The discussion afterwards suggested saving Koppejan by applying it slightly differently (see discussion in Geotechnical 7 (2003) no3, p26). Jansen felt that you should apply the latest insights; a question from the chairman of the day showed that how many of the attendees actually apply the isotachen model was a minority. The audience noted that some missionary work was still needed and that it was very important to do long-term follow-up measurements to obtain experimental information about long-term behaviour. Almost always, measurement is stopped after delivery.
The fourth and final speaker was Chris Dijkstra of Hydronamic/Boskalis on monitoring during implementation: the observational method, 'because that does sound more fancy than pocket checkfits'. He outlined the practical problems of pocket beacons in a work-in-progress and recalled the invariable lack of measurements from the removal of the over-height (and pocket beacons) until after the asphalt has been applied. In his opinion, the combination of a good model - he too preferred isotachen - with field observations were the best tool for risk management. His final proposition was that residual settlement requirements should be better aligned with the constraints from implementation to avoid unrealistic expectations. This did lead to some discussion between clients and contractors in the room, from which quite a conflict model emerged: the contractor just goes to work and if, after a number of years, it turns out that the residual settlement requirement is not being met, then it will be up to the courts to decide who is right, was somewhat the picture. Van Staveren, GeoQ specialist at GeoDelft, urged not to go down that road but to innovate from a common interest, as the technology is apparently not yet far enough along for hard verdicts.