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New England Soils 101

New England Soils 101

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New England Soils 101

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  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 > 3” <2 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 >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]

  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 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?