EXAM 1 Flashcards
Void Ratio
e = Vv / Vs
Porosity
n = Vv / V
Void Ratio and Porosity Relations
e = n / (1-n) n = e / (1+e)
Degree of Saturation
S = Vw / Vv
Water Content
w = Ww / Ws = Mw / Ms
Total Unit Weight
γ = W / V
Dry Unit Weight
γd = Ws / V
Relationship between γ and γd
γ = γd * (1+w) = Ws * (1+w) / V
Unit Weight of Water
γw = 9.81 kN/m^3
= 62.4 lb/ft^3
Solid Unit Weight
γs = Ws / Vs
Specific Gravity
Gs = γs / γw
G water = 1 @ 4 C
Total Density
ρ = M / V
Dry Density
ρd = Ms / V
Solid Density
ρs = Ms / Vs
Density and Unit Weight Relation
γ = ρ * g g = 32.2 ft/sec 9.81 m/sec
Coarse
Rel bigger
Large voids
Low SSA
Equidimesnsional
Fine Soil
Very small voids
Large SSA
Platy shape ( sheets of paper )
Important surface forces
Main Mineral Group
Silicates
Basic Structural Unit of Silicates
Silica Tetrahedron
Composition of Coarse Materials
Gravel and sand fractions of soil are composed of non-clay materials
Quartz
The building blocks for clay materials
Silica Sheets
Octahedral Sheets (Tri and Di Octahedral)
Dioctahedral
Octahedral sheet with +3 element such as Al instead of +2 element
More holes than trioctahedral
Trioctahedral
Formed by octahedral units consisting of 6 hydroxyl (OH) surrounding an magnesium atom
Kaolinite
1:1 or 2 sheets per layer One silica sheet and one tetrahedral sheet Large platy shaped particle Strong glue between layers Low SSA (5-15 m2/g)
Isomorphous Substitution
Occurs in the formation of silicate materials
Substitution of one atom for another
Instead of Si atom +4 there is Al atom +3
Net unit charge deficiency increases
Distortion of the lattice
Illite
2:1 or 3 sheets per layer More charged than kaleonite Octahedral sheet bonded to 2 silica sheets Glue is not very strong Platty shaped particles Low SSA (80-100 m2/g)
Montmorillonite
2:1 or 3 sheets per layer
Dicotahdedral sheet bonded to 2 silica sheets
Cations can quickly come in and out (loose)
Due to small amount of iso sub makes exchangeable
Large amount of water in the space of the layers
Modest amount of glue ( Na, Ca, Mg)
Very high SSA
Specific Surface Area
SSA= Surface Area / mass
The two faces of all platy particles have a
The edges of particles have
Negative charge caused by iso sub that is not neutralized by interlayer cation bonding
Positive charge
Diffuse Double Layer (DL)
When water is present cations and anions can float around the clay particles forming a diffuse double layer
The water is held to the clay particles by forces of attraction
Richer in cation the close to the particle
Absorbed water layer
The first 10-15 Angstroms of water adjacent to the mineral surface
Essentially acts as part of the structure of the clay particle
So close that it doesn’t freeze
Double layer repulsion
Water molecules want to enter the double layer to reduce cation concentration by separating particles by reducing alkalinity which creates an edge to face electrical attraction
Flocculate
Two particles tend toward each other and become attached edge to face
Disperse
Two particles tend to move away due to no attraction
Unified Soil Classification System (USCS)
Standard soil identification test baed on particle size analysis and Atterberg limits
Soil types - Gravel, sand, silt, clay organic, peat
Gravel
less than 50% passing sieve #4 (4.75 mm)
Sand
more than 50% passing sieve #4 (4.75 mm)
less than 50% passing sieve #200 (0.075 mm)
Silt (M)
More than 50% passing sieve #200 (0.075 mm)
Below A-line
Clay (C)
More than 50% passing sieve #200 (0.075 mm)
On or above A-line
Organic (O)
More than 50% passing sieve #200 (0.075 mm)
(Liquid Limit dried / Liquid Limit not dried) less than 0.75
Peat (Pt)
More than 50% passing sieve #200 (0.075 mm)
Mostly organic matter
Particle Size Distribution Plot
Logrimithic Scale x axis - Particle Size (mm) y axis - Percent Finer by Weight s curve use to find percent finer than 0.075 mm
Soil Uniformity Coefficient
Cu = D60 / D10 = Diameter at 60% / Diameter at 10%
The higher Cu , the less uniform the soil, more horizontal curve
Cu = 1 means very uniform, straight curve
Coefficient of Curvature or Gradation
Cc = (D30)^2 / (D10 * D60)
Smaller and higher numbers show gaps in the curve (two types of soil)
Plasticity Atterberg Limits
Liquid Limit, Plastic Limit, Shrinkage Limit
Liquid Limit
Fluid soil-water mixture
The water content (%) after 25 blows of Casagrande cup
Plastic Limit
Enough water where the soil doesn’t crack after working with it
Water content at which 1/8” diameter thread crumbles
Plasticity Index
The difference between the liquid limit and plastic limit
PI = LL - PL
Equals the water content within which soil is in the plastic state
Compaction
Densification of soil by the application of mechanical energy
Methods of compaction
Fine : Impact and kneading using rollers controlled by relative compaction
Coarse : Static or dynamic/ vibration using vibratory and tamping controlled by relative density
Proctor Test
A compaction test to determine the optimum moisture content and density for a soil
Compactive Effort
Measure of the mechanical energy applied to the soil mass
The more applied, the more dense the material and dry unit weight increases
4 key variables in compaction of fine grained soils
- Dry density or dry unit weight
- Water content
- Compactive effort
- Soil type
Optimum water content is located on proctor test plot
Where the dry unit weight (densification) is maximized
Parabolic shape on on proctor test plot
Water acts as lubricant until a point
The compaction curve never reaches 100% saturation
Due to voids
On proctor test plot, as compactive effort increases
The dry unit weight increases and the optimum water content decreases (left)
On proctor test plot, as plasticity increases
Dry unit weight decreases
