New England Soils 101

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New EnglandSoils 101

• October 8, 2009

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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

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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

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New England Geology - Bedrock

• Igneous
• Granite
• Schist
• Basalt
• Metamorphic
• Gneiss
• Phyllite

• Sedimentary
• Shale
• Sandstone

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Soil Design Criteria

• Depends on
• Density
• Grain size soil type
• Moisture content
• Maximum past pressure

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Soil Density Evaluation

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

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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
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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

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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

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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

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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

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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

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Moisture Density Relationship Proctor Test
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Moisture Density Relationship Proctor Test
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Moisture Density Relationship Proctor Test
RANGE
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Foundation Systems

• Shallow foundations
• Ground improvements
• Deep foundations

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Shallow Foundations

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

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Spread Footings

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

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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

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Geotextiles

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

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Shallow Foundation Pitfalls

• Frozen subgrades
• Existing fill conditions
• Use of crushed stone

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Ground Improvements

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

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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

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Preload/Surcharge
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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

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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

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Soil Stabilization

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

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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

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Steel H-Piles

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

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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

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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

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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

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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

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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

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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

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• Questions?