1. Engineering Properties of Soils Soil Types
foundation for the project
construction material (road embankments,earth dams)
Soil Definition (Engineering)
“refers to all unconsolidated material in the earth’s crust, all material above bedrock”
mineral particles (sands, silts, clays)
organic material (topsoil, marshes) + air + water
Soils ENCI 579

2. Engineering Properties of Soils Soil Types
Mineral Soil Particles
weathering of rock from the crust of the earth
physical weathering and chemical weathering
Physical Weathering
action of frost, water, wind, glaciers, plant/animals, etc. breaking particles away from original bedrock
particles transported by wind, water, ice >rounding and reducing their size
soils formed are called granular soil type
“grains are similar to the original bedrock”
Soils ENCI 579

3. Engineering Properties of Soils Soil Types
Chemical weathering
occurs when water flows through rocks and leaches out some of the mineral components of the rock
soils formed are called clays
“clay particles are mineral crystals that have very different properties from those of the original bedrock”
Soils ENCI 579

4. Engineering Properties of Soils Mineral Soils
Soils ENCI 579

5. Engineering Properties of Soils Soil Types
Granular and Cohesive soil types
difference in engineering properties result from the large variation in size and shape of the grains
Cohesive soil type (clays)
grains are extremely small and flat
the mass of a grain as a force is negligible when compared to the forces resulting from the surface properties of the grain
Soils ENCI 579

6. Engineering Properties of Soils Soil Types
Water Holding Capacity of Clays
Shrinkage
evaporation of exposed clays
loading
Expansion
dry side may absorb moisture
Structure of Clays
deposited by settling out in lakes
Soils ENCI 579

7. Engineering Properties of Soils Soil Types
Structure of Clays
surface charges forces grains to edge to side pattern
flocculent structure as opposed to granular soils which are deposited in a denser configuration because the force of gravity on the mass of these grains is more important
Soils ENCI 579

8. Engineering Properties of Soils Soil Types
Clays have surface charges due to the very large surface area per gram of material
Chemical composition results in:
negative charges along the sides of a grain
positive charges at the ends of a grain
Results of these surface properties
water holding capacity of clays surface charges attract water
structure of clay deposits
clay grain
Soils ENCI 579

9. Engineering Properties of Soils Soil Types
Soils ENCI 579

10. Engineering Properties of Soils Soil Types
Clay Soils
Small flat shape
Negative/positive surface charges
Bound water on the surface
Different clay minerals are different in size
Swelling clays absorb water into the crystal lattice
Shrinkage due to evaporation or loading
Soils ENCI 579

11. Engineering Properties of Soils Soil Types
Granular Soils
Larger grain sizes than clays
Particles tend to be more or less spheres/cubes
Bound water is small compared to overall mass
Silt particles may not be visible to eye but tend to be gritty, have dull appearance and lack cohesion when dry
Soils ENCI 579

12. Engineering Properties of Soils Soil Types
Organic Soils
Tend to be fibrous and/or amorphous
Brown to Black in color
High moisture holding capacity
Water may run out when squeezed
Dried organic soils may combust
Soils ENCI 579

13. Engineering Properties of Soils Soil Types
Silts are coarser than clays and not bond tightly together
Silts are gritty, less plastic and dull when cut
Dry Strength-silts loose “apparent cohesion” when dried
Shaking test-saturated silt samples become denser water seeps to the surface - “dilantancy”
Soils ENCI 579

14. Engineering Properties of Soils Mass-Volume Relationships
Soils ENCI 579

15. Engineering Properties of Soils Mass-Volume Relationships
Example 1-2
A soil sample has a volume of 175cm3 and a total mass of 300g. Mass when dried is 230g. Relative density of the soil solids is Find r, rD, w, e, S and n
Given:
Mw = M - MD = 70g
MD = 230g
M = 300g
V = 175cm3
Air
Water
Solids
Soils ENCI 579

16. Engineering Properties of Soils Mass-Volume Relationships
Calculations:
Vw = Mw/rw
= 70g/(1 g/cm3)
=70 cm3
VD = MD/(RD x rw)
= 230g/(2.70 x 1 g/cm3)
= 85 cm3
VA = V- (VD + Vw )
= = 20 cm3
VA = 20 cm3
VW = 70 cm3
VD = 85 cm3
V = 175 cm3
Soils ENCI 579

