This is a common question for urban planners and community designers. The direct answer is: while it is technically possible to anchor benches into grass or dirt, installing them on a prepared hard surface is almost always recommended for public, permanent installations. Here’s a detailed look at the why and how.
Anchoring a bench directly into grass or soft earth presents significant challenges. The primary issue is stability. Soil shifts with moisture—expanding when wet and contracting when dry. This movement can cause the bench to rock, tilt, or become uneven over time. In grassy areas, regular mowing and foot traffic around the legs can erode the soil, further compromising stability. Furthermore, anchoring into dirt often requires longer, more substantial ground anchors or concrete footings below the frost line to prevent heaving in colder climates, which involves excavation similar to creating a hard surface pad.
For these reasons, a hard surface—such as concrete, asphalt, or compacted gravel over a sub-base—is the superior choice. A concrete pad provides a stable, level, and permanent foundation. It prevents the legs from sinking, minimizes weed growth around the bench, and defines the seating area clearly. For installations where a natural look is desired, permeable options like pavers set on a gravel base or reinforced turf systems can offer a compromise, providing stability while allowing grass to grow through.
The installation method is also crucial. Benches on hard surfaces are typically secured using concrete anchor bolts or heavy-duty surface plates. If anchoring into soil is absolutely necessary (for a temporary event or in a highly naturalized park area), specialized helical earth anchors or concrete-filled post holes dug below the frost line are required. However, this "soft surface" installation often ends up being more labor-intensive and less durable than a simple concrete pad.
In summary, for long-lasting, safe, and low-maintenance urban benches, a prepared hard surface foundation is the standard and advised practice. It ensures the bench remains securely in place for years, accommodating daily public use. While anchoring into dirt is feasible with significant engineering effort, the practical benefits of a solid base make it the preferred solution for most municipal and commercial projects.