Designing urban landscapes that successfully support both healthy tree growth and the structural demands of pavements, pathways, and vehicular areas is a complex engineering challenge.
Beneath the surface, the soil cell system plays an essential role in meeting these demands. Its ability to bear static loads, resist lateral forces, and preserve large volumes of uncompacted soil depends on whether it is installed as a fully interlocking, gap-free structure.
When soil cells are properly connected, the system behaves as a single, continuous structural module. When they are spaced apart, the system’s behaviour changes dramatically, becoming unpredictable, weakened, and difficult to model with confidence. This single installation decision can determine whether the landscape above performs reliably for decades or becomes a liability.
Why Gaps Between Soil Cells Undermine Structural Integrity
Spacing soil cells apart — whether to reduce costs or simplify installation — may appear harmless, but it can undermine the performance of the entire system. Even small gaps interrupt the interlocking pattern the cells rely on to achieve strength and rigidity.
Once gaps exist, the system is no longer acting as the engineered product that has been tested and modeled. Instead, it becomes an untested configuration with unknown performance characteristics. This introduces a series of structural risks, especially in areas exposed to vehicle loading.
Gaps weaken the system in several ways:
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Reduced static load-bearing capacity: The cells can no longer distribute vertical loads across the network, creating weak points susceptible to deformation.
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Loss of lateral rigidity: With the interlock broken, the system flexes and shifts under pressure, increasing strain on pavements.
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Unpredictable performance: Engineering calculations become unreliable because the installation no longer matches the tested configuration.
In paved areas subject to vehicle use, this can result in subsidence, rutting, or pavement failure. In high-profile urban landscapes, these outcomes are not only expensive to repair but often highly visible.
The Concrete Slab Problem: When “Fixing” Gaps Makes Things Worse
There is sometimes a belief that geotextile can compensate for spacing. While geotextile is excellent for soil containment and separation, it has no structural capacity. It does nothing to restore the missing rigidity between spaced soil cells.
To genuinely bridge gaps, the only viable solution is often to install a concrete slab across them. However, this creates its own set of challenges:
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Higher carbon footprint
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Greater installation complexity
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Increased cost
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Reduced soil volume and permeability
In effect, spacing soil cells often forces designers to introduce additional hardscape, undermining the environmental benefits the system is intended to deliver.
Interlocking Systems: The Only Reliable Way to Maximize Performance
High-quality soil cells are designed and modeled as interlocking, continuous structures. Their performance depends on this interconnection. When assembled without gaps, the system provides:
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Predictable static load-bearing behaviour
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Reliable lateral strength under traffic loads
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Even distribution of vertical and horizontal forces
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A stable environment that prevents pavement heave
Just as importantly, interconnected systems create and maintain large volumes of uncompacted soil — critical for root expansion, aeration, and water movement. Without this soil quality, urban trees cannot thrive or reach maturity. Gaps not only weaken the structure but also disrupt soil continuity, fragmenting the growing environment the system was designed to protect.
Why Lattice Systems Outperform Column-Based Designs
The internal geometry of the soil cell system plays a significant role in its ability to resist pressure and maintain its shape. Lattice-style systems with infill panels offer key advantages over column-based systems, particularly under lateral load.
Lattice systems provide:
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Superior lateral strength, due to continuous cross-linked support members
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Improved backfill confinement, reducing soil migration and settlement
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Greater open soil volume, allowing trees to develop stronger, deeper root systems
Column-based designs may offer vertical support, but they lack this horizontal cohesion. Under the pressure of traffic loads or soil movement, they are more prone to deformation and offer less protection against backfill loss.
RootSpace®: A Seamless, Gap-Free Structural Environment
RootSpace exemplifies the principles required for modern, high-performance soil cell systems. Its tightly connected lattice structure forms a seamless, rigid environment without the weak points created by gaps. By eliminating spacing, RootSpace maximizes both structural performance and soil volume.
This approach delivers several benefits:
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A continuous underground structure with high static load capacity
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Exceptional lateral loading performance, ideal for vehicular areas
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Consistent, uncompacted soil volume across the entire system
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Stable pavements that resist heave, settlement, and deformation
By functioning as a single, unified module, RootSpace supports both the engineering requirements of the surface and the biological needs of the tree.
The Bottom Line: Interlocking Is Not Optional
Urban tree planting is a long-term investment. The performance of the soil cell system beneath the pavement determines whether this investment thrives or fails. Interlocking soil cells ensure predictable engineering behaviour, long-term pavement stability, and healthy, mature trees.
Spacing soil cells introduces unknown variables, weakens the structure, and undermines the environmental intent of the design — often requiring more concrete and additional cost to compensate.
The solution is straightforward: install soil cells exactly as they were engineered — interlocked, gap-free, and structurally continuous. This is the only reliable way to ensure both pavement safety and thriving urban tree growth for decades to come.
