ENVIRONMENTAL GEOMECHANICS CE-641 Department of Civil Engineering - - PowerPoint PPT Presentation

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IIT Bombay ENVIRONMENTAL GEOMECHANICS CE-641 Department of Civil Engineering DR. D. N. SINGH dns@civil.iitb.ac.in www.civil.iitb.ac.in/~dns IIT Bombay Slide 1 8.9.2009 Lecture No. 12

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SLIDE 1

ENVIRONMENTAL GEOMECHANICS CE-641 Department of Civil Engineering

  • DR. D. N. SINGH

dns@civil.iitb.ac.in www.civil.iitb.ac.in/~dns

IIT Bombay

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SLIDE 2

8.9.2009 Lecture No. 12 Lecture Name: Geomaterial Characterization

Sub-topics

  • Chemical characterization

pH, TDS, EC, BOD, COD Sulphite and Chloride contents Cation-Exchange Capacity Pore-solution sampling Corrosion potential Sorption-Desorption

  • Thermal Characterization
  • Electrical Characterization

IIT Bombay Slide 1 Environmental Geomechanics Lecture No. 12 D N Singh

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SLIDE 3

pH determination

Glass calomel electrode is used Soil solutions with different Liquid to solid ratios pH Temperature Total Dissolved Solids Electrical Conductivity Chemical Oxygen demand Biological Oxygen Demand

Environmental Geomechanics Lecture No. 12 D N Singh Slide 2 IIT Bombay

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SLIDE 4

IIT Bombay

The chloride and sulphite contents of the soils can be obtained

  • n an extract of 2:1 Liquid to solid ratio.

Indion Easy test kit (Ion Exchange, India Ltd.), an ion exchange resin, is employed A sort of a titration Change in color of the solution due to addition of chemicals

Chloride and Sulphite contents determination

Environmental Geomechanics Lecture No. 12 D N Singh Slide 3

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SLIDE 5

IIT Bombay Determination of Cation exchange capacity (CEC)

Is the amount of cations a soil can hold. Summation of exchangeable cations (Na+, K+, Ca+2 and Fe+3) Factors affecting CEC are: charge carrying capacity of the soil, pH, ionic strength of the pore-solution and presence of salts. Guidelines presented by IS 2720 (part XXIV, 1976) and (EPA SW-846) are followed for the determination of CEC of the soil sample. IS 2720 (Part XXIV 1976): The sample is first treated with hydrogen peroxide (H2O2), and boiled thoroughly for 1 h to remove organic contents. The treated sample is oven-dried and its 5 g is mixed with 50 ml 1N Sodium acetate (CH3COONa) solution with pH=5. This mixture is digested in a boiling water bath for 30 min., with intermittent stirring, and later centrifuged at a speed of 5000 to 6000 rpm, for 15 min. The supernatant liquid is discarded and the sample, settled at the bottom of the centrifuge tube is again treated with 50 ml of 1N CH3COONa solution (pH=5) and centrifuged. Repeat this process thrice, so as to ensure exchange

  • f Ca2+ in the soil by Na+, completely.

Environmental Geomechanics Lecture No. 12 D N Singh Slide 4

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SLIDE 6

IIT Bombay

This sample is treated with 1N Calcium chloride (CaCl2) solution and is again digested and centrifuged. This process is repeated thrice, so as to ensure exchange of Na+ by Ca2+. The sample is treated again with 50 ml 1N CH3COONa solution (pH=7) and again digested and centrifuged. This operation is performed thrice. The resulting supernatant from the last three steps is collected in a 250 ml volumetric flask, and the concentration of Ca2+ present in the solution is determined using the Atomic Absorption Spectrometer, AAS.

