The origins of soil deposits

The origins of soil deposits on the earth’s crust can reveal significant findings in the chemical and mechanical characteristics of the soils themselves. It is important to uncover such origins to find how and where such deposits may have formed over tens of thousands of years ago.

Marine and Lacustrine deposits are two soil types that are commonly encountered during soil exploration, both of which are primarily traced back to either glacial o r more broadly, alluvial origins (Hunt 2005 ). They are somewhat alike in there fine sedimentary composition and similarly can be prone to presenting engineers with problematic conditions such as h igh secondary consolidation characteristics and subsidence, potential acid sulfate soils and quick clay landslides (Das 2007). The occurrences of marine soils are found in offshore and coastal plain deposits.

It is important to note however the time scale of which marine deposition has occurred, such soils have become exposed from residing sea levels, glacial withdrawal (isostasy) and continental/tectonic plate shifts, meaning previous offshore deposits from past glaciation periods, h ave risen and are now exposed to human activity and land use. The origin of marine soils can be traced back to glacial or alluvial transportation from land runoff through river outlets (Hunt 2005). Marine deposition also occurs due to aeolian transportation through wind relocation of fine grained sediments.

One of the most iconic and well documented occurred in Rissa, Norway 1978, where a small excavation caused the disturbance and displacement of up to 5-6 million cubic meters of gently sloping farm and coastal land. The cause was due to the mechanical properties of the marine clay b eing altered after the soil was remolded, or in the case of Rissa, d isturbed by a shallow excavation. The changes in the ground conditions caused the collapse of the soil structure, p roducing an almost complete loss of shear strength , allowing the soil to form a liquid mass.