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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.

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Presentation on theme: "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."— Presentation transcript:

1 New England Soils 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: Soil ConditionEquipment/Visual Standard Penetration Test (blows/foot) CohesionlessCohesive Loose Medium Dense Dense to Very DenseHard Very Soft Soft 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 < >30

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]

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15 RANGE Moisture Density Relationship [Proctor Test]

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 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

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 > 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 > 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  10”x10” to 16”x16”, 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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