17. Engineering Properties of Soils Mass-Volume Relationships
Answer:
r = M/V = 300g/175cm3 = 1.71 g/cm3
rD = MD/V = 230g/175cm3 = 1.31g/cm3
w = Mw / MD = 70g/230 g = 30.4 %
e = Vv / VD = 90 cm3/85 cm3 = 1.06
S = VW /Vv = 70 cm3/90 cm3 = 78 %
n = Vv /V = 90 cm3/ 175 cm3 = 51 %
Soils ENCI 579

18. Engineering Properties of Soils Mass-Volume Relationships - Rules
1. Density is given assume total unit volume 1 cm3 or 1 m3
2. Water content is given along with total density or total mass.
Use MD = M or rD = r
1 + w 1+w
3. Void Ratio is given and RD assume a unit volume of soil solids VD = 1 m3
Soils ENCI 579

19. Engineering Properties of Soils Mass-Volume Relationship
Density Index
Field soil condition referred to as loose or dense
Density Index is insitu soil’s density relative to the maximum and minimum for that type of soil
Assessing the stability of granular soils
Known as relative density
ID = r DRY MAX x r D - r DRY MIN
r D r DRY MAX - r DRY MIN
Soils ENCI 579

20. Engineering Properties of Soils
Soils ENCI 579

21. Engineering Properties of Soils Classification Tests
Two types of tests used in classifying soils
Grain size, measures grain sizes
Plasticity, measures grain types
Grain Size
grain size distribution curve
Sieve analysis gravel and sand
Hydrometer test for silt and clay
Soils ENCI 579

22. Engineering Properties of Soils Classification Tests
Hydrometer Test
Used to find the size of smaller grains to plot a grain size distribution curve
Stokes Law
particles in suspension settle out at a rate which varies with their size
hydrometer measures the density of a soil-water mix at various times as the grain settles
The size of particle to the center of the bulb can be calculated and density of the solution indicates the percentage of the sample still in solution
Soils ENCI 579

23. Engineering Properties of Soils Sieve Analysis
Soils ENCI 579

24. Engineering Properties of Soils Classification Tests
Soils ENCI 579

25. Engineering Properties of Soils Classification Tests
Grain Size Distribution Curve
Shape
Uniform soil is composed of mainly one size grain
Well graded soil contains a wide range of grain sizes
Effective Size
Effective size is the grain size that only 10% of the grain sizes are finer than.
The amount and type of fine grains in a soil are important in assessing the properties of that soil
Soils ENCI 579

26. Engineering Properties of Soils Classification Tests
Grain Size Distribution Curve
Uniformity Coefficient Cu
indication of the shape of the curve and range of particle sizes that the soil contains
Cu = D60 / D10
Coefficient of Curvature Cc
indication of the shape of the curve.
Cc = (D30)2 / (D60 x D10)
Soils ENCI 579

27. Engineering Properties of Soils Classification Tests
Curve A - Uniform Soil
Curve B - Well Graded Soil
Soil B
Effective size = .09 mm
Cu = 7/.09=78
Cc = 1.12/(7x.09)=1.9
Soils ENCI 579

28. Engineering Properties of Soils Classification Tests
Textural Classification
based entirely on grain size
ASTM System
Gravel larger than 4.75 mm (No. 4)
Sand mm mm (No.4-No. 200)
Silt mm mm
Clay smaller than mm
Identify % of the grains as classified
Soils ENCI 579

29. Engineering Properties of Soils Classification Tests
Soils ENCI 579

30. Engineering Properties of Soils Classification Tests
Plasticity Test (grain type)
Measures the amount of water that a soil absorbs
Plastic Limit
w/c where the soil behaves like a plastic material
Liquid Limit
w/c where the soil behaves more like a liquid
Plasticity Index (Atterberg Limits Test)
the range of w/c’s where soil is plastic
Soils ENCI 579

31. Engineering Properties of Soils Classification Tests
Soils ENCI 579

32. Engineering Properties of Soils Classification Tests
Atterberg Limits test measures the consistency of the soil deposit
Soil A: Wp=25 Wl=32 w/c=35
Soil B: Wp=40 Wl=80 w/c=45
Atterberg Limits Test
soil rolled into a thread Wp
soil flow measured in a cup Wl
Soils ENCI 579

33. Engineering Properties of Soils Soil Classification
Unified Soil Classification ASTM D2487
general engineering purposes
AASHTO Soil Classification
highway engineering purposes
classifies soils to it’s suitability as a subgrade
Soils ENCI 579