Dynamic response of a rocky cliff under the sea wave pulse: a study along the Adriatic coast of Polignano (Apulia, Italy)

The dynamic behavior of a rocky cliff under severe sea waves has been analyzed in the location of Polignano, facing on the Adriatic coast of Apulia, Southern Italy. In this area, the classical and, at the same time, complex problem of the stability of a cliff in calcareous rocks is burdened by the presence on the top of the cliff of the ancient town. To analyze the behavior of the cliff under the impulsive transfer of energy generated by the sea waves, two types of measures were carried out on the rocky mass: (1) ambient noise and (2) strong-motion records. The first type of measures, which may be executed in a short time with a high spatial density, has provided a recognition of the intrinsic and anisotropic dynamic behavior of the coastal cliff. The accelerometric records, carried out during heavy storms in December 2009 and January 2010, allowed to evaluate the energy transfer from waves to cliff, in terms of maximum values and temporal and directional distribution. To facilitate a correct interpretation of the measures, also a geomechanical characterization of the rocky mass has been carried out through the Rock Mass Rating system Bieniawski (The Geomechanics Classification in Rock Engineering Applications. Proceedings of the 4th ISRM Cong., Montreux, pp 51–58, 1979), Bieniawski (Engineering Rock Mass Classifications. Wiley, New York, p 251,1989) and the Markland’s test (A useful technique for estimating the stability of rock slopes when the rigid wedge sliding type of failure is expected, pp 10,1972). The first allowed to classify the rocky masses in terms of quality, the second one to individuate the potential failure mechanisms of the cliff.