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New England Soils 101

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Title: New England Soils 101


1
New EnglandSoils 101
  • October 8, 2009

2
New England Soil
  • Soil is not like concrete or steel
  • Soil is not always homogenous
  • Soil is generally reviewed at the surface
  • Soil is one of the few construction materials
    with variable design criteria
  • Need to involve a geotechnical engineer

3
New England Geology - Soil
  • Generally glacial soil underlain by shallow
    bedrock with some marine and post glacial
    deposits
  • Glacial Till
  • Glacial Lake glaciolacustrine
  • Glacial River glaciofluvial or outwash
  • Marine Deposit sand, silt, clay
  • Post Glacial River alluvial, fluvial, and
    organics

4
New England Geology - Bedrock
  • Igneous
  • Granite
  • Schist
  • Basalt
  • Metamorphic
  • Gneiss
  • Phyllite
  • Sedimentary
  • Shale
  • Sandstone

5
Soil Design Criteria
  • Depends on
  • Density
  • Grain size soil type
  • Moisture content
  • Maximum past pressure

6
Soil Density Evaluation
  • Test boring with Standard Penetration Test SPT
  • Cone Penetrometer Test CPT
  • Density Gauge
  • Nuclear Densometer
  • Balloon
  • Sandcone

7
Estimating Soil Density
Estimate Consistency By
Standard Penetration Test (blows/foot)
Soil Condition
Equipment/Visual
Cohesionless
Cohesive
Very Soft
Man standing sinks gt 3
lt2
Loose
Soft
Man walking sinks 2 - 3
2-4
Medium
Man walking sinks 1
4-8
Stiff
8-15
Pickup truck ruts ½ 1
Medium Dense
Very Stiff
15-30
Loaded dump truck ruts 1 3
Insignificant rutting by loaded dump truck
Dense to Very Dense
Hard
gt30
8
Fundamentals of Compaction
  • Soil compaction is the action of increasing the
    density of the soil through manipulation, by
    pressing, ramming or vibrating the soil particles
    into a closer state of contact
  • Appropriate soil compaction requires
  • Lift thickness
  • Moisture content
  • Equipment
  • Proctor Value

9
Fundamentals of Compaction Mechanics
  • The mechanics of consolidating fine-grained soil
    is very complex involving capillary action, pore
    pressure, permeability, and other factors.
  • What are fine grained soils?
  • Impacts of water
  • Past pressure influence

10
Standard Proctor ASTM D698
  • Developed prior to World War II
  • Utilizes a lower compactive effort than the
    Modified Proctor
  • 5.5 lb Hammer, 12-inch drop, 25 Blows/lift
  • Typically higher compaction requirements are
    recommended (98 Building, 95 Pavement)
  • Stone correction

11
Modified Proctor ASTM D1557
  • Developed After World War II
  • More energy onto the soil sample than the
    Standard Proctor Test
  • 10 lb Hammer, 18-inch drop, 56 blows/lift
  • Stone correction

12
AASHTO T-180 Method D
  • Recommended for reclaimed aggregates
  • Similar to Modified Proctor ASTM D 1557
  • ¾-inch plus material is removed and replaced with
    ¼-inch material
  • No stone correction is applied

13
Moisture Density Relationship Proctor Test
14
Moisture Density Relationship Proctor Test
15
Moisture Density Relationship Proctor Test
RANGE
16
Foundation Systems
  • Shallow foundations
  • Ground improvements
  • Deep foundations

17
Shallow Foundations
  • Most common foundation type
  • Minimal engineering low tech
  • Generally have the most risk of settlement

18
Spread Footings
  • Design based on soil bearing pressure
  • Typically constructed to frost depth
  • Shape square, rectangular, strip
  • Usually min 3,000 psi concrete
  • Economical

19
Reducing Risk
  • To reduce risk you need to understand the geology
    and implement recommendations of the geotechnical
    report
  • Bearing capacity review
  • Verify correct soil
  • Evaluate proofrolling
  • Evaluate compaction of fill
  • Appropriate use of geotextiles

20
Geotextiles
  • Non-woven geotextile filter
  • Woven geotextile filter and improves stability
  • GeoGrid improves stability

21
Shallow Foundation Pitfalls
  • Frozen subgrades
  • Existing fill conditions
  • Use of crushed stone

22
Ground Improvements
  • Preload/surcharge
  • Deep dynamic compaction
  • Rammed aggregate piers
  • Soil stabilization

23
Preloading/Surcharge
  • Can be used for shallow and deep cohesive or
    organic soils
  • Requires placing fill to design loads before
    construction
  • Pre-evaluation of settlement and time
  • Used with or w/o wick drains to speed settlement
  • Verify by monitoring settlement

24
Preload/Surcharge
25
Deep Dynamic Compaction
  • High energy densification of soils up to 40 feet
    deep
  • More suitable for granular deposits
  • Systematic dropping weights from 40 to 80 feet.
    Energy required is a function of depth of
    improvement and soil conditions
  • Verify with borings or crater measurements

26
Rammed Aggregate Piers
  • Compacted aggregate shafts Patented 1990s
  • Improved bearing capacity replace mass
    excavation greater than 5 to 6 feet
  • Allows spread footings/soil supported slabs
  • 24 to 30 inch diameter 10 to 30 feet deep,
    spacing 8 to 12 feet
  • 20 to 40 ton capacity, verify w/ modulus test

27
Soil Stabilization
  • Soil mixed with cementitious materials at surface
    or in columns
  • Grouting
  • Compaction
  • Jet
  • Chemical
  • GeoGrid

28
Deep Foundations
  • Driven Piles
  • Steel HP Sections
  • Steel Pipe or Shell
  • Pre-cast Prestressed Concrete
  • Timber
  • Pressure-Injected Footing (PIF)
  • Drilled Shafts
  • Drilled Mini-Piles

29
Steel H-Piles
  • 60 to 120 tons
  • End-bearing
  • Full penetration welded splices
  • Capacity gt 50 tons require load test

30
Steel Pipe Piles
  • 65 to 125 tons
  • End-bearing typically
  • Welded base plate w/ full penetration welded
    splices
  • Capacity gt 50 tons require load test
  • 3,000 to 4,000 psi concrete filled

31
Pre-cast Pre-stressed Concrete Piles
  • 70 to 135 tons
  • End-bearing or friction
  • Splicing possible but difficult
  • 4,000 psi concrete
  • 10x10 to 16x16, square or octagonal cross
    section
  • Lengths w/o prestress 40 to 50 feet
  • Lengths w/ prestress 130 feet max

32
Treated Timber
  • 15 to 25 tons
  • End-bearing or friction
  • Typical length 35 to 45 ft., max 50 to 55 feet,
    non spliceable
  • CCA treated

33
Pressure-Injected Footings
  • Also known as Frankie Pile
  • 50 to 150 tons
  • Bottom driven thick walled drive tube
  • High energy rammed concrete base
  • 3,000 to 4,000 psi poured or rammed concrete
    shaft
  • 10 to 35 feet deep
  • Load test required

34
Drilled Shafts
  • 100 to 500 tons
  • End-bearing and friction
  • Often rock-socketed for high capacity
  • 30 inch to 120 inch diameter
  • 3,000 to 4,000 psi concrete
  • Cost 350 to 450/cy
  • Load test required

35
Drilled Mini-Piles
  • 20 to 150 tons
  • Friction based, minor end-bearing
  • Often rock-socketed for high capacity
  • 4 to 8 inch diameter
  • 4,000 to 5,000 psi grout w/steel center bar
  • Installed w/ temp steel casing

36
  • Questions?
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