Complete Buying Guide: How to Choose Container Chocks for Any Ground Type

Why Chocking a Shipping Container Is Crucial

A shipping container, whether 20 or 40 feet, is designed to rest on its four corner blocks, standardized structural points (ISO 668). When placed directly on uneven, soft, or sloped ground, loads are poorly distributed: the floor can deform, doors jam, and in extreme cases, the container can tip over. Proper chocking is therefore not just a matter of comfort: it determines the module's longevity and the safety of people using it or working nearby.

Container chocks play a key role in this stability. They distribute the load, compensate for unevenness, and prevent corner blocks from sinking. But not all chocks are equal, and the choice depends closely on the ground type, the load supported, and the duration of installation.

Criteria for Choosing a Container Chock

1. Ground Type and Bearing Capacity

The ground is the first factor to consider. Well-compacted concrete or asphalt offers high bearing capacity: the chock can then be thin and rigid. On gravel, the risk of point sinking increases, and a chock with a wider bearing surface becomes necessary. On dirt or soft ground, it is often necessary to combine a chock with a distribution plate to prevent sinking. The 40 x 26 cm recycled polypropylene chock is designed to adapt to all these cases, but ground preparation remains essential on the most unstable terrain.

2. Load to Be Supported

Each corner of a container does not support the same load. An empty 20-foot container weighs about 2.2 tonnes, but once loaded, it can exceed 30 tonnes. The load per corner depends on load distribution. It is therefore essential to choose a chock whose working load is greater than the actual load per corner, including a safety factor. The chock presented here supports a maximum load of 5.5 tonnes on hard ground, with a recommended working load of 2.1 tonnes and a safety factor of 1.5.

3. Height and Stacking

To compensate for a slight slope or unevenness, stacking is a simple solution. Not all chocks can be stacked stably. An interlocking or flat-surface system allows up to five units to be stacked, providing adjustable height in 4.5 cm increments. This avoids ground excavation and allows precise leveling.

4. Material and Durability

Wood rots, splits, and attracts insects. Concrete is heavy and can crack pavement. Rubber crushes under heavy load. Recycled polypropylene offers a good compromise: rigid, impact-resistant, unaffected by moisture and common chemicals, it does not deform under freeze-thaw cycles. It is also recyclable at end of life.

5. Maintenance and Cleaning Resistance

On a construction site or in a port area, chocks get dirty quickly. A smooth, non-slip surface facilitates cleaning. Resistance to high pressure (200 bar) and temperatures up to 80 °C allows quick maintenance without deterioration.

Comparison of Chocking Solutions

To make an informed choice, here is a comparison table of the main options available on the market.

• Wooden chocks: inexpensive, but sensitive to moisture, insects, and concentrated loads. They rot and must be replaced frequently.
• Concrete chocks: very strong, but heavy, difficult to move, and likely to crack the ground.
• Recycled rubber chocks: grippy and flexible, but they crush under high loads and deform in heat.
• Metal chocks: robust, but rust and can scratch surfaces.
• Recycled polypropylene chocks: lightweight (6.2 kg), rigid, weather-resistant, and chemical-resistant, stackable up to 5 units. They offer an excellent performance/durability ratio.

Which Chock for Which Ground Type?

Concrete and Asphalt

On these hard, flat surfaces, the goal is to prevent punching and distribute the load. A thin, rigid chock is sufficient. The 4.5 cm high polypropylene chock is ideal: it slides under corner blocks without creating overhang and does not scratch the surface.

Gravel

Gravel tends to crush under load points. A chock with a wider bearing surface limits sinking. It may be useful to compact the gravel or add a distribution plate under the chock for heavy loads.

Dirt and Soft Ground

On unstabilized terrain, the risk of sinking is major. The chock alone is not always enough: it is recommended to prepare a base with compacted gravel or distribution plates. The polypropylene chock, with its 40 x 26 cm, offers a good base, but a soil study may be necessary for permanent installations.

How to Determine the Number of Chocks Needed

A standard container rests on four corner blocks. Therefore, at least one chock per corner is needed, i.e., four chocks for a 20 or 40-foot container. For 45-foot containers or special modules, more may be needed or chocks may be doubled under each corner. In case of heavy load or very soft ground, an additional chock per corner can be considered to distribute pressure. The exact number depends on the total load and ground bearing capacity. A professional can help you validate this sizing.

Mistakes to Avoid When Chocking

• Placing the chock anywhere other than under the corner blocks: this creates unforeseen stresses on the floor or walls.
• Neglecting ground preparation: on soft terrain, the chock can sink gradually.
• Using chocks unsuitable for the load: exceeding the working load can cause failure.
• Forgetting to check stability after weather events: heavy rain or freeze-thaw can alter the base.
• Confusing static chocking with transport securing: ground chocks do not replace approved systems for road or sea transport.

