During high water levels, seepage water can flow under or through a dyke, quay or flood defence to ground level. In some cases, this water carries sand with it. These so-called sand-carrying seepage wells are an important warning sign, because sand transport can lead to internal erosion and weakening of the flood defence.

Casing is a tried and tested measure for allowing a controlled outflow, allowing sand to settle and enabling the situation to be observed and assessed safely.

Why caskets may be necessary

Sand-carrying seepage often occurs during periods of high water, when the groundwater pressure beneath a flood defence increases. The upward flow can carry sand, indicating a risk of piping.

Boxing is used to slow down the flow, reduce sand transport and limit damage to the ground level and flood defences. It also makes it possible to monitor the development of the well and gain time for additional measures.

Flexible drip tray from Buitink Technology

Buitink Technology has developed a flexible, lightweight alternative to traditional cofferdams made of wooden structures and large quantities of sandbags. The system consists of a teardrop-shaped flexible reservoir with an opening in the bottom and a floating edge.

The design enables rapid installation and is suitable for temporary use in emergencies and flood situations.

Technical operation

After installation over or around the well, the seepage water flows into the reservoir through the opening in the bottom. The system fills automatically due to the presence of seepage flow.

As the water level in the reservoir rises, the weight increases and the cofferdam becomes more stable. The weight of the water provides natural anchoring at ground level, similar to the principle of flexible flood defences.

The floating edge forms a stable barrier against the ground level and prevents uncontrolled outflow.

Image: Flexible cofferdam in unfolded state around a seepage

When is casketing useful or necessary?

Coffining is used in situations such as:

• Cloudy seepage water or visible sand deposits
• Increase in seepage flow or the emergence of new wells
• A 'boiling' effect or active sand transport
• Need for calm in the flow to allow sand to settle
• Need to limit damage and gain time for analysis

By carefully controlling the framing, seepage water is prevented from flowing freely across the ground level and continuously carrying away material.

Advantages of the flexible casing system

• Quickly deployable without heavy equipment
• Self-filling due to the presence of seepage water
• Increased stability due to water weight
• Limited logistics compared to sandbags and timber
• Gentle flow allowing sand to settle
• Reusable after cleaning and inspection
• Available in customised sizes for different situations

Image: Step-by-step plan for rolling out and installing flexible cofferdam in case of seepage

Practical application

The deployment will proceed as follows:

• Placing the reservoir over or around the well
• Automatic inflow of seepage water through the bottom opening
• Stabilisation through increasing water weight
• Monitoring of clarity, sand production and behaviour of the well

If necessary, the system can be combined with additional measures or drainage, in accordance with the applicable emergency or flood protocol.

Customisation and designs

The flexible formwork is available in various diameters, heights and volumes. Depending on the application, the following options are available, among others:

• Overflow or controlled drainage
• Reinforced zones for soft or rough surfaces
• Lifting and handling straps
• Level markings and measuring points
• Transport and storage bag with repair kit

Sample implementation

Image: Flexible formwork with a diameter of 3000 mm and a height of 1000 mm

FAQs