SLIDE 1 Sub-topics
- Chemical characterization
Pore-solution sampling Corrosion potential Sorption-Desorption
- Thermal Characterization
- Electrical Characterization
05.10.2018 Lecture No. 18 Lecture Name: Geomaterial Characterization
SLIDE 2
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
Pore-solution Sampling
The pore-solution sampling is identical to blood sampling
SLIDE 3 In-situ (Field)
- Lysimeter
- Zero-tension Lysimeter
- Tension Lysimeter
- Soil Salinity Sensors
- Absorption Techniques
Laboratory
- Centrifugation
- Pressure-membrane extractor (PME)
Sampling Techniques
SLIDE 4 Importance of Lysimetric studies
No control of boundary conditions, cost and time intensive
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
SLIDE 5
R is the soil spiked (with Cs, Co & Tritium)
SLIDE 6
Slurry of native soil
SLIDE 7
Vial for pore-solution collection
SLIDE 8 Details of the suction sampler
Stopper Sample Collector Flexible rubber tube To the vacuum Pump Ceramic thimble Perspex tube Soil slurry
Screw cap
SLIDE 9
Activities at a Glance
SLIDE 10 TDR studies
200 180 160 140 120 100 80 60 40 20 0.0 0.1 0.2 0.3 0.4 0.5
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.
SLIDE 11
Variation of 137Cs and 60Co activity concentration with depth in dry soils after a period of 500 days
SLIDE 12 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
SLIDE 13
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/Analysis (PME) AAS ICP-MS Gas chromatography Ion selective electrodes Impedance spectroscopy (Impedance analyzer) Electrical resistivity methods (Probes) Electro-magnetic methods (Time domain Reflectometry) Dielectric constant (Ground penetrating radar) CHEMICAL CHARACTERIZATION for ASSESSING SOIL CONTAMINATION
Direct methods Indirect methods
SLIDE 14 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
SLIDE 15
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
SLIDE 16 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
SLIDE 17 Soil subjected to washing to nullify contamination
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)
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
SLIDE 18
For geotechnical engineers, it’s very important subject Metal corrosion in undisturbed soils is generally very low regardless of the soil composition (e.g. metal piles, reinforcement of foundation etc.) Corrosion of metal (steel) in disturbed soils (e.g., buried pipelines that are backfilled) is strongly affected by soil conditions & properties. Soil changes its chemical and physical nature continuously over time and seasonally.
Corrosion Potential of Soils
Pipeline damage from pitting/corrosion
SLIDE 19
- Chloride content
- Moisture content
- Oxygen content/Redox potential
- Soil permeability/texture
- pH/Acidity
- Temperature
- Soil resistivity
- Drainage characteristics
- Sulfate/Sulfite ion concentrations
- Microbiological activity
- Stray currents (from cathodic protection, DC traction
system viz., train, metro)
- Spillage of corrosive substance/pollution
Soil Characteristics & Environmental Variables
SLIDE 20
Clay in the soil mass reduces movement of air (oxygen) and water, i.e. low aeration, when wet, and hence increase in local (pitting) corrosion. High plasticity of clay (swelling/shrinking soils) can pull off susceptible coatings on the structures. Clay is susceptible to cracking (during wetting-drying cycles) which helps transport of air and moisture to the structures buried in it. Sand promotes aeration and moisture distribution & hence, soluble salts and gases (air/oxygen) are easily transported to structures, causing greater general corrosion but less pitting.
Soil Classification/Texture
SLIDE 21
Bored Cast in-situ piles
Reinforcement in concrete pile exposed due to leaching of concrete Chloride and Sulphate content of water found well within prescribed limit & hence water not corrosive. Ryzner index (RI) of water was found out to be 7.7 & hence water is corrosive and unsaturated
SLIDE 22
pH scale for Soils
Langelier Saturation Index (LI)
Determines if calcium carbonate will precipitate or not LI = pH – pHs pH = actual pH value measured in the water pHs = pH of the water in equilibrium with solid CaCO3 If LI > 0 calcium carbonate will precipitate If LI < 0 calcium carbonate won’t precipitate The CaCO3 layer deposited on surfaces acts as a protective coating.
Ryznar Index
Determines the degree of scale formation RI = 2 pHs – pH RI < 5.5 heavy scale will form 5.5 < RI < 6.2 scale will form 6.8 < RI < 8.5 water is corrosive RI > 8.5 water is very corrosive
SLIDE 23 ASSESSMENT OF CORROSION POTENTIAL OF SOILS
Durability of underground structures is seriously affected by corrosion of the concrete (IS: 456-2000) Specifications for type of cement, minimum cement content, maximum water-cement ratio, etc., to be adopted stringently, based on the exposure
- f the concrete to different concentrations of sulphates in the soil or
ground water. However, for assessment of corrosion potential of underground structures, chemical properties of the soil need to be considered in details. Corrosion is an electrochemical process Certain conditions must exist for the corrosion to occur (corrosion cell)
Effects of soil characteristics on corrosion By Victor Chaker, J. David Palmer ASTM Committee G-1 on Corrosion of Metals
SLIDE 24 Soil (Electrolyte) Metallic connection Anode Cathode Electric current
Electrochemical reaction
Corrosion
The “Corrosion cell”
Soil Electrolyte
Therefore properties of soils play a crucial role in accelerating corrosion.
Properties of soils:
Electrical resistivity pH moisture content Porosity sulphate and chlorides content redox potential presence of micro-organism temperature are important for evaluating the corrosion potential of soils (DIN 50929-3). For corrosion, the elements that are soluble in water are important: – Base forming: Na, K, Ca, Mg (raise pH). – Acid forming: Carbonate, Bicarbonate, Chloride ion, Nitrate, and Sulfate (lower pH).
SLIDE 25
Rating based on the soil fraction Rating based on the electrical resistivity Rating based on the pH Rating Based on the ground water status Rating based on the sulphite content Rating based on the chloride content
Based on different soil characteristics, a certain rating (R1 to R6) for the soils has been assigned and the sum of these ratings is a measure of the overall soil corrosivity.
SLIDE 26 Rating based on the soil fraction
Soil fraction % by weight R1 Clay & silt <10 +4 10 to 30 +2 30 to 50 50 to 80
>80
Organic matter, e.g.: muddy or swampy soils: peat, mud, marsh >5
Severely polluted: due to fuel ash, slag coal, coke, refuse, rubbish or waste water
Rating based on the electrical resistivity Resistivity (.m) R2 >500 +4 200 to 500 +2 50 to 200 20 to 50
10 to 20
<10
Rating based on the pH PH R3 >9 +2 5.5 to 9 4.0 to 5.5
<4
Higher conductivity: high corrosion rate (efficient electrolyte)
SLIDE 27 Rating Based on the ground water status Ground water status R4 No groundwater Groundwater
Groundwater at times
Rating based on the sulphite content Sulphite content (g/l) R5 <0.15 0.15 to 1
1 to 2
>2
Rating based on the chloride content Chloride content (ppm) R6 <100 100-2000
2000-10000
>10000
Total assessment of the corrosion potential Summation of R1- R6 R Corrosion potential 0 Virtually not corrosive
Slightly corrosive
Corrosive < -10 Highly corrosive
Chloride ions: Cause pitting of steel and decrease soil resistivity.