Regulations and Best Practices

In France, installing a container for residential or office use may require prior declaration or a building permit depending on surface area and duration. Even for storage use, local urban planning rules should be respected. Regarding transport, the container must be secured in accordance with the Highway Code; ground stabilization chocks are not securing devices. For sea transport, containers are fixed with twist-locks. The chocks presented here are intended for static ground use, in addition to site safety devices.

Sector-Specific Use Cases

Construction and Job Sites

Site welfare units are often installed on unstabilized terrain. A poorly chocked container can deform and make doors and windows difficult to operate. Chocks distribute the load and extend the module's lifespan.

Logistics and Container Yards

In storage yards, containers are sometimes stacked on multiple levels. The first row must be perfectly stable to support the weight of upper containers. Chocks ensure this stability and prevent damage to units.

Events

Containers are often installed on lawns or parking lots. Chocks allow quick leveling of the assembly without excavation, facilitating setup and dismantling.

Agriculture

For storing equipment or crops, chocks prevent corners from sinking into waterlogged soil and limit corrosion from direct contact with ground moisture.

Modular Housing and Offices

A level container is easier to insulate, equip, and connect to utilities. Chocking is an essential step before any fitting out.

Maintenance and Durability

Maintenance of polypropylene chocks is minimal: periodic cleaning with clean water or a pressure washer is sufficient. Avoid aggressive solvents and sharp metal tools. For prolonged storage, stack them away from intense direct sunlight. Visually inspect them before each use to detect any abnormal wear. A cracked or deformed chock must be replaced.

How to Properly Prepare Your Ground Before Installing Chocks

The success of chocking largely depends on ground preparation. On hard, flat ground, a simple sweep to remove gravel and debris is sufficient. On dirt or gravel, it is advisable to lightly excavate, compact the surface, and if necessary, add a 0/20 gravel layer about ten centimeters thick. This preparation helps equalize bearing capacity and prevents chocks from sinking unevenly. For sloped terrain, it is better to create a horizontal platform rather than compensate solely by stacking, as excessive stacking can reduce lateral stability. Finally, check flatness using a spirit level or rotary laser: a few millimeters of deviation affects the entire container and can make doors difficult to operate.

Precise Positioning of Chocks Under Corner Blocks

ISO container corner blocks are cast steel pieces located at the four corners, drilled with standardized holes. They are the only load-bearing points provided by the structure. The chock must be centered under the block, without extending excessively outward to avoid tripping hazards, nor inward to avoid creating overhang under the floor. On a 20-foot container, the distance between blocks is about 5.85 m in length and 2.26 m in width. On a 40-foot, the length is about 11.98 m. These standardized dimensions ensure that the 40 x 26 cm chock remains well positioned under each block. Ground marking or a visual reference can help reproduce positioning during repeated operations.

Adapting Chocking to Stacked Containers

When containers are stacked, the stability of the lower row is critical. Each corner of the upper row transmits its load to the corresponding corner of the lower row via the corner blocks. Chocks placed under the first row must therefore support not only the weight of the bottom container but also that of containers stacked above. It is imperative to verify the total load per corner and ensure it remains below the chock's working load. For stacks of more than two levels, a structural study is recommended. Polypropylene chocks, with their safety factor of 1.5, offer a margin, but do not replace precise calculation.

Impact of Climatic Conditions on Chocking

Temperature and humidity variations influence the behavior of the ground and chocks. During freezing, the ground can swell, creating differential uplift. During thaw, it can soften and lose bearing capacity. Polypropylene chocks resist these cycles without deforming, unlike wood which can split. In coastal areas, salty air can corrode metal parts, but polypropylene remains unaffected. In heavy rain, water can accumulate around chocks and soften clay soil; it is then prudent to check stability and, if needed, add a drainage layer. Inspection after each major weather event is a good habit.

When to Call a Professional

Chocking a container may seem simple, but some situations require expert advice. If the container is to be stacked more than two levels high, if it is intended for residential or office use with significant loads, or if the ground shows signs of instability (subsidence, marshy area, proximity to excavations), a soil study and validation by an engineering firm are recommended. Similarly, for installations subject to planning permission, it is useful to consult the local planning department. Finally, if you have any doubt about the number of chocks or their arrangement, our team can advise you based on your configuration.

Conclusion

Choosing the right container chock depends on ground type, load, installation duration, and maintenance constraints. The 40 x 26 x 4.5 cm recycled polypropylene chock, stackable up to 5 units, offers a versatile and durable solution for most situations. Available exclusively on our site, it comes with a video tutorial for correct installation. For advice on the number of chocks needed or adaptation to your configuration, our team remains at your disposal.