classifications of soils
TRANSCRIPT
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Classification, EngineeringProperties & Consolidation
Methods
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Why Do We Classify Soils?
From experience and historic data, we know theengineering behavior of most soil types:
Strength when wet
Strength when loaded Behavior when disturbed (earthquake, vibration)
From the historic data and research of our predecessors,soil classification systems have been developed.
Therefore, if a soil can be classified accordingly, we canpredict its behavior under specific conditions
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Silt: What is It?
Silt is VERY fine sandProduced by the mechanical weathering of rock
Grinding by glaciers,
sandblasting by the wind, water erosion of rocks on the beds of rivers and streams.
Silt particles are larger than clay but smaller thansand.
Mineralogically, silt is mainly quartz and feldsparSilt is sometimes known as 'rock flour' or 'stone dust'
http://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Sandblastinghttp://en.wikipedia.org/wiki/Erosionhttp://en.wikipedia.org/wiki/Stream_bedhttp://en.wikipedia.org/wiki/Clayhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Quartzhttp://en.wikipedia.org/wiki/Feldsparhttp://en.wikipedia.org/wiki/Feldsparhttp://en.wikipedia.org/wiki/Quartzhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Clayhttp://en.wikipedia.org/wiki/Stream_bedhttp://en.wikipedia.org/wiki/Erosionhttp://en.wikipedia.org/wiki/Sandblastinghttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Weathering -
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Engineering Properties of Silt
Little or no dry strength
Non-plastic
Volume change (settlement) under load is rapid
Moderate to low permeability
Susceptible to frost heave
Minimal changes in volume due to wet/dry
VERY DIFFICULT TO COMPACT
VERY DIFFICULT TO EXCAVATE BELOW WATER TABLE
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Clay: What is it?
Produced by the chemical weathering:
Low concentrations of naturally occurring
solvents migrate through rock and takemineral particles along.
Clay deposits are formed as the result ofdeposition after they have been eroded andtransported from their original location offormation.
http://en.wikipedia.org/wiki/Chemicalhttp://en.wikipedia.org/wiki/Solventshttp://en.wikipedia.org/wiki/Solventshttp://en.wikipedia.org/wiki/Chemical -
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Engineering Properties of Clay
Clay particles are plate-shaped & have highly charged surfaces
The electrical charge on the surface attracts and holds water.
Strongest when dry due to cohesion of particles
Plastic when wet & over a range ofw%
Load carrying capacity is linked to load history Previously compressed = higher current strength
Settlement occurs over time (under static load)
Not compressible under dynamic load
Susceptible to freeze-thaw
Volume changes due to wet/dry
Easy to compact in thin layers (lifts)
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Consolidation of Clay Soils
Spring analogy :
Consolidation is explained with an idealized system composed of a spring,a container with a hole in its cover, and water. In this system, the springrepresents the compressibility of the soil, and the water which fills thecontainer represents the pore water in the soil.
http://en.wikipedia.org/wiki/Spring_%28device%29http://en.wikipedia.org/wiki/Image:Consolidation_spring_analogy.jpghttp://en.wikipedia.org/wiki/Image:Consolidation_spring_analogy.jpghttp://en.wikipedia.org/wiki/Image:Consolidation_spring_analogy.jpghttp://en.wikipedia.org/wiki/Image:Consolidation_spring_analogy.jpghttp://en.wikipedia.org/wiki/Image:Consolidation_spring_analogy.jpghttp://en.wikipedia.org/wiki/Spring_%28device%29 -
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1. The container is filled with water, and the hole is closed. (Fullysaturated soil)
2. A load is applied onto the cover, while the hole is still unopened.At this stage, only the water resists the applied load.(Development of excessive internal pore pressure)
3. When hole is opened, water starts to drain out through the holeand the spring shortens. (Loss of excessive pore water)
4. After some time, the drainage of water no longer occurs. Now,the spring alone resists the applied load. (Full dissipation of
excessive pore water pressure. End of consolidation)
http://en.wikipedia.org/wiki/Image:Consolidation_spring_analogy.jpg -
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Sheeps Foot Roller or Static Roller
Applies heavy load in a slow/rolling action.
Used to compact cohesive soils in lifts
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Consolidation of Granular Materials
It is necessary to densify loose granular soils toachieve acceptable foundation performance ofstructures.
Compaction of granular soils is achieved byvibration:
By use if a vibrator roller
By frequent drops of a large mass from a great height (deepdynamic compaction).
By insertion of a large vibrating poker into the ground (vibro-compaction
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Vibratory Roller
Used to compact sand & gravel
Delivers a dynamic blow as it rolls
Shakes particles into a more dense configuration
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Vibro-Compaction
PenetrationThe vibroprobe penetrates to the requireddepth by vibration and jetting action ofwater and/or air
CompactionThe vibroprobe is retracted in 0.5 mintervals. The in situ sand or gravel isflowing towards the vibroprobe.
CompletionAfter compaction the platform needs tobe leveled and eventually rollercompacted at the surface.
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The principle of sand compaction (Vibroflotation):
The compaction process consists of a flotation of the soil particles as a resultof vibration, which then allows for a rearrangement of the particles into adenser state.
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Test Pattern
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Deep Dynamic Compaction
Natural soil deposits and undocumented fills can bedensified by dropping large weights from great heightsrepeatedly on the ground surface.
The energy imparted is considerable & compaction canbe achieved at significant depths below the groundsurface.
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This mass of concrete, weighing about 12,000 pounds, was used for deep
dynamic compaction at the site of an oil storage tank in Japan.
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Here the mass is lifted toa height of 50 feet andis ready to be dropped.When it hits the
surface of the ground,the blow will impartabout 600,000 foot-
pounds of energy.
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These craters are the result of dropping the weight.
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The treatment pattern, energy level, number of passes and phasing of passes aredesigned based on soil conditions, required bearing capacity and settlement
characteristics.