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

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]

New England Geology - Bedrock Igneous Granite Schist Basalt Metamorphic Gneiss Phyllite Sedimentary Shale Sandstone

Soil Design Criteria Depends on: Density Grain size [soil type] Moisture content Maximum past pressure

Soil Density Evaluation Test boring with Standard Penetration Test [SPT] Cone Penetrometer Test [CPT] Density Gauge Nuclear Densometer Balloon Sandcone

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

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

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

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

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

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

Moisture Density Relationship [Proctor Test]

Moisture Density Relationship [Proctor Test]

Moisture Density Relationship [Proctor Test] RANGE

Foundation Systems Shallow foundations Ground improvements Deep foundations

Shallow Foundations Most common foundation type Minimal engineering [low tech] Generally have the most risk of settlement

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

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

Geotextiles Non-woven geotextile [filter] Woven geotextile [filter and improves stability] GeoGrid [improves stability]

Shallow Foundation Pitfalls Frozen subgrades Existing fill conditions Use of crushed stone

Ground Improvements Preload/surcharge Deep dynamic compaction Rammed aggregate piers Soil stabilization

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

Preload/Surcharge

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

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

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

Deep Foundations Driven Piles Pressure-Injected Footing (PIF) Steel HP Sections Steel Pipe or Shell Pre-cast Prestressed Concrete Timber Pressure-Injected Footing (PIF) Drilled Shafts Drilled Mini-Piles

Steel H-Piles 60 to 120 tons End-bearing Full penetration welded splices Capacity > 50 tons require load test

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

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

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

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

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

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

Questions?