        × × × × × =

+ +

(g) soil

  • f

wt. 1000 cation the

  • f

weight Equivalent dilution (ml) extract

  • f

Vol. 100 g/ml) (

  • rNa

Ca

  • f

ion Concentrat ) (meq./100g CEC

2

µ

Minerals Present in soils(XRD) CEC (meq./100g) Montmorillonite 18.6 Kaolinite, Illite 4.989

Environmental Geomechanics Lecture No. 12 D N Singh Slide 5

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SLIDE 7

A Prerequisite to Soil-Water-Contaminant Interaction Studies To predict transport/fate of contaminants in the soil mass Design of suitable containment/Barrier system Assessment of safe waste disposal limits: Quantity & Concentration Leaching/Attenuation characteristics of soils Intrusion of pollutants in ground water resources Prediction of the loss of nutrients from the root zone Detection of the microbial activity in soils Validation of solute transport models

Slide 6

Pore-solution Sampling

The pore-solution sampling is identical to blood sampling

Environmental Geomechanics Lecture No. 12 D N Singh IIT Bombay

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SLIDE 8

In-situ (Field)

  • Lysimeter
  • Zero-tension Lysimeter
  • Tension Lysimeter
  • Soil Salinity Sensors
  • Absorption Techniques

Laboratory

  • Centrifugation
  • Pressure-membrane extractor (PME)

Sampling Techniques

Environmental Geomechanics Lecture No. 12 D N Singh Slide 7 IIT Bombay

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SLIDE 9

I n-situ studies

Objective: To simulate disposal facility in a Control Volume based on moisture movement concentration of contaminant(s)

Using a Lysimeter

A device which collects and senses percolating water through soil mass and helps in determining the Concentration of water soluble contaminant(s) As a function of time and space

Environmental Geomechanics Lecture No. 12 D N Singh Slide 8 IIT Bombay

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SLIDE 10

Lysimeter Studies

  • Simulate

the effect

  • f

percolating rainfall

  • n

the release

  • f

contaminants from waste froms

  • Provide insight in understanding the site as well as validating water

balance studies and radionuclide migration in the unsaturated zone

  • Data obtained from the study provide a link between the laboratory and

field conditions and thus aid in predicting radionuclide migration from shallow land disposal facility

Environmental Geomechanics Lecture No. 12 D N Singh Slide 9 IIT Bombay

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SLIDE 11

Lysimeter (Pore Solution Collection Device)

Collection device to Collection bottle Pervious fill Percolating water Soil Control volume

Environmental Geomechanics Lecture No. 12 D N Singh Slide 10

Zero Tension Lysimeter Collects Pore Solution From Saturated Soils

IIT Bombay

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SLIDE 12

Field Lysimeter

Waste rock material 485 mm 40 mm thick creek sand 50 mm thick Gravel (5-7 mm) 300 mm thick Gravel (14mm) Gravel (5-7 mm) To collect leachate Percolating water

Environmental Geomechanics Lecture No. 12 D N Singh Slide 11

Occurrence of preferential flow Influence of mobile colloids on contaminant mobility Extra organic matter in soil reduced colloid release

IIT Bombay

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SLIDE 13

Undisturbed soil core Sand Loose fill Sloping bottom A O A : Air inlet O : Pore solution extraction

Zero-tension Lysimeter

Environmental Geomechanics Lecture No. 12 D N Singh Slide 12 IIT Bombay

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SLIDE 14

Clay liner Granular Backfill Flexible membrane liner P P : Perforated pipe

  • To detect leakage from the clay liner
  • To determine in situ hydraulic conductivity of the liners
  • To demonstrate proper functioning of the clay liner

Environmental Geomechanics Lecture No. 12 D N Singh Slide 13

Collection Basin Lysimeter

IIT Bombay

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SLIDE 15
  • Performance assessment of solidified radioactive waste
  • Attenuation properties of soils

Upper compartment with fill material, sensors and moisture extraction cups Lower compartment for leachate collection

Environmental Geomechanics Lecture No. 12 D N Singh Slide 14

Validation of theoretical model by fitting Mathematical model to Lysimeter data

Basic Philosophy

Rain water Leachate

IIT Bombay

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SLIDE 16

Tension Lysimeter

Collects pore-solution from “Unsaturated Soils”

Environmental Geomechanics Lecture No. 12 D N Singh Slide 15

To Vacuum pump To sample bottle Ground Porous ceramic cup

PVC pipe

I I I – Inflow of pore solution under vacuum applied

IIT Bombay

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SLIDE 17

A Soil B To vacuum pump and collection bottle A – Porous plate B – Leachate collecting bottle Ground surface

