In Portugal groynes are one of the most common shoreline protection structures. This study presents a methodological proposal for the mapping and assessment of the block materials from coastal protection structures, such as groynes. An applied cartography for the armour layer of the Paramos groyne case was first developed in a georeferenced GIS base. Geotechnical and geomechanical parameters, particularly, petrophysical features, weathering grade and uniaxial compressive strength, were then assessed. The results obtained allowed to define a geotechnical zonation for the Paramos armour layer, according to the type of lithology, weathering grade and strength of the rock materials. The methodology developed proved economical and easy of use, providing a geological-geotechnical characterisation valuable to improve the diagnosis of the groynes' status, as well as the monitoring and maintenance of the kind of structures. In addition, it contributes to clarify our understanding of the coastal management of Espinho area.
The shoreline protection against coastal erosion is a complex problem. According to the specific framework, different methods and coastal structures may be used to protect the shoreline. Among the most generalized constructions in use there are the so-called groynes. These are transverse coastal structures, whose function is to retain the littoral sediment transportation, in order to stabilize the beach. Normally they are built in groups and are designated as fields of groynes. These coastal defenceworks may be integrated with longitudinal and adherent constructions, and in some cases, theymay be artificially nourished (e. g., LCPC, 1989; CIRIA/CUR, 1991; USACE, 1995). Due to their characteristics, these structures are designed under the condition that maintenance and repair works will certainly be needed during the structure's life (e.g., USACE, 1990; Silva, 1996; Santos et al., 2003). This study provides a proposal for the geotechnical mapping evaluation of the armour layer block materials in groynes, according to the type of lithology, weathering grade and strength of the rock materials. This is a profitable approach, in the sense that it provides information crucial to extend the average life-time of these coastal protection structures. It also emphasizes the importance, and need, of geotechnical studies for a more efficient planning of this kind of constructions. The cost of the structure, its expected behaviour, aswell as, the consequences of its failure on the groyne's base, do justify the geotechnical site investigations, which will help in the process of decision making concerning the time of maintenance or repair or of works initiation.
The purpose of this study is to demonstrate the importance of coastal geology and engineering concepts for the planning of maritime structures, such as groynes (e. g., Gomes, 1977; LCPC, 1989; CIRIA/CUR, 1991; Mota Oliveira & Martins, 1991; USACE, 2002). The main aim of both the mapping and the systematic inspection of these structures is to define and characterise the natural and artificial blocks constituting the groynes.
