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Engineering Properties of Soils Soil Types

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Engineering Properties of Soils Soil Types Engineering Properties of Soils foundation for the project construction material (road embankments,earth dams) – PowerPoint PPT presentation

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Title: Engineering Properties of Soils Soil Types


1
Engineering Properties of Soils Soil Types
  • Engineering Properties of Soils
  • foundation for the project
  • construction material (road embankments,earth
    dams)
  • Soil Definition (Engineering)
  • refers to all unconsolidated material in the
    earths crust, all material above bedrock
  • mineral particles (sands, silts, clays)
  • organic material (topsoil, marshes) air
    water

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
    gtrounding and reducing their size
  • soils formed are called granular soil type
  • grains are similar to the original bedrock

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

4
Engineering Properties of Soils Mineral Soils
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

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

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

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
9
Engineering Properties of Soils Soil Types
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

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

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

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

14
Engineering Properties of Soils Mass-Volume
Relationships
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 2.70. Find r, rD,
    w, e, S and n
  • Given
  • Mw M - MD 70g
  • MD 230g
  • M 300g
  • V 175cm3

Air
Water Solids
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 )
  • 175 - 155 20 cm3
  • VA 20 cm3
  • VW 70 cm3
  • VD 85 cm3
  • V 175 cm3

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

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 1w
  • 3. Void Ratio is given and RD assume a unit
    volume of soil solids VD 1 m3

19
Engineering Properties of Soils Mass-Volume
Relationship
  • Density Index
  • Field soil condition referred to as loose or
    dense
  • Density Index is insitu soils 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

20
Engineering Properties of Soils
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

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

23
Engineering Properties of Soils Sieve Analysis
24
Engineering Properties of Soils Classification
Tests
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

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)

27
Engineering Properties of Soils Classification
Tests
  • Curve A - Uniform Soil
  • Curve B - Well Graded Soil
  • Soil B
  • Effective size .09 mm
  • Cu 7/.0978
  • Cc 1.12/(7x.09)1.9

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 4.75 mm - 0.075 mm (No.4-No. 200)
  • Silt 0.075 mm - 0.005 mm
  • Clay smaller than 0.005 mm
  • Identify of the grains as classified

29
Engineering Properties of Soils Classification
Tests
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/cs where soil is plastic

31
Engineering Properties of Soils Classification
Tests
32
Engineering Properties of Soils Classification
Tests
  • Atterberg Limits test measures the consistency of
    the soil deposit
  • Soil A Wp25 Wl32 w/c35
  • Soil B Wp40 Wl80 w/c45
  • Atterberg Limits Test
  • soil rolled into a thread Wp
  • soil flow measured in a cup Wl

33
Engineering Properties of Soils Soil
Classification
  • Unified Soil Classification ASTM D2487
  • general engineering purposes
  • AASHTO Soil Classification
  • highway engineering purposes
  • classifies soils to its suitability as a
    subgrade
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