The ERFA system pursues the notion of part protection with the aim of reducing the risk of sinkholes and the associated costs to an acceptable level through cost-effective and simple action. Here, in the case of an event the system may deform to the extent that a sinkhole is visually perceptible whilst not endangering road users. Compared to a rigid structure, it can then react promptly to prevent a progressive breaking away of the subsoil.
The sinkhole protection system consists of standard reinforcement steel strands functioning as linear bearing elements and a high-tensile, diamond-shaped steel wire mesh functioning as a flat force spreading element.
When using the ERFA system, the thickness of the spoil plus the combined binder and top layers is relatively small compared with the sinkhole diameter. As a result no load bearing arch can form. Corresponding to the break-in model the total applied load is to be carried through the membrane. The resulting forces are to be transferred laterally in the road longitudinal axis. The ERFA system possesses pronounced anisotropic characteristics and as a result can be dimensioned for the level case according to the membrane theory.
To verify the functional suitability of the ERFA system, full-scale 1:1 field tests were carried out. Placed first was an asphalt load bearing layer and secondly a concrete slab with thickness of 20 cm and width of 2.5 m. The modeled sinkhole exhibited a rectangular hollow with a free span width of 3.0 m. A total loading of 30.4 tons resulted in a depression in the slab center of approx. 20 cm. The ERFA system showed considerable reserves to be available.