ENVIRONMENTAL GEOMECHANICS CE-641 Lecture No. 14 Prof. D N Singh - - PowerPoint PPT Presentation

ENVIRONMENTAL GEOMECHANICS

CE-641 Lecture No. 14

• Prof. D N Singh

Department of Civil Engineering

Sub-topics

• Chemical characterization

Pore-solution sampling Corrosion potential Sorption-Desorption

• Thermal Characterization
• Electrical Characterization
• Magnetic Characterization

25.09.2019 Lecture No. 14 Lecture Name: Geomaterial Characterization

Limitations Expensive instrumentation Cumbersome methodology Intensive & rigorous sample preparation, time consuming Complicated procedure for calibration and analysis Requirement of skilled and trained personnel Pore-solution extraction (PME) AAS ICP-MS Gas chromatography Ion selective electrodes Probes/Sensors Impedance spectroscopy (Impedance analyzer) Electrical resistivity methods Electro-magnetic methods (TDR/FDR: Time/Frequency domain Reflectometry) Dielectric constant (GPR: Ground penetrating radar) CHEMICAL CHARACTERIZATION

(In particular for ASSESSMENT OF SOIL CONTAMINATION)

Direct methods Indirect methods

PME: Pressure membrane extractor

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 Soil Salinity Sensors:

Chloride and Sulphite contents determination

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

Used for measuring soil suction and characterizing unsaturated soil

Soil Suction Matric(x) suction (soil matrix) Osmotic suction (salts)

Total Suction

Soil-water characteristic curve (SWCC)  w

AEV

wr

w : water content  : Soil suction

Exploring the possibility of WP4 (dewpoint potentiameter) AN INDIRECT METHODOLOGY FOR ASSESSING SOIL CONTAMINATION

Block chamber

Working principle of WP4

Measuring range- 0 to 80 MPa Works on relative humidity principle WP4 measures total suction of soil Uncontaminated soil : Total suction = Matric(x) suction Contaminated soil : Total suction = Matric(x) suction + Osmotic suction SWCC of uncontaminated and contaminated soil of same type would be different The difference between SWCCs would indicate soil contamination

A Case study

Soil used: Marine soil designated as contaminated soil (CS) Source: Collected from the coastal area of Mumbai, India

Soil property Value Specific gravity 2.64 Particle size characteristics Coarse sand (4.75-2.0 mm) 4 Medium sand (2.0-0.420 mm) 9 Fine sand (0.420-0.074mm) 11 Silt size (0.074-0.002 mm) 44 Clay size (< 0.002 mm) 32 Consistency limits Liquid limit (%) 61 Plastic limit (%) 37 Plasticity index (%) 24 Soil Classification (USCS) MH Oxide % by weight SiO2 33 Al2O3 11 Fe2O3 12 TiO2 2 CaO 6 Chlorides (ppm) 9840 Sulphites (ppm) 40 CEC (meq/100g) 4.04

Physical properties Chemical properties As such the soil is contaminated

Soil subjected to washing to nullify contamination

• No. of washings

LS Chloride (ppm) Sulphite (ppm) 1 2 6750 15 2 4 1850 10 3 6 800 10 4 8 250 5 5 10 90 < 5

1 2 3 4 5 6 7 10 20 30 40 50 60 70 80 90 100  (ms/cm)

• No. of washings

Washing nullifies contamination 10 10

1

10

2

10

3

10

4

10

5

10

6

10

7

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0  (kPa)

w

Contaminated soil Washed soil Difference due to contamination