SOIl Flashcards
BsCs considers soils in 2 categories, what are they?
Fine(>35% passing 63mm sieve)
or
Coarse (<35% passive 63mm sieve)
What size is cohesionless soil
D>0.06mm
Explain what is the Double diffuse layer,
The double diffuse layer is a region near a charged surface where ions from a solution gather, with an outer layer of ions being more spread out.
DDL role in the behaviour of clays
The double diffuse layer helps to stabilize charged surfaces and affects interactions between particles in solutions, influencing processes like colloid stability and electrochemical reactions
DDL factors
affecting its thickness (and how).
The thickness of the DDL decreases when:
* The concentration of salt increases (NaCl)
* Temperature decreases
* The valence of cations increases
2 methods to determining the Liquid Limit (LL)
Casagrande method or Falling cone method
Plasticity Index formula
PI = LL - PL
Moisture Conten Formula
W= Mw/Ms
Void Ratio Formula
Vv/Vs
Porosity
e/1+e
Degree saturation
Sr=Vw/Vs
Bulk Density formula
p=(Ms+Mw)/Vt
Density
p=M/V
Submerged Density
ρ’ = ρ - ρw
Specific Gravity formula
Gs = Ps/Pw = Ms/(Vs Pw)
(𝜌=P)
Describe in a short paragraph what critical flow conditions are about
Critical flow conditon- If the seepage force is > gravity force, the soil exerts a downward force
Ways to mitigate critical flow conditions
1.Proper design and sizing.
2.Using flow control devices.
3.Installing pressure relief systems.
4.Monitoring and controlling systems.
Comment on how the benefits of falling
head test
Suitable for materials with low to moderate permeability.
Mimics natural drainage conditions more closely by allowing the hydraulic gradient to decrease over time.
Comment on how the benefits of constant head test
Suitable for materials with high permeability.
Maintains a constant hydraulic gradient throughout the test, which simplifies calculations.
What relationship must an equipotential have with a flow line if the flow net
is to produce credible predictions of seepage flow?
For credible predictions of seepage flow in a flow net, equipotential lines must intersect flow lines at right angles.
how does cut off walls help in seapage
Cut-off walls stop water from seeping through soil or rock, preventing potential damage to structures and controlling environmental risks.
