Ground-penetrating radar survey to detect sub-slab voids beneath the East Promenade at Rhyl

At Rhyl, a tourist resort on the North Wales coast, the East Promenade is s usceptible to damage by marine scouring processes. Concealed scour cavities were suspected following the sudden collapse of a segment of the promenade and the recognition of numerous depressions and zones of cracking elsewher e in the concrete pavement. The full threat posed to the integrity of the p romenade and to the safety of pedestrians remained uncertain and costly rec onstruction was anticipated. Ground-penetrating radar was used along a 260 m stretch of the promenade to determine the full extent of voiding beneath the surface. The geophysical survey delineated the known cavity and, contra ry to expectations, demonstrated that the sub-slab voiding beneath the rema inder of the promenade was relatively minor. The more subdued radar feature s encountered were interpreted as minor separation beneath slabs due to con solidation. The results provided a basis for design and construction of eff ective and inexpensive repairs to the promenade foundations that ensured th e public safety.