Classification, Engineering Classification, Engineering Properties & Consolidation Properties & Consolidation

MethodsMethods

Why Do We Classify Soils?Why Do We Classify Soils? From experience and historic data, we know the From experience and historic data, we know the

engineering behavior of most soil types:engineering behavior of most soil types:

Strength when wetStrength when wet Strength when loadedStrength when loaded Behavior when disturbed (earthquake, vibration)Behavior when disturbed (earthquake, vibration)

From the historic data and research of our From the historic data and research of our predecessors, soil classification systems have been predecessors, soil classification systems have been developed.developed.

Therefore, if a soil can be classified accordingly, we Therefore, if a soil can be classified accordingly, we can predict its behavior under specific conditionscan predict its behavior under specific conditions

Silt: What is It?Silt: What is It?

Silt is VERY fine sandSilt is VERY fine sandProduced by the mechanical weathering of rock Produced by the mechanical weathering of rock

Grinding by Grinding by glaciersglaciers, , sandblastingsandblasting by the wind, by the wind, water erosion of rocks on the beds of rivers and streams. water erosion of rocks on the beds of rivers and streams.

Silt particles are larger than Silt particles are larger than clayclay but smaller than but smaller than sandsand. .

Mineralogically, silt is mainly Mineralogically, silt is mainly quartzquartz and and feldsparfeldspar Silt is sometimes known as 'rock flour' or 'stone Silt is sometimes known as 'rock flour' or 'stone

dust' dust'

Engineering Properties of SiltEngineering Properties of Silt

Little or no dry strengthLittle or no dry strengthNon-plastic Non-plastic Volume change (settlement) under load is rapidVolume change (settlement) under load is rapidModerate to low permeabilityModerate to low permeabilitySusceptible to frost heaveSusceptible to frost heaveMinimal changes in volume due to wet/dryMinimal changes in volume due to wet/dryVERY DIFFICULT TO COMPACTVERY DIFFICULT TO COMPACTVERY DIFFICULT TO EXCAVATE BELOW WATER VERY DIFFICULT TO EXCAVATE BELOW WATER

TABLETABLE

Clay: What is it?Clay: What is it?

Produced by the chemical weathering:Produced by the chemical weathering:

Low concentrations of naturally occurring Low concentrations of naturally occurring solvents migrate through rock and take solvents migrate through rock and take mineral particles along.mineral particles along.

Clay deposits are formed as the result of Clay deposits are formed as the result of deposition after they have been eroded deposition after they have been eroded and transported from their original and transported from their original location of formation. location of formation.

Engineering Properties of Engineering Properties of ClayClay

Clay particles are plate-shaped & have highly charged Clay particles are plate-shaped & have highly charged surfacessurfaces

The electrical charge on the surface attracts and holds The electrical charge on the surface attracts and holds water.water.

Strongest when dry due to cohesion of particlesStrongest when dry due to cohesion of particles Plastic when wet & over a range of Plastic when wet & over a range of w%w% Load carrying capacity is linked to load history Load carrying capacity is linked to load history

Previously compressed = higher current strengthPreviously compressed = higher current strength Settlement occurs over time (under static load)Settlement occurs over time (under static load) Not compressible under dynamic loadNot compressible under dynamic load Susceptible to freeze-thaw Susceptible to freeze-thaw Volume changes due to wet/dryVolume changes due to wet/dry Easy to compact in thin layers (lifts)Easy to compact in thin layers (lifts)

Consolidation of Clay SoilsConsolidation of Clay Soils Spring analogy : Spring analogy :

ConsolidationConsolidation is explained with an idealized system composed of is explained with an idealized system composed of a spring, a container with a hole in its cover, and water. In this a spring, a container with a hole in its cover, and water. In this system, the spring represents the compressibility of the soil, and system, the spring represents the compressibility of the soil, and the water which fills the container represents the pore water in the the water which fills the container represents the pore water in the soil.soil.

