classifications of soils

7/28/2019 Classifications of Soils

1/19

Classification, EngineeringProperties & Consolidation

Methods


2/19

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


3/19

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


4/19

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


5/19

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


6/19

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)


7/19

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


8/19

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


9/19

Sheeps Foot Roller or Static Roller

Applies heavy load in a slow/rolling action.

Used to compact cohesive soils in lifts


10/19

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


11/19

Vibratory Roller

Used to compact sand & gravel

Delivers a dynamic blow as it rolls

Shakes particles into a more dense configuration


12/19

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.


13/19

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.


14/19

Test Pattern


15/19

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.


16/19

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.


17/19

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.


18/19

These craters are the result of dropping the weight.


19/19

The treatment pattern, energy level, number of passes and phasing of passes aredesigned based on soil conditions, required bearing capacity and settlement

characteristics.

classifications of soils

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