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New England Soils 101

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.

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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?

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