Engineering properties of marine sediments in Mali Ston Bay (Croatia) based on “Mainland-Pelješac” bridge investigations

The complete geological characteristics of the wider area of the Pelješac peninsula are presented: lithostratigraphical, structural/tectonic and seismotectonic. The main accent is put on engineering geological characteristics of clastic sediments in Mali Ston Bay encountered during investigations for implementation project of the “Mainland-Pelješac” bridge. The bridge large proportions with 2404 m in length and with 14 pylons under the sea, requested thorough and expensive in-situ and laboratory investigations which enabled development of detailed and reliable engineering model of quaternary clastic sediments at the explored site. The results clearly indicate three different engineering units which are predominantly classified according to the obvious difference in consistency: Unit A – very soft and soft soil; Unit B – soft to firm soil and Unit C – firm soil. Because of great soil total thickness, locally over 100 m, its generally poor engineering properties and great seismicity of the area the foundation surroundings are unfavorable. The mentioned units which are classified according to its engineering properties also tightly correspond to the deposition environments which represent much wider area than just exploration site. Therefore authors presume presence of units A, B and C in wider area with similar geological situations like proximities of the Zrmanja, Krka, and Cetina deltas.