A crib wall is a gravity retaining structure assembled from interlocking precast concrete or timber units stacked to form a lattice of open cells, which are then filled with free-draining granular material. The mass of the filled crib, not the units themselves, resists the earth pressure behind the wall. Crib walls are used on highway cuttings and embankments, site level changes and landscaped terraces where a fast, drained and plantable face is wanted.
How a crib wall carries load
The units are laid as alternating headers and stretchers, so the assembled wall forms a series of connected boxes. Once filled and compacted, the wall behaves as a gravity mass structure: overturning, sliding and bearing are checked in the same way as for a mass concrete or gabion wall, to Eurocode 7 and BS 8002 practice. The units themselves are lightly reinforced and are designed to transfer the fill pressure rather than to span. Because the mass depends on the fill, compaction of the cells in layers is a structural operation, not a tidying-up exercise, and the specification should say so.
Concrete and timber crib units
Precast concrete cribs are the standard for highway and infrastructure work. They offer a predictable design life, resist fire and vandalism, and are available in profiles that produce either an open plantable face or a closed face. Timber cribs, historically the original form, remain in use on landscape and forestry schemes where appearance and carbon are the priorities; the design life is governed by the durability class and treatment of the timber, and the assumption should be that the structure will be replaced rather than maintained indefinitely.
Batter, height limits and drainage
Crib walls are almost always built with a batter — commonly between 1:4 and 1:6 — which increases stability and allows the face to be planted. Single-depth cribs are practical to around 3 to 4 metres; above that the wall is built as a double or multiple-depth crib, or the section is stepped, and the design quickly becomes competitive with a reinforced soil structure. Drainage behind and through the wall is inherent to the type: the granular fill and open joints mean water is not able to build up as hydrostatic pressure, which is one of the main advantages over a solid gravity wall, provided the retained fill behind the crib is itself drained to an outlet.
Crib wall, gabion wall or reinforced soil
All three are gravity or gravity-derived solutions with a permeable face. A gabion wall is more tolerant of differential settlement and easier to build to an irregular alignment, and it accepts a wider range of fill stone. A crib wall gives a more regular architectural face and a shallower footprint for the same height. Reinforced soil — geogrid layers within the retained fill behind a facing — becomes the economic choice as heights rise past roughly 4 to 5 metres, because the required mass no longer has to be provided by the structure itself.
Related ViaCon solutions
ViaCon supplies gabion, geogrid and reinforced soil systems for retaining structures. See our geotechnical solutions range. Related glossary entries: retaining wall, gabion, geogrid and soil stabilisation.
Frequently asked questions about crib wall
What is a crib wall?
A crib wall is a gravity retaining wall built from interlocking precast concrete or timber units stacked into open cells that are filled with free-draining granular material. The mass of the filled crib resists the earth pressure behind it.
How high can a crib wall be built?
Single-depth crib walls are typically practical to around 3 to 4 metres. Greater heights require double or multiple-depth cribs, a stepped section, or a switch to a reinforced soil structure.
Do crib walls need drainage?
The granular fill and open joints mean water can pass through the wall rather than building up behind it, which is one of the main advantages of the type. The retained fill behind the crib still needs to be drained to a positive outlet.
Crib wall or gabion wall — which is better?
A gabion wall tolerates differential settlement better and suits irregular alignments; a crib wall gives a more regular face and a slightly shallower footprint for the same height. Both are gravity structures with a permeable, plantable face.