Shallow-water sediments found near the shorelines of Kaneohe and Kailua bays on the island of Oahu, an area that has seen continuous development over the last 40 years, were tested to determine the influence of terrigenous input on the geotechnical behavior of marine calcareous sediments of biogenic origin. Consolidation and drained triaxial tests indicate that mixed sediments have higher compressibilities and lower strengths compared to high-carbonate sediments. Differences in gradation among high-carbonate sediments do not seem to have a large effect on consolidation and triaxial behavior. Due to contrasting mineralogies between the land-derived volcanic soils and the calcareous sediment of marine origin, carbonate content is a useful property that serves as an index to stress-strain and strength behavior.
The island of Oahu is part of the Hawaiian-Emperor volcanic chain stretching across the western half of the North Pacific ocean. Oahu has four major geomorphic provinces: The Koolau and Waianae ranges, the Schofield Plateau, and the Coastal Plain. Volcanic activity responsible for the formation of the Koolau and Waianae ranges ceased some 2.2 million years ago, whereas secondary volcanic activity may have stretched from about a million years to as recently as 32,000 years ago (Steams, 1985). Intense weathering of the parent basaltic lava flows in a sub-tropical setting, in conjunction with tectonic and eustatic sea level fluctuations, have resulted in a complex sequence of marine and terrestrial sediments in the Coastal Plain province. Marine sediments consist primarily of calcareous gravels, sands, and muds. This article discusses geotechnical properties of surficial calcareous and mixed shoreline sediments found on the northeast or windward coast of Oahu, an area which is under continuous pressure for further urbanization. Sediments tested for this study were obtained from Kaneohe Bay and Kailua Bay (Figure 1).
