Sub-topics Soil-water-Environment Interaction The Natural - - PowerPoint PPT Presentation

22.8.2013 Lecture No. 5 Lecture Name: Soil-Water-Environment Interaction

Sub-topics

• Soil-water-Environment Interaction
• The Natural Environment
• The Man-made Environment
• Response of the soil to the Environment
• Basic Concepts: Analysis of Gemoechanical Engg.

Problems

• Flaws in Classical Geomechanics

IIT Bombay Slide 1 Environmental Geomechanics Lecture No. 5 D N Singh

Soil-Water-Environment Interaction

The Natural Environment Geomicrobiosphere Man Made Environment The Particle Energy Field Theory Environmental Geotechnical Problems Understanding of Soil response to Environments (Short & long-term) Requires knowledge from other Disciplines

(Bacteriology/Biology, Chemical Engg./Climatology/ Geohydrology/Geophysics/Geochemistry/ Hydrogeology/Mechanics/Microgeology/Physico

• Chemistry/SoilScience/Soil

Engineering/Toxicology)

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 2

The Natural Environment

• Atmosphere (variable amount of vapour/dust)
• Biosphere (all plants & animal life)

Oxygen Cycle Nitrogen Cycle Carbon Cycle

• Hydrosphere (Water in oceans, rivers, lakes, aquifers, ice, clouds)
• Lithosphere (stone, rocks and soils)
• Geomicrobiosphere Ecosphere

(to study the characteristics of tree, vegetation, roots and bacterial activities in the soil and water and its overall response)

The Cycle of Nature

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 3

The Cycle of Nature

Oxygen Cycle (O2 is found in combination with Si & Al)

Alumino silicates, Metallic oxides, Carbonates, Sulfates, Nitrates, Phosphates)

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 4

Nitrogen Cycle (Transfer of Nitrogen between atmosphere, biosphere, lithosphere & hydrosphere in various forms)

Nitrogen fixation,

Carbon Cycle (oxidation of carbon containing material)

CO2 formation required for photosynthesis

Man-made Environment

• Agricultural wastes
• Human and Animal wastes
• Industrial wastes
• Mine wastes……Acid mine waste

(due to oxidation of Iron Sulphide (FeS2) or Pyrites to H2SO4)

• Nuclear wastes
• Construction Effects (Blasting/Dewatering/debris…)

Solid Liquid

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 5

Soil Response to Environments

• Soil structures (on/in/with)
• Pore fluid characteristics
• Soil-heat
• Soil-Chemical
• Soil Bacteria
• Soil-Root
• Soil-Electrical
• Soil-Liquid (water)

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 6

Pollution Processes & Soil-Pollution Interaction Land Pollution

Open dumps Chemical wastes Power plant wastes Septic tanks Chemicals in soil & food Erosion Agricultural manure Changes in: Hydraulic & Thermal conductivities Soil compaction Settlements Soil stability Seepage characteristics Corrosion

Water Pollution

Contaminated surface and ground water Chemical wastes Oil pollution Silt in water Nutrients in runoff Changes in:

• workability & Durability
• f concrete
• soil-water system
• Hydraulic conductivity
• Hydraulic structures

Air Pollution

Smoke & Odor Incineration Industrial gases Radiation Sewage odors Vehicle exhaust Pesticide sprays Dust Changes in: Accelearted weathering Corrosion of: bldgs./bridges/pavements Acid rains

Pollution Effect on Engineering Behavior

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 7

Basic concepts of Analysis

Most geotechnical projects occur in nature Long-term phenomenon Soil is more sensitive and susceptible to environment than any other construction material Loading may greatly affect soil properties (crushing) but not the only parameter to be considered Think of other factors: Heat Mositure (wet/Dry) Pollution intrusion

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 8

Classical Soil Mechanics: Some flaws

• 1. Specific gravity and Atterberg’s limits are constant
• 2. Void ratio and porosity as indicators of soil deformation
• 3. Water in the soil mass is mainly gravity water (need to

consider Environmental water & its solid and gaseous phases as well)

• 4. Flow through a soil mass is only due to hydrostatic potential

Water in soil responds to the imposition of any energy field and exhibits coupling affect(s) (need to consider thermal/electrical/magnetic/chemical effects) Flux Flux velocity

velocity= Coefficient of Energy Conductivity × Energy gradient

= Coefficient of Energy Conductivity × Energy gradient

• 5. Constitutive models are arbitrarily chosen.

Stress-strain relationship

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 9

IIT Bombay Environmental Geomechanics Lecture No. 5 D N Singh Slide 10

Major assumptions that deserve careful attention

• Constant seepage velocity
• Coupled flow process: (moisture and heat flow, Flow of

fines from the soil mass)

• Saturated versus unsaturated condition (causes of

creation of unsaturated state of the soil, characterization)

• Cation exchange capacity (CEC) of geomaterials

and its effect on soil-contaminant interaction

• Bio- / Chemico- degradation of geomaterials (mainly

Organic soils) due to prolonged exposure to man-made environment

Soil Classification: Is this Acceptable

• Grain-size distribution
• Soil Consistency (moisture content)
• LL
• PL
• PI

Present scenario (Parameters) Proposed scenario (Parameters)

• % Passing #200 Sieve
• Specific surface
• pore fluid characteristics (pH)
• Ion-exchange capacity (CEC)
• Sorption Characteristics

(Absorption & adsorption)

• Electrical properties (Conductivity &

Dielectric constant

• Thermal diffusivity, resistivity, heat

capacity

Environmental Geomechanics Lecture No. 5 D N Singh Slide 11 IIT Bombay