1.1. The container is filled with water, and the hole is closed. The container is filled with water, and the hole is closed. (Fully saturated soil) (Fully saturated soil)

2.2. A load is applied onto the cover, while the hole is still A load is applied onto the cover, while the hole is still unopened. At this stage, only the water resists the applied unopened. At this stage, only the water resists the applied load. (Development of excessive internal pore pressure) load. (Development of excessive internal pore pressure)

3.3. When hole is opened, water starts to drain out through the When hole is opened, water starts to drain out through the hole and the spring shortens. (Loss of excessive pore water) hole and the spring shortens. (Loss of excessive pore water)

4.4. After some time, the drainage of water no longer occurs. After some time, the drainage of water no longer occurs. Now, the spring alone resists the applied load. (Full Now, the spring alone resists the applied load. (Full dissipation of excessive pore water pressure. End of dissipation of excessive pore water pressure. End of consolidation)consolidation)

Sheeps Foot Roller or Static Sheeps Foot Roller or Static RollerRoller

Applies heavy load in a slow/rolling Applies heavy load in a slow/rolling action.action.

Used to compact cohesive soils in Used to compact cohesive soils in liftslifts

Consolidation of Granular Consolidation of Granular MaterialsMaterials

It is necessary to densify loose granular It is necessary to densify loose granular soils to achieve acceptable foundation soils to achieve acceptable foundation performance of structures.performance of structures.

Compaction of granular soils is achieved Compaction of granular soils is achieved by vibration:by vibration:

By use if a vibrator rollerBy use if a vibrator rollerBy frequent drops of a large mass from a great height By frequent drops of a large mass from a great height

(deep dynamic compaction). (deep dynamic compaction). By insertion of a large vibrating poker into the ground By insertion of a large vibrating poker into the ground

(vibro-compaction(vibro-compaction

““Vibratory Roller”Vibratory Roller”

Used to compact sand & gravelUsed to compact sand & gravel Delivers a dynamic blow as it rollsDelivers a dynamic blow as it rolls ““Shakes” particles into a more dense Shakes” particles into a more dense

configurationconfiguration

Vibro-CompactionVibro-Compaction

PenetrationPenetrationThe vibroprobe penetrates to the The vibroprobe penetrates to the required depth by vibration and required depth by vibration and jetting action of water and/or airjetting action of water and/or air

CompactionCompactionThe vibroprobe is retracted in 0.5 m The vibroprobe is retracted in 0.5 m intervals. The in situ sand or gravel intervals. The in situ sand or gravel is flowing towards the vibroprobe.is flowing towards the vibroprobe.

CompletionCompletionAfter compaction the platform needs After compaction the platform needs to be leveled and eventually roller to be leveled and eventually roller compacted at the surface. compacted at the surface.

The principle of sand compaction (Vibroflotation):The principle of sand compaction (Vibroflotation):

The compaction process consists of a flotation of the soil particles The compaction process consists of a flotation of the soil particles as a result of vibration, which then allows for a rearrangement of as a result of vibration, which then allows for a rearrangement of the particles into a denser state.the particles into a denser state.

Test PatternTest Pattern

Deep Dynamic CompactionDeep Dynamic Compaction

Natural soil deposits and undocumented fills can Natural soil deposits and undocumented fills can be densified by dropping large weights from great be densified by dropping large weights from great heights repeatedly on the ground surface. heights repeatedly on the ground surface.

The energy imparted is considerable & The energy imparted is considerable & compaction can be achieved at significant depths compaction can be achieved at significant depths below the ground surface.below the ground surface.

This mass of concrete, weighing about 12,000 pounds, was used for 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.deep dynamic compaction at the site of an oil storage tank in Japan.

Here the mass is lifted Here the mass is lifted to a height of 50 to a height of 50 feet and is ready to feet and is ready to be dropped. When it be dropped. When it hits the surface of hits the surface of the ground, the blow the ground, the blow will impart about will impart about 600,000 foot-pounds 600,000 foot-pounds

of energy.of energy.

These craters are the result of dropping the weight.These craters are the result of dropping the weight.

•The treatment pattern, energy level, number of passes and phasing of passes The treatment pattern, energy level, number of passes and phasing of passes are designed based on soil conditions, required bearing capacity and are designed based on soil conditions, required bearing capacity and

settlement characteristics. settlement characteristics.