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How to build a flood wall to protect your property

Flood Wall Construction

Flood wall construction and how to build a flood wall. This article provides a step-by-step guide on constructing a flood defence wall. Flood defences are becoming more relevant as the UK’s climate becomes warmer and wetter.

The flood wall we are going to use in the example has been designed for sandy soil. The flood water will be held back by the wall, but it will slowly seep under the wall and need to be pumped out. The design is different when the flood wall is used in clay soils.

Before the flood wall can be constructed, a structural engineer needs to design it to determine the geometry, foundation size, and correct steel reinforcement specification.

Step 1 – How to build a flood wall excavation

Excavate the foundation to the design profile. Excavate working space to allow formwork to be installed on the sides of the foundation. If the soil is suitable, the foundation can be poured against it, but this solution is not as accurate when formwork is used, as creating a flat and level surface can be challenging.

After the excavation is completed, a 50mm blinding bed of lean-mix concrete is laid to form a working platform. The concrete bed will keep the area clean in wet weather and provide a better surface on which to place spacers for the steel reinforcement cover.

Step 2 – Formwork and steelwork

Install the formwork to the side of the foundation. Place the steel reinforcement to the downstand and foundation, making sure there is concrete cover as specified by the engineer’s design. The cover can be controlled using concrete cover blocks to the bottom, side reinforcement, and circular steel spaces to separate the fabric reinforcement layers.

Finally, install the starter bars. The lower leg of the starter bar is tied to the bottom layer of fabric reinforcement. The centres for the starter bars are 200mm for 200 mm-wide Stepoc blocks and 133 mm for 256 mm-wide Stepoc blocks.

Step 3 – Concrete

When the steel reinforcement is completed, ensure no contaminants have fallen into the foundation. Use the concrete mix the engineer has specified. A concrete pump can be used to pour the concrete. If a concrete pump is being used, make sure the mix has been adjusted, as it will need to have a high slump.

Finish off the concrete surface to ensure it is flat and relatively smooth. A tamp finish is fine.

Step 4 – How to build a flood wall first course of blocks

The first layer of blocks is laid on a wet bed of mortar. A block is set at one end and another at the other end of the wall. A line is then set up, and the blocks are laid to ensure they are flat and level.

Step 5 – Completing the wall

The wall is now built dry. After the second course, the remaining steel bars are tied to the started bars for continuation. Horizontal bars are laid inside the blocks in the formed grooves. Complete the wall to full height. If the wall is more than eight courses high for the 200mm wide Stepoc block, stop at eight courses and concrete the core. The wall becomes unstable for concrete after eight courses.

Step 6 – Concrete core

When the wall is complete, the core can be concreted using the specified mix. A concrete pump can be used to pour the concrete. If a concrete pump is being used, make sure the mix has been adjusted, as it will need to have a high slump.

Step 7 – Drain and filling

The final step is to install the drain and back fill the excavation. Lay the drain as indicated on the design drawings. The drain needs to be installed at least 600mm below ground. Surround the drainage trench with terran 1000 to stop soil fines clogging up the clean stone. Installed a 150mm perforated land drain and cover it full height with 50mm clean stone. The top 150mm can be 20mm of clean stone or gravel.

Connect the drain pipe to a sump chamber fitted with a sump pump. The size of the sump chamber and pumps will be determined by the flow of water through the soil.

Note
Every flood wall we design is different due to the soil conditions and the height of the flood water. If you need support designing your flood wall, tell us about your project below.