The geotechnical properties of the sediment body in the estuary of the Rasa River, Croatia

摘要

The RaSa River valley and its estuary are located on the eastern part of Istrian peninsula (north-eastern coast of the Adriatic Sea). Intensive sedimentation in microtidal estuary environment started due to a lowering of sea level during the Holocene. Most of the sediments were brought over by erosion of Paleogene flysch rock mass on the uperstream catchments area and Quaternary deposits from the ancient Cepic Lake. Slow sea level rise during the last 6.000 years created the conditions for filling the earlier formed karstic estuary. Because of intensive sedimentation the mouth of the RaSa River was shifted for approximately 4 km in the last 240 years. The sediment body has uniform granulometric composition, where silt and clay material prevails. The process of consolidation by gravitational compaction is not finished yet. Liquid consistency at the surface of all profiles is a result of high water contents. Substitution of fresh-water by salt seawater in pores causes new changes of cation substitution and changes in clay plasticity properties. The Rasa River estuary is a typical model of river-dominated disequilibrium estuary. The sedimentation occurs under micro tidal conditions and low wave energy. An average sedimentation rate is approximately 78.000 t/yr of terrigenous matter, and average deposition rate is 0.15 m/yr. Today the Rasa River valley is one of the best locations for the harbour and the industrial development in the North Adriatic area. But, unfavourable geotechnical properties of the sediment deposit will be the main problem for the construction of the future frames. In this work are presented results of executed geotechnical investigations in the area of the RaSa River estuary and indicated properties of soils in the sediment body.