new england soils 101
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New England Soils 101. October 8, 2009. 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. - PowerPoint PPT PresentationTRANSCRIPT
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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 depositsGlacial TillGlacial 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:
Soil Condition
Equipment/Visual
Standard Penetration Test (blows/foot)
Cohesionless Cohesive
Loose
Medium Dense
Dense to Very Dense
Hard
Very SoftSoft
Medium
Stiff
Very Stiff
Man standing sinks > 3”
Man walking sinks 2” - 3”
Man walking sinks 1”
Pickup truck ruts ½” – 1”
Loaded dump truck ruts 1” – 3”
Insignificant rutting by loaded dump truck
<2
2-4
4-8
8-15
15-30
>30
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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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116
118
120
122
124
126
128
130
132
134
136
138
140
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148
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0
Moisture Content (%)
Dry
Den
sity (p
cf)
Uncorrected Density
Corrected Density100 % Saturation
Moisture Density Relationship [Proctor Test]
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RANGE
Moisture Density Relationship [Proctor Test]
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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 1990’s 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 > 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 > 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 10”x10” to 16”x16”,
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?