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Timber crib wall failure and repair solutions

How to repair a failed retaining wall

Retaining wall failure, timber crib wall failure, and retaining wall repair are all covered in this article.

Timber criblock walls have an agreement certificate showing a sixty-year lifetime, but the life span depends on the quality of the timber treatment, stone fill, and workmanship.

The main cause of the failure of timber crib walls is rotten timber headers that go from the front to the back of the crib frames.

The main causes of failure are:

Poor-quality timber
Poor-quality timber treatment
Poor-quality stone fill
No or blocked rear wall drainage
Poor installation

The main cause of the rot is poor infill stone that is full of fines. The material stays damp.

We have many examples of timber criblock walls failing within twelve years of construction.

Examples of timber crib wall failure:

(Top-of-wall failure)

(Bottom-of-wall failure)

How can you repair a damaged timber crib wall?

Once the timber begins to rot, you can make local repairs by replacing the front stretcher. In time the timber inside the wall will rot, and this is not accessible. You will be wasting time and money carrying out repairs.

Methods to permanently repair the retaining wall.

1) Demolish the existing wall and replace it with a concrete or eco-crib wall. (eco-crib made from recycled plastic) or other types of retaining wall for example, gabion, segmental blocks. Take a look at the price comparison page to see the cost of each type.

2) Leave the existing wall in place, soil nail a galvanised steel mesh to the face of the timber crib, then lay earthbags on the face, and finally hydroseed the surface of the earthbags to grow a grass bank.

3) Leave the existing wall in place and lean a gabion basket retaining wall against it. Design the gabion wall as if the criblock had failed, as this would be the case in time. This solution works if there is space in front of the existing wall. Depending on the height of the wall, 1m to 2m of space will be required.

4) Leave the existing wall in place and build a king post retaining wall in front of it. Design the king post retaining wall as if the criblock had failed as above. A king post wall solution is perfect when space is a premium, as the wall only takes up 200/300mm.

A site investigation borehole would be required to ensure the soil is suitable for a king post wall. Any rock within the embedment depth would not allow this method to work.

5) Leave the existing wall in place, and strengthen it using soil nails. The soil nails are designed to form a reinforced block of soil, and the reinforced block becomes the retaining structure.

Soil nails have a working life of fifty years, depending on the soil condition and rate of sacrificial corrosion.

A strong galvanised mesh is placed over the surface of the damaged retaining wall. The mesh is held in place with steel plates and bolded to the soil nails.

On completion of the soil nailing reinforcement, the wall can be cladded with a gabion basket, segmental or masonry wall.

How much will it cost to replace a crib wall?

Option 1) To demolish the existing wall and replace it with a concrete or eco-crib wall between £750/£950 m2 depending on the height of the wall, and access

Option 2) soil nail a galvanised steel mesh to the face of the wall, install earthbags and hydorsee. Soil nailing only – ££175/£375 m2. With earthbags £375/£575 m2. Price depends on wall height, access and scale of project.

Option 3) To build a gabion basket retaining wall in front of the existing failed wall between £350/£550 m2, depending on the height of the wall, and access, subject to design.

Option 4) To build a king post retaining wall in front of the existing failed wall between £450/£700 m2, depending on the wall height and access.

Option 5) To reinforce the existing wall using a strong galvanised steel mess, anchored using soil nails between £175/£375 m2. To then cover the area with a Reno Mattress (gabion) filled with stone £400/£600 m2.