Quaternary / Lacustrine / Plasticity / Montmorillonite

• Quaternary Deposits:

  • Quaternary are deposits during the Quaternary period, the most recent (and current) geological period. 
  • Quaternary deposits are young and therefore may not have been consolidated much making them susceptible to erosion because they are less compacted and less cemented
• Origin of Lacustrine:      

  
  

  •  Lacustrine = deposits by or from a lake. 
  •  Typical lacustrine deposit = clay. 
• Plasticity

  • Plasticity = ‘plastic index’ = difference between plastic limit and liquid limit. 
  • Plasticity indicates potential for soils to absorb water (usually the more clay in the soil the more plastic it is). 
• Montmorillonite

  Clay mineral formed by weathering of igneous rocks in warm climates
• Montmorillonite - water content

  • Montmorillionite = A Clay mineral particularly prone to shrinking and swelling in response to changes in water content.
  • Clay mineral sheets are weakly bonded by van der waal bonds, easily separated by water with a large surface area
  • Montmorillonite has a very large specific surface area (= 800m2/g)
  • Has a large Plasticity Index
  • Allows montmorillonite clay to contain large amounts of water
• Montromorillite - water content

  Water content change could be caused by several factors such as seasonal changes, or loading from structures
• Montmorillite

  Soils such as montmorillonite clay are known as 'expansive'