Very preliminary design

Soil

Environmental Geomechanics Lecture No. 12 D N Singh Slide 16 IIT Bombay

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SLIDE 18

Soil Salinity Sensors

Used for in situ measurement of soil salinity Soil salinity is an indication of soil contamination

Environmental Geomechanics Lecture No. 12 D N Singh Slide 17

Absorption techniques

Sponge material as absorbent for sampling pore solution

  • Large surface area of the sponge improves sampling efficiency
  • Not a fully harnessed method

IIT Bombay

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SLIDE 19

Pore Solution Extraction by Centrifugation Laboratory technique

  • Soil sample mixed with immiscible liquid (CCl4)
  • Centrifuged in a tube at a particular rotational speed
  • Pore solution is displaced by CCl4
  • Pore solution could be extracted even from dry soils
  • Quantity of pore solution extracted depends on soil type
  • Results obtained cannot be generalized

Environmental Geomechanics Lecture No. 12 D N Singh Slide 18 IIT Bombay

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SLIDE 20

Importance of Lysimetric studies

  • Field studies

No control of boundary conditions, cost and time intensive

  • Laboratory studies

Cannot simulate field conditions, Spatial variability cannot be taken into account

  • Lysimetric study Intermittent approach

Simulates In-situ conditions with better control on boundary conditions

Lysimeter Device which creates a control volume of soil for studying various contaminant transport mechanisms under in-situ conditions Lysimeter identified as a potential tool for studying radioactive contaminant Interaction and migration in Geoenvironment

Environmental Geomechanics Lecture No. 12 D N Singh Slide 19 IIT Bombay

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SLIDE 21

R is the soil spiked (with Cs, Co & Tritium)

Environmental Geomechanics Lecture No. 12 D N Singh Slide 20 IIT Bombay

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SLIDE 22

Slurry of native soil

Environmental Geomechanics Lecture No. 12 D N Singh Slide 21 IIT Bombay

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SLIDE 23

Vial for pore-solution collection

Environmental Geomechanics Lecture No. 12 D N Singh Slide 22 IIT Bombay

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SLIDE 24

Details of the suction sampler

Stopper Sample Collector Flexible rubber tube To the vacuum Pump Ceramic thimble Perspex tube Soil slurry

Screw cap Environmental Geomechanics Lecture No. 12 D N Singh Slide 23 IIT Bombay

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SLIDE 25

Activities at a Glance

Environmental Geomechanics Lecture No. 12 D N Singh Slide 24 IIT Bombay

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SLIDE 26

TDR studies

200 180 160 140 120 100 80 60 40 20 0.0 0.1 0.2 0.3 0.4 0.5

θ

Depth(cm)

15/06/05 20/06/05 05/07/05 14/07/05 18/07/05 26/7 flash floods 26/08/05 27/09/05

GSL Hanumantha Rao, B, Sridhar, V., Rakesh, R.R., Singh, D.N., Narayan, P.K. and Wattal, P.K., “Application of In-situ Lysimetric Studies for Determining Soil Hydraulic Conductivity”, Geotechnical and Geological Engineering, 2009, DOI 10.1007/ s10706-009-9260-5. Published Online: 13 May 2009.

Environmental Geomechanics Lecture No. 12 D N Singh Slide 25 IIT Bombay

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SLIDE 27

Variation of 3H activity concentration with time in pore solutions in different Lysimeters at approx. 40 cm depth

  • 20

20 40 60 80 100 120 140 160 180 200

  • 100

100 200 200 300 400 400 500 600 600 700 800 800 900 1000 1000 1100 1200 1200 1300

3H Activity (Bq/ml) Time (days) Lysimeter 1 Lysimeter 2

Environmental Geomechanics Lecture No. 12 D N Singh Slide 26 IIT Bombay

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SLIDE 28

Variation of 137Cs and 60Co activity concentration with depth in dry soils after a period of 500 days

Environmental Geomechanics Lecture No. 12 D N Singh Slide 27 IIT Bombay

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SLIDE 29

Pressure Membrane Extractor

S PG PME A P PG C R RU B Air inlet Pressure gauge Drain Expelled water to the sampling bottle Air pressure

Environmental Geomechanics Lecture No. 12 D N Singh Slide 28 IIT Bombay