Effective stress and seepage Flashcards
How dow we characterise soils?
- Particle size distribution curves
- Atterberg limits
- Moisture
- Colour
- Fabric
- Strength
- Compressibility
What do water content profiles show?
Measuring mass of water in contrast to mass of solids
What is the Volume of Voids?
Total volume - volume of solids
What is the formula of volume of solids?
V_s = M_s/G_sρ_w
What is void ratio calculation?
e = V_v/V_s
What is porosity formula?
n = V_v/V
How can we relate n and e?
n = e/(1+e)
How can we relate e and v?
v = 1 + e where v is specific volume
What is a saturated soil?
All voids completely full with water
What is an unsaturated soil?
Some voids contain water
What is usually the unit weight of soil?
20
What are the main focuses in structures?
- Stability
- Deformations -> need factor of safety
What is soils factor of safety?
3
How do we assess loads?
Understand the response of the materials, often in terms of their Youngs modulus
What is effective stress equal to?
σ’ = σ - u
What are changes in stress due to?
Compression, distortion and a change in shearing resistance are exclusively due to changes in the effective stress
What is the angle of repose?
Angle at which soil rests at and is a strength characteristic
What is pore water pressure expressed in terms of when its negative?
suction
How do you calculate the suction?
s = u_a - u_w
, where u_a = pore air pressure
When you add more water to a soil what happens?
Radius of curvature of the meniscus increases and surface tension decreases
What is another formula for suction?
s = 2T_s/r
How can the total stress be found?
Determined by the thickness multiplied by the bulk unit weight for all material layers
Why will it take longer for capillary action to occur in fine grained material?
Because it has lower permeability
In hydrostatic scenarios what does not occur?
Seepage