Flexible (Unbound) Paving System

Unbound paving works through friction and confinement. Separate units sit in a thin loose bedding layer, the gaps between them are packed with granular material that lets neighbouring units share what lands on them, and the whole field is closed at its perimeter by a restraint that is not supposed to move. Nothing is stuck to anything else, and that is the intention rather than a shortcoming.

The nearest sibling is the rigid paving system, and the test can be carried out by hand on site: try to lift one unit. Here it comes out, because it was only bedded and confined, and it goes back into the same space. In rigid paving the unit is mortared to a bound base and removing it destroys both the unit and the bed beneath. That single difference governs how the surface is repaired, how buried services are reached, and how the construction answers movement in the ground.

Interlock is the usual word for what holds the field together, and no paver possesses it. It is produced by the shape of the units, by the material packed into the joints and by the restraint that stops the field creeping outward. A stack of pavers on a pallet has none of it; the same units laid, filled and confined have all of it.

Because nothing is bonded, the assembly absorbs small ground movements by distributing them across many joints instead of concentrating them into one fracture. The price of that tolerance is a dependence on the joints staying filled and the restraint staying put, which makes upkeep a structural matter here rather than a cosmetic one.

Load arriving on one unit does not stay there. It passes through the filled joint into the units around it, so a group works together and the pressure reaching the bedding is spread across more area than the unit actually loaded. Empty a joint and that path vanishes: the unit rocks, the bedding beneath it is worked loose, and its neighbours begin receiving the same treatment.

The restraint and the joints are two halves of a single mechanism. Confinement keeps joints tight enough to transfer load, and load transfer keeps the field behaving as a field rather than as a crowd of independent units. Where a restraint drifts outward, joints open, filling escapes, transfer weakens and the field spreads a little further, a sequence that feeds itself and does not stop unaided.

The laying course sits between two things it cannot govern. Above it, units press down wherever they are loaded; below it, a sub-base surface that is not flat forces the loose material to be deeper in some places than others. Deeper bedding compresses more, so an irregular foundation prints itself into the finished surface after traffic arrives rather than before it, which is why a newly laid surface can look faultless and a used one can look tired.

Water ties the whole thing together. Joint filling that stays put keeps most rainfall on the surface; filling that has been washed or blown away lets water into the bedding, and saturated bedding pumps up through the joints under wheel loads, carrying more filling out with it. The visible symptom is a depression ringed by clean, empty joints, and the cause is a drainage and confinement problem wearing the appearance of a paver problem.