The maintenance costs of Dutch infrastructure amount to many billions every year. These costs are largely determined by residual settlements. These are the settlements that occur after the project is completed. Underpinning must compensate for unevenness of the track. Additional overlaying with asphalt is needed to eliminate erosion. Ten years after completion of the VINEX district, pipes and sewers are already in need of repair.
Contracts therefore set strict requirements for residual settlement. However, requirements that are too strict unnecessarily increase construction costs. Especially when the construction time has to be reduced in the meantime. So the question is: which residual settlement requirements are feasible and affordable?
On 27 April 2005, the afternoon symposium "Residual settlement requirements: feasible and affordable?" sought answers in the form of four lectures followed by panel discussions. The lectures featured the client, the contractor, the consultant and the researcher. They discussed contract requirements, execution techniques, residual settlement prognoses and measurements. An impression of the meeting can be found here.
The symposium is part of the knowledge dissemination activities of Delft Cluster, low-maintenance infrastructure project.
General information on the phenomenon of compression (settlement), and more specifically on the isotope model, can be found in the Dossiers - Soil Deformation section.
Presentations
Towards innovative residual settlement requirements
Limiting residual settlements is an important goal in infrastructure design in the Netherlands. Contract forms are changing and with them residual settlement requirements. Absolute residual settlement requirements are being replaced by functional requirements on, for example, flatness. The question is how far this development should and can go. It depends on how the functional requirements can be tested. And on the possibilities and limitations provided by the geotechnical design in this respect.
Costs and benefits of settlement accelerating / low settlement techniques
Dr Ir Meindert Van, GeoDelft
Traditional embankment of sand is often not the most economical. Residual settlement and the resulting maintenance costs can be reduced by settlement-reducing or settlement-accelerating techniques. An overview of these techniques and lightweight materials is given. The performance of the various techniques in terms of total settlement, residual settlement, construction stability, construction time, maintenance, space requirements, future extensions, dynamic behaviour, crossing pipes, experience and, of course, costs is indicated. The performance of the various techniques is illustrated on the basis of practical situations.
Reliability of settlement forecasts
Iman Koster presents the publication Reliability of settlement forecasts on behalf of CROW and hands it to Prof Louis de Quelerij.
The influence of the consultant
Ir. Hein Jansen, Fugro
Consultants have great influence on the reliability of settlement forecasts. That is the conclusion from a comparative study in CROW publication Reliability of settlement forecasts. Especially design liberties appear to play a major role. A scoring table showing the effect of error sources is now available via the ZETFOUT programme. With this table, it is possible to quickly determine by which effort the reliability can be increased the most.
Extrapolating the settlement line measured during execution requires a reliable calculation model. For current embankment methods with temporary preloading, the traditional Koppejan model appears to perform inadequately. However, even with better measurement and calculation methods, a risk will always remain.
Risk management through monitoring
Ir. Chris Dykstra, Hydronamic/Boskalis
Working with soil means that there is always a risk of reality deviating significantly from the design. Deviations may occur because the soil structure is different or because of shortcomings in the settlement models used. The actual behaviour is determined by measuring settlement and possibly pore pressure. With the measured settlements, an adjusted prognosis of residual settlement can be made. The possible need to take additional measures (e.g. more over height) then also becomes apparent. Monitoring plans and forecasts based on pocket fissures are explained using practical examples. Preconditions and limitations are also discussed.
Panel discussion
Discussion leader: Prof Louis de Quelerij, Delft University of Technology.