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Marine clay is a type ofclay found in coastal regions around the world. In the northern, deglaciated regions, it can sometimes bequick clay, which is notorious for being involved in landslides.
Marine clays vary widely inmineral composition,organic matter,acidity,salinity, andmoisture. They originate from multiple sources, including weathered terrestrial rocks transported to the sea,volcaniclastics, the remains ofmarine organisms, and minerals thatprecipitate directly fromseawater. Their final structure and properties depend on regional geological conditions such astectonic activity,erosion, andsediment deposition. In addition to their sources, marine clays are shaped by theirstress history andenvironmental factors, including interactions between water and minerals, fluctuations in water levels caused bytides orclimate change, and variations insalinity andacidity.[1]
Marine clay is a particle of soil that is dedicated to a particle size class, this is usually associated with USDA's classification withsand at 0.05mm,silt at 0.05-.002mm andclay being less than 0.002 mm in diameter.[2]Paired with the fact this size of particle was deposited within a marine system involving theerosion andtransportation of the clay into the ocean.
Marine soil particles can become suspended in water; heavier sand settles quickly, while finer silt and clay particles remain suspended longer. Marine clay particles, being very small and oftennegatively charged, can resistsettling and sometimes staysuspended indefinitely, this is also known asturbidity, in which suspended particles create a murky brown color.[3]
Once the clay is deposited on the ocean floor it can change its structure through a process known asflocculation, process by which fine particulates are caused to clump together or floc. Inestuarine systems, the changes inphysicochemical conditions from the river side to the sea side triggers flocculation and leads to estuarinesiltation. This is one of the main causes for thedredging activities in harbors.Organic matter in particular plays a major role in marine clay flocculation as it can adhere to marine clay particles. Particles can also beaggregated or shifted in their structure besides being flocculated.[4]
This basic structure of clay minerals consists of onecation, usuallysilica oraluminum surrounded byhydroxideanions, these minerals form in sheets, known as clay particles, and have very specific properties to them including microporosity which is the ability of clay to hold water against the force of gravity,shrink swell capacity andabsorption capabilities. There are two basic types of sheets in clay minerals, thetetrahedralsilica sheets, and theoctahedralaluminum ormagnesium sheets.[5]
Marine clay particles can adopt different arrangements, and their structure and behavior depend on the types of exchangecations (charged ions ofsodium,potassium, orcalcium) that attach to them. Different cations lead to different arrangements and therefore different properties of the clay.[6]
When clay is deposited in theocean, the presence of excess ions in seawater causes a loose, open structure of the clay particles to form, a process known asflocculation. Once stranded and dried by ancient changing ocean levels, this open framework means that such clay is open to water infiltration. Construction in marine clays thus presents ageotechnical engineering challenge.[7]
Where clay overlies peat, a lateral movement of the coastline is indicated and shows a rise in relative sea level
Swelling of marine clay has the potential to destroybuilding foundations in only a few years. Due to the changes in climatic conditions on the construction site, the pavement constructed on the marine clay (as subgrade) will have less durability and requires lot of maintenance cost. Some simple precautions, however, can reduce the hazard significantly[citation needed].
The swapping of this positivecation with another is what makes different types of clays includingKaolinite,montmorillonite,smectite andillite. This happens in marine clays because the ocean's water is high in solution with cations making it very easy to overcome the clays negative net charge and swap the clays cation with a less positive one. These marine clays can be what are known as quick clays, which are notorious for its erosive properties. A great example of these quick clays is in thePacific Northwest. They are known asblue goo which is a mix of clay andmélange (greenstone,basalt,chert,shale,sandstone,schists. uplifted through theaccretionary wedge). These quick clays have a very high-risk factor associated with them if they are built upon, as they are very unstable due to the fact thatliquefaction happens when it becomessaturated and literally flows, causing mass wasting events to happen.
Geotechnical problems posed by marine clay can be handled by various ground improvement techniques. During the construction ofMarina Barrage inSingapore, marine clay was found at the site. Given the known risk of soft marine clay in deep excavations, foundation design for the Marina Barrage project incorporated extensivegeotechnical analysis that anticipated theground response of the marine clay encountered at the site.[8]
Marine clay can be stabilized by mixing it withcement andfly ash binding materials in specific proportions.[9]Dredged marine clay can be adapted asroadbed using wastes of various industries.[10]
Marine clays have been used in ancient and traditional ceramics for heat resistant ceramics products likecookware, andrefractory bricks.[11]Clay layers in soils which can be used as an impermeable layer are very important for dumps orchemical spills as they have a very high absorption capacity for heavy metals. For these clays to be available for human use they must have been eroded, deposited on the ocean floor and thenuplifted through means oftectonic activity to bring it to land.
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