Engineering geology and Geohazards Lecture 2: The Nature of Soils Pt 2 Flashcards
What are the two classifications of soil?
Course soil (0.06mm to 63mm)
Fine soil (<0.002 to 0.06mm)
What does the table for soil particle size look like? (British standard)
(Course soils)
Gravel : 2 to 60/63mm
Sand : 0.06 to 2mm
(Fine soils)
Silt : 0.002 to 0.06mm
Clay : <0.002mm
True or false: in course soils, particles can be picked up individually and be examined by the naked eye (they are granular), as well as measured and described.
True
Additionally, particles can run through ones fingers and do stick together when saturated (incohesive).
True or false: Fine soils cannot be seen individually and are cohesive.
True
How are course soils formed?
Through mechanical weathering of the parent rock and as a result they retain mineralogical identity of the parent rock.
Fine soils are considered cohesive, What does this mean?
This means that when fine particles are saturated/wet they will stick together.
How do fine soils form?
Fine soils form through chemical weathering of the parent rock and the formation of clay minerals. E.g. Kaolinite, Illite and montmorillonite.
Describe clay mineral particles
Clay mineral particles are plate like or flaky. This results in their behavior and structure being influenced significantly by surface forces and electro-chemical interactions between the water and mineral surfaces.
Define the process of liquefaction
Liquefaction is in saturated granular soils, the water in the voids between granules exerts a pressure on the surrounding soil particles. At the time of an earthquake this pressure increases to the point where particles are able to readily move with respect to one another.
When soil substantially loses strength or stiffness during an earthquake.
Define Soil sheer strength
The ability of soil to withstand and oppose lateral deformation or sliding along internal surfaces.
The sheer strength is determined in the friction generated between soil travelling downward and the stationary soil.
Define an expansive soil
Soils which experience large amounts of swell/volume increase when water is added/is saturated.
Define cohesion
Cohesion is controlled by bonding between soil
particles due to the electrochemical interactions between
water and soil minerals present in cohesive soils.
In terms of soil shear strength, define the angle of repose
The steepest angle or slope at which loose granular material(e.g. sand) can rest without additional support.
In terms of soil shear strength, define the mouldability
The mouldability is the ability of soils to mould together and stick together (like playdoh). If they have good mouldability, this shows good cohesion.
Define soil permeability
Soil permeability is how easy water is able to move through different types of soil.
Loose granular soil has higher soil permeability.
Fine soils have poorer permeability.
