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Geotechnical Investigations

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Compaction. Compaction - Densification of soil by removing air voids using ... BG soils in the summer (driest months) will have moistures around 22 to 24 ... – PowerPoint PPT presentation

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Title: Geotechnical Investigations


1
Compaction
  • Compaction - Densification of soil by removing
    air voids using mechanical equipment
  • As compaction increases, the following occurs
  • Strength increases
  • potential for settlement decreases
  • permeability decreases
  • In soils compaction a function of water content

2
Compaction
  • Consider 0 moisture - Only compact so much
  • Add a little water - compacts better
  • A little more water - a little better compaction
  • What is better compaction?
  • More solid material (not water) in the same
    volume
  • In other words - dd increases with increasing
    moisture content - TO A POINT

3
Compaction
  • At some point (varies from soil to soil)
    Increasing moisture decreases dd

4
Compaction
  • Compaction curve plotted dd vs. moisture content
  • The peak of the curve is the maximum
    compaction(dd max) and optimum moisture content
    under the specified energy
  • The energy in this case is the weight of the
    hammer and the height of the hammer drop

5
Compaction - Lab Equipment
  • Standard Proctor
  • 1/30 ft3 mold
  • 5.5 lb hammer
  • 12 drop
  • 3 layers of soil
  • 25 blows / layer

6
Compaction - Lab Equipment
  • Modified Proctor
  • 1/30 ft3 mold
  • 10 lb hammer
  • 18 drop
  • 5 layers of soil
  • 25 blows / layer

7
Compaction - Lab Equipment
8
Compaction - Lab Equipment
9
Compaction Project Specs
  • The GE will provide compaction criteria
  • Other terms for compacted fill engineered fill
    controlled fill
  • Specs will refer to Relative Compaction
  • Relative to what?
  • Proctor Test standard or modified

10
Compaction Project Specs
  • Soil will be compacted to 98 relative compaction
    as compared to a standard proctor test, ASTM
    D-698.
  • The soil moisture content will be - 2 of
    optimum. (might say 2 or -1)

11
Compaction Project Specs
  • 98 means the soil in the field should be 98 of
    the lab result
  • For example, if the peak of the curve is at 100
    pcf and 22 moisture
  • The field compaction must be at least 98 pcf and
    within the stated moisture range

12
Compaction Project Specs
  • The moisture spec is sort of an additional check
    on the soil
  • Looking at the curve, at any dd there is a window
    of potential moisture contents.
  • If the soil is too wet or too dry, it is unlikely
    it can achieve compaction
  • If the moisture is outside the range, something
    is probably not right

13
Compaction Project Specs
  • The proctor could be wrong or the soil could have
    changed. It is up to the GE to determine if it
    is ok or not.
  • Soils can vary dramatically, so at least one
    proctor should be run on every job.
  • More than one needed if soils change.

14
Compaction Project Specs
  • In Bowling Green, a standard proctor will on
    average be about 102 pcf at 22
  • MUST verify, cannot assume a value.
  • I have seen 110 pcf to 85 pcf.

15
Compaction
  • Proctor Does Not Guarantee Quality
  • It only shows compaction relative to a lab test.
  • Horse s____ can be compacted in the lab and you
    can test it in the field
  • If it passes compaction, it does not mean it is
    good
  • GE must determine 1st if the soil is acceptable
    as fill, then the compaction must pass

16
Compaction
  • Generally, the lower the PI and the higher the dd
    the better the soil will be for compaction.
  • Locally, if clay soils used as fill then some
    rock of the gravel size or slightly larger will
    make a better engineered fill.

17
Observing and Testing Compacted Fill
  • A qualified GE should be hired to properly
    observe and approve compaction
  • The GEs tools of testing fill
  • Observation of operations
  • Skill of the operator
  • Density tests

18
Observing and Testing Compacted Fill
  • The observations of the GE should include
  • Number of passes (compaction effort)
  • Lift thickness
  • Equipment (compactor, blade)
  • Soil properties, changes, type, moisture
  • Direct contractor to work the soil as needed
  • Proofroll as needed
  • Test results

19
Observing and Testing Compacted Fill
  • Problem Too much moisture
  • Solution Work the soil (move the pile)
  • Aerate
  • Let dry
  • Problem Low compaction
  • Solution More compaction effort
  • More passes
  • Thinner lifts
  • fewer passes needed
  • better productivity

