problematic soils
DESCRIPTION
Environmental EngineeringTRANSCRIPT
Problematic Soil & Rocks • Some natural soil-rock inherits weakness from the parent material
such deposits include:
1. Shales & Weathered rocks 2. Residual soils3. Expansive clays4. Organic soils 5. Karst Region6. Loess 7. Dispersive clays8. Laterite soil9. Alluvial Sediments10. Saline & Alkaline soil11. Bentonite
Shale & Weathered Rocks• A fine-grained, sedimentary rock composed
of mud
• flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite are present
• Types of Shales :• Soil-like Shales: Bonding material is water
• Rock-like Shales: Particulate components are cemented together by calcareous, silicious, gypsiferous, phosphatic material
Shale & Weathered Rocks
• Characteristics –Porosity : 3 – 52 %Void Ratio: 0.03 -1.07Moisture Content : 5 -35 %Colour: Gray
Residual Soils
• Produced by in-situ decomposition of underlying rock & action of factors like microclimate, flora, fauna & geometric formations
• Breakdown is active in hot & humid regions of tropical climate – Because these are favorable conditions for chemical weathering
Residual soils
• Zones in Residual Soils :1. Upper layer – high degree of weathering
& removal of material2. Intermediate Layer – some degree of
weathering in top portions3. Bottom Layer – partially weathered zone
where there is a transition from weathered material to unweathered parent rock
Expansive Clays
• They exhibit greatest volume change from dry to wet state
• Possesses a considerable percentage of montmorillonite clay
• They do not have a continuous granular skeleton
Expansive Clays• Expansive clays are made up of small negatively
charged particles
• These clay particles attract water molecules, which are slightly polarized
• Montmorillonite clay have a very huge surface area
• This results in massive change in volume
Expansive Clays
• Mitigation Measures –Extend building foundations beneath the zone of
water content fluctuation zoneCollect surface runoff and to limit surface infiltration
during the rainy winter months Remove expansive soil & replace it with non-
expansive fillApplication of hydrated lime
Expansive Clays
• Black Cotton Soil –Found in central & southern IndiaColour: BlackExhibits excessive swelling & shrinkageDeep & wide cracksHighly problematic for foundations
Organic Soils
• Organic soils are those whose solid constituents consist predominantly of vegetable mater in various stages of decomposition
• Parent Material : Native Vegetation
• Form in wetlands
Organic soils
• Characteristics –Specific Gravity: 1.1 - 2.5 pH: Acidic - 4 to 7High void ratiosHighly compressible Do NOT receive proper compaction
Karst Region
• a geologic formation shaped by the dissolution of a layer or layers of soluble bedrock
• Most commonly develop on limestone, dolomite, gypsum formations
• Formation of Karst region takes thousands of years
Karst Region
• As rain water falls down, CO2 gets dissolved in it forming carbonic acid
H2O + CO2 → H2CO3
• As water moves underground, through tiny fractures in the limestone bedrocks, the rock slowly gets dissolved away by weak acids
Loess/Aeolian Deposits
• Sediment formed by the accumulation of wind-blown silt
• Loosely cemented by calcium carbonate
• Found in arid regions and deserts
• Loess mainly consists of quartz, feldspar and mica grains
Loess/Aeolian Deposits
• Characteristics –Homogeneous and porous structureAvg. particle size: 25 – 35 μmCarbonates : up to 15-18 %Quartz grains up to 70 %Colour : Yellowish or Brown
Dispersive Clays
• Dispersive soils are usually found in flood plains and lake bed deposits
• Soils often disperse when they are sodic
• These soils are highly erodible because of the low inter-particle attraction
Dispersive Clays
• Clay particles have a negative charge
• this charge is balanced by positively charged cations, such as Ca2+, Mg2+, K+ and Na+
• Dispersive soils contain large amount Na+ ions compared to other ions
• So the clay particles are less tightly bound to each other and the soil aggregates easily disperse
Laterite Soil
• Laterites are soil types rich in iron and aluminum
• formed in hot and humid tropical areas
• all laterite soils are red due to the presence of iron oxides
Alluvial Sediments
• Alluvial deposits loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting
• fine particles of silt and clay and larger particles of sand and gravel
Alkaline/Saline Soils
• Alkaline soils are soils with a high pH (> 9) and a poor soil structure and a low infiltration capacity.
• Found in North India & Central Europe
Alkaline/Saline Soils
• Causes –
1.Natural:the presence of soil minerals producing
sodium carbonate
2. Man – Made:the application of irrigation water (surface or
ground water) containing a relatively high proportion of sodium bicarbonates