Finding a large tunnel appearing under a garden shed — especially one that keeps reappearing even after you fill it in — can be unsettling and frustrating. Not only is it a mystery to solve, but it’s also a serious structural concern. If an animal is continuously digging beneath a concrete slab, the foundation of the shed could weaken and eventually crack. Preventing that damage and identifying what’s causing the digging are the first priorities.
In this guide, we’ll explore the likely causes of persistent digging under sheds, what kinds of animals are usually responsible, why conventional fill-and-pack methods often fail, and what steps you can take to stop the digging and protect your shed’s foundation long term.
What Kind of Animal Might Be Making the Tunnel?
When you see a large tunnel under a structure, several animals could be responsible. The size of the opening, the soil type, the local environment, and evidence like tracks or droppings can help narrow down the culprit. Some of the most common diggers include:
1. Groundhogs (Woodchucks)
Groundhogs are classic tunnel builders. They dig large burrows with multiple entrances, often hidden around foundations, decks, or sheds. Their tunnels can extend several feet underground and pose serious risks to structures.
Signs of groundhogs:
Large holes (4–8 inches wide)
Loose soil piled near the entrance
Nearby grassy or garden areas with missing plants
2. Rabbits
Rabbits sometimes dig shallow burrows, particularly in soft soil, but they are less likely to create deep concrete-undermining tunnels unless vegetation is dense and shelter is nearby.
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