20
Observing and Testing Compacted Fill
21
Observing and Testing Compacted Fill
22
Observing and Testing Compacted Fill
Proofrolling Looking for stability and no
pumping
23
Compaction Testing
Most common method is nuclear
24
Compaction Testing
  • Density test in the field determines the unit
    weight and moisture of the compacted fill.
  • Compare the field data to lab
  • Other tests include sand cone and drive tube
  • Density test alone does not tell you much
  • The other 2 tools are needed
  • Observation operator (skill equip)
  • DENSITY TESTS DONT TELL YOU STRENGTH

25
Standard vs. Modified Proctor
  • As discussed, more energy moves the compaction
    curve up and to the left
  • This decreases optimum moisture and increases dry
    unit weight
  • The standard was originally developed to simulate
    field compaction in the lab
  • The modified was developed to simulate larger
    compaction effort for more serious loads and
    bigger equipment

26
Standard vs. Modified Proctor
  • SO WHICH TO USE???
  • To the untrained eye modified seems better as
    it will get you more solid material into the same
    volume thus it will reduce potential for
    settlement, etc.
  • The trained eye will consider
  • What is needed
  • What will work
  • Soil type
  • Geographic conditions
  • Cost

27
Standard vs. Modified Proctor
  • In BG, the building types most common
  • Low rise commercial
  • Bearing capacities 2000 to 3000 psf
  • Clays
  • Climate and precipitation keep soils below grade
    consistently moist
  • Standard is the best choice in most cases here
    Why????

28
Standard vs. Modified Proctor
  • While a modified will give you better strength
    do we need it?
  • In a little league baseball dugout, would you
    spec 10000 psi concrete?
  • Why or why not
  • Dont need it, thats why
  • For most building cases would not specify
    modified (some you would which ones?) because
    you only need standard

29
Standard vs. Modified Proctor
  • What is the harm in specifying modified?
  • Cost
  • Also should consider soils and local conditions
  • In BG Standard will typically produce around
    102 pcf at 22
  • Modified will typically produce around 108 at 16

30
Standard vs. Modified Proctor
  • BG soils in the summer (driest months) will have
    moistures around 22 to 24
  • With a lot of compaction effort, moistures might
    get down to 20
  • To meet a modified, will need to get down to 17
    to 18 - Almost impossible to do
  • It can double or even triple time needed
  • Consider the situation before choosing standard
    or modified
  • Let the Geotech do it!!

31
Compaction Equipment
  • Sheepsfoot Compactor
  • Smooth Drum
  • Vibratory
  • Rubber Tire
  • Jumping Jacks
  • Plates
  • Trench Compactors

32
Compaction Equipment
33
Compaction Equipment
34
Compaction Equipment
35
Compaction Equipment
36
Compaction Equipment
37
Compaction Equipment
38
Compaction Equipment
39
Compaction Equipment
40
Compaction Equipment
41
Compaction Equipment
42
Compaction Equipment
43
Compaction Equipment
44
Compaction Equipment
45
Compaction Equipment
46
Compaction Equipment
  • Vibratory compactors most effective in
    cohesionless soils
  • Can help in clays, but not as much
  • Smooth drum for asphalt, DGA, finish grade in
    soils. Not good for initial compaction in soils.

47
Field Compaction Operations
  • Primary Factors
  • Equipment
  • Lift Thickness
  • Soil Moisture
  • Book states intensity of pressure, which is
    equipment.

48
Field Compaction Operations
  • Heavier equipment is better
  • However - heavier must be translated to contact
    area (intensity of pressure)
  • Track equipment - dozers, excavators, are heavy,
    but dont compact
  • Why?

49
Field Compaction Operations
  • Better compaction comes from?
  • 1 -
  • 2 -
  • 3 -
  • 4 -
  • etc.

50
Field Compaction Operations
  • Thin lifts always better
  • Easier to compact
  • Fewer passes needed
  • Some contractors think thin lifs slower, big
    thick lifts faster
  • Not true

51
Field Compaction Operations
  • Imagine filling a hole
  • It will take X truck loads
  • Whether you place 2 foot lifts or 2 inch lifts,
    it is X truck loads
  • Thinner lifts spread farther - less stop and
    reverse time
  • Less passes to compact 2 than 2
  • Thin lifts almost compacted by truck or scraper

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55
Homework Exercises
  • Chapter 5 problems
  • 4
  • 5
  • 8
  • Have completed for next class for discussion
    and/or turn in
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