Midterm Prep Flashcards
Void Ratio (Formula)
e
e=Vv / Vs
Relationship between void ratio and:
1. Density
2. Strength
3. Permeability
- As e decreases density increases
- As e decreases strength increases
- As e decreases permeability decreases
Porosity (Formula)
n
n = Vv / Vt
Degree of Saturation (Define and Formula)
Sr
Degree of Saturation tells us the percentage of the total volume of voids that contain water
Sr = Vw / Vv x 100%
Density (Formula and Units)
g/cm^3, kg/m^3 or Mg/m^3
Density of Solids, ps = Ms / Vs
Density of Water, pw = Mw / Vw = 1.0g/cm^3
Bulk Density, p = Mt / Vt
Saturated Density, psat = Mt / Vt
Dry Density, pd = Md/Vd = Ms / Vt
Buoyant (Submerged) Density, p’ = psat - pw
Unit Weight (Formula and Units)
γ = pg
kN/m^3
Moisture Content (Define and Formula)
Moisture Content is the amount of water present in a soil in terms of the mass in dry soil.
w = Mw / Ms x 100%
Specific Gravity (Formula)
Gs = γs / γw = ps / pw
Relative Density (Formula)
Dr = (emax - e) / (emax - emin) x 100%
Dr = 100% -> Very Dense
Dr = 0% -> Very Loose
* Can also be expressed in terms of unit weight or density, but you must multiply the fraction by (γdmax / γd) or (pdmax / pd)
List the main differences between Cohesive Soil and Cohesionless Soil
Cohesive:
- Fine Grained
- Grain to grain attraction (force is required to pull the material apart)
- Significantly compressible
- Moisture Content
Cohesionless:
- Course Grained
- No grain to grain attraction
- Very slightly compressible
- No moisture content
Atterberg Limits
Atterberg Limits are really moisture contents of the soil which define the change in behavior from:
Liquid to Plastic - Liquid Limit wL
Plastic to Semi-Solid - Plastic Limit wP
Semi-Solid to Solid - Shrinkage Limit Ws
Plasticity Index, PI
The plasticity index defines the range of water contents over which the soil behaviour is plastic.
PI = wL - wP
High PI indicates considerable clay minerals present.
Low PI indicates a silty material.
Liquidity Index, LI
The liquidity index provides an index to whether the soil will behave in a brittle, plastic, or sensitive manner.
LI = (wN - wP) / PI
LI = 0 -> Plastic Limit
LI < 0 -> Semi-Solid Behaviour
LI = 1 -> Liquid Limit
LI > 1 -> Sensitive (quick) Clay
Sensitivity of Soil
Sensitivity relates the undisturbed strength of the soil to its remolded strength.
When the Liquidity Index is higher than unity, the soil is said to be sensitive.
Sensitivity = (undisturbed undrained strength) / (remolded undrained strength)
Activity, A
Activity is an index that isolates the effect of the clay mineral type.
A = PI / Clay Fraction
Well Graded Soil (Define and Describe the Curve)
A good representation of particle sizes over a wide range.
Gradation Curve is usually smooth, least steep slope.
Poorly Graded Soil (Define and Describe the Curve)
Either excess or a deficiency of certain sizes, or most of the particles are about the same size. (Uniform Soil)
Gradation Curve is very vertical
Gap Graded Soil (Define and Describe the Curve)
A proportion of grain sizes within a specific range is low.
Also poorly graded.
Gradation curve is a bumpy version of a well graded soil.
Coefficient of Uniformity (Formula)
Cu = D60 / D10
1 < Cu < 5 - Uniform Soil (Narrow Range)
Cu > 15 - Well Graded Soil (Wide Range)