Spectacular river embankment failure accurately predicted

Although river embankments in the Netherlands exist for almost one millenium, much uncertainty about their strength and stability remains.

At the end of 2001 therefore a full-scale test was carried out by GeoDelft and other parties. The aim of the test was to enforce uplift failure of an old embankment along the river Nederlek. Uplift means floatation of impermeable clay and peat layers by excess water pressures in the underlying sand layer. This uplift has also been predicted with the Delft Systems program MStab.

	Water was pumped into sand layers, to simulate the natural excess pressures during high water levels.  At failure stage a large soil mass (width 125m, thickness 17m) started sliding downwards
	It proved that MStab's unique Uplift Van model could predict the actual failure very quickly and accurately.  MStab indicates when reinforcement is really required and therefore allows more cost-effective maintenance.

Maeslant Barrier

After the flooding distaster in 1953 it was clear that the Netherlands needed better protection agains high water levels. Under the so-called "Delta act", therefore huge dike reinforcements were executed and a number of impressive barriers was build. The Maeslant storm surge barrier in the Nieuwe Waterweg has been the most recent one.

The Nieuwe Waterweg is the entrance to the world largest harbor of Rotterdam. The Maeslant barrier consists of two movable cylindrical doors, that will close only during extremely high water levels. The barrier reduces the chance of exceeding the maximally allowed water level from once every 100 years to once every 10,000 years on average. Therefore the required embankment reinforcement along the rivers could be reduced drastically. See also the dedicated Maeslant pages by the Ministry of Transport and Public Works. 

Sobek as part of the decision and support system
The decision as to whether or not to close the Storm Surge Barrier is made by a computer programme known as the Decision and Support System (BOS). Part of that system is the Delft Systems component Sobek.On the basis of a large number of data, Sobek calculates the anticipated water levels at different cities. Apart from current information Sobek also works with historical data (going back 12 days).

Efficiency gain by automated embankment stability analysis

By regulation, the safety of Dutch river embankments must be assessed each five years. Such an assessment was executed  in 2002/2003  for the area "Noord-Holland". The assessment involves the geometry definition and stability analysis of thousands of crosssections, followed by an inspection to find the critical parts. The assigned project engineer states: "This job would not be possible without the automated geometry generation and analysis by MGeoBase. It saved me lot's of time and allowed me to concentrate on the results instead of the labor".  

MGeoBase reads surface descriptions from the existing Geografical Information System, and combines them with probabilities of different soil profiles in order to generate different geometrical cross sections. One button click is then sufficient to start the stability analysis of all cross-sections. Each stability analysis is performed by the integrated MStab program. The critical cross-section results are found simply by browsing directly from MGeoBase. The probability of failure has also been visualized on top-view maps, in order to give a quick impression of the critical parts.

All relevant data has been stored implicitely in MGeobase's database. This means that the next assessment can be executed even more efficiently, because it only takes the modification of changed loads and properties in order to start the re-analysis and re-interpretation. The systems also allows a quick safety scan during measured high water levels.