DIKE ENGINEERING - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 303

a combination of these three criteria is taken as the target reliability. This approach
is still a subject of national debate.
Functional analysis
The basic function of a dike is to retain the water. Various elements can be
distinguished each playing a characteristic role in the functioning of the dike.
These principal elements are (see Fig 17.6)
- The crest height should be above the design water level.
- Outer slope: a watertight cover in order to keep the inner groundwater table and
leakage low and resistant against rapid draw down, ice and earthquake.
- The core of the dike conveys the horizontal load due to the water to the subsoil.
- Inner slope: a permeable cover to keep groundwater table and leakage low and
stable under overtopping and earthquake.
- The subsoil provides suitable stability and has a water retaining function.
In urban areas existing buildings in and on the dike can jeopardise its function. The
watertight cover is locally interrupted, differential settlements can cause cracks and
maintenance becomes more complicated. Using functional analysis two principal
solutions can be defined for the situation of buildings on a dike: fully integrated,
when the buildings and their foundations are also the water retaining structure or
building and dike are functionally separated. This can be achieved by various
measures. In these solutions the effects on the elements of the dike must be
considered precisely and in detail (leakage, stability, erosion, etc.). For trees, cables
and pipelines on and in the dike the same holds. They are admitted when they do
not interfere with the principal dike function (separation and evaluation of
functions). If the problems related to buildings and trees can be solved in a
technical way, the question of control and maintenance is to be solved. When the
water retaining function and building are fully integrated, frequent inspection is
necessary. Uncontrolled changes in the buildings by their owners may be a danger
to the dike function and a threat to the safety. It is recommended to plan the design
for a period of 100 year. If buildings are outside the technical dike profile the
inspection is more complicated, particularly when the fundamental elements
(watertight screen) are not directly visible. The quality can be checked by adequate
measurements during high waters. For buildings in the lee-side area a regular
inspection of the cellars and the maintenance of the lee-side slope is required. The
present-day development of houses in the river forelands, although officially
prohibited, became lucrative and popular, but it raises a serious new political issue,
as safety is at stake during high river discharges.
Dike maintenance
The technical component of management is daily maintenance, which consists of
inspection, taking measures and allocation of personnel, materials and equipment.
The condition of a water-defence system will degenerate in the course of time.
Moreover, the loading conditions may change, and new insight in the evaluation of
strength of elements in the system may arise. Two fundamental activities, periodic
inspection and taking measures in time, form the backbone of a proper
maintenance policy. Periodic inspection implies a comparison between actual