Upload
imani12
View
224
Download
0
Embed Size (px)
Citation preview
8/8/2019 Group 1 Chemistry of Soils & Rocks
1/64
THE
CHEMISTRYOF
SOILS / ROCK
8/8/2019 Group 1 Chemistry of Soils & Rocks
2/64
PRESENTED BY
Ms. Uiras
Ms. Uiras
Mr. Nangolo
Mr. Nangolo
Ms Taapopi
Ms Taapopi
8/8/2019 Group 1 Chemistry of Soils & Rocks
3/64
1. Introductory Concepts
2.
Soil as a Construction Material3. Types of Soils in Namibia and their use in the
construction industry
4. Environmental chemistry of soils
SCOPE
8/8/2019 Group 1 Chemistry of Soils & Rocks
4/64
Soil and regolith
Soil-Forming Factors
Soil Components
Soil Properties and Chemistry
Chemical composition
Soil Profiles
Soil Classification
2. INTRODUCTION
8/8/2019 Group 1 Chemistry of Soils & Rocks
5/64
Soils are the main,
naturally occurringmaterials
Soil is found in the toplayer s of regolith
Regolith = soil +
portions of bedrock
In engineering, soil isreferred to as regolith :loose rock material or
layer coveringsolid/bedrock and iscreated by the action of
wind and water
Soil and Regolith
8/8/2019 Group 1 Chemistry of Soils & Rocks
6/64
y Geologic parent rock factor:Rocks are said to be the parent of soil because all soils originatedirectly or indirectly from them and are classified according totheir mode of formation. By a combination of physical andchemical processes rock masses are reduced to particles ranging
in sizes down to 0.001 mm.Soils result when collections of these particles are re-deposited,often in bodies of water, and are compressed and consolidated byfurther depositions
y Climatic - factor comprises of the meteorological conditionswhich surround the soil system such as temperature, rainfall,humidity ( the agents of weathering)
Soil Forming Factors
8/8/2019 Group 1 Chemistry of Soils & Rocks
7/64
y Topographic factor :
The general shape of the land surface in terms of its slopeand position relative to its geographic coordinates, affect the
moisture and temperature of the soil
Example Steep soils facing the sun are warmer, compared to thethose that dont. Steep soils erode and lose their topsoil as theyform and display different soils characters on both top and
bottom layers of the slope.
Precipitation has Significant impact on soil formation as itdetermines runoff water. Water erosion is more effective onsteeper, unvegetative slopes
Soil Forming Factors
8/8/2019 Group 1 Chemistry of Soils & Rocks
8/64
y Topographic factor :
Soil Forming Factors
8/8/2019 Group 1 Chemistry of Soils & Rocks
9/64
y Biological factor :
Decomposition of
Plants, animals with the
aid micro organisms
have an effect on the
formation of soil by
speeding up the rate of
dissolution of parent
material
Soil Forming Factors
8/8/2019 Group 1 Chemistry of Soils & Rocks
10/64
y Time factor :
Soil formation is an ongoing process. Over time soils shows
features that reflect the various forming factors.
Soil Forming Factors
8/8/2019 Group 1 Chemistry of Soils & Rocks
11/64
Soil forms from a
complex interaction
between earth
materials, climate andorganisms acting over
time , by the process of
weathering:
physical/mechanical
break down and
chemical alteration of
earth material
Soil developmemt
8/8/2019 Group 1 Chemistry of Soils & Rocks
12/64
y During the early stage of soildevelopment, soils are dominated bycharacteristics inherited from parentmaterial. Later on they show a changein their chemical characteristics.
8/8/2019 Group 1 Chemistry of Soils & Rocks
13/64
y During the early stage
of soil development,soils are dominated bycharacteristicsinherited from parentmaterial. Later on they
show a change in theirchemicalcharacteristics.
8/8/2019 Group 1 Chemistry of Soils & Rocks
14/64
Soils are a complex mixture of:
Inorganic Materials
Organic Matter
Soil Air
Soil Water
Soil Components
8/8/2019 Group 1 Chemistry of Soils & Rocks
15/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
16/64
Organic matter:
y 0.5 - 5% of soil volume
y made up of different substances that are
gradually broken down by microorganisms.y Includes carbohydrates, proteins, lignins, fats,
waxes.
Many of these compounds do not decomposecompletely and are transformed to humus,
8/8/2019 Group 1 Chemistry of Soils & Rocks
17/64
Soil Components
Soil Air
Air makes up approximately 25% of total soil volume.
8/8/2019 Group 1 Chemistry of Soils & Rocks
18/64
Soil Components
Soil Air
Soil is made up ofapproximately 40-60% ofpores. The pore sizeinfluences water holdingcapacity and aeration.
Porosity :Ratio of the volume of voids(containing air and/or water)in a soil to the total volumeof the soil expressed as a
percentage
Void ratio: is the ratio of thevolume of voids to thevolume of solid particles in
a soil
8/8/2019 Group 1 Chemistry of Soils & Rocks
19/64
Soil Components
Soil Water
Percolation:
Refers to the
downward f low ormovement of waterthrough the soilprofile
Capillary action :
The movement of aliquid along thesurface of a solid
caused by theattraction ofmolecules of theliquid to that of thesolids
8/8/2019 Group 1 Chemistry of Soils & Rocks
20/64
Soil Components
Soil Water
Eluviation: processof removingminerals from soil
with water
Illuviation: processof depositing theremoved minerals inunderlying layers
8/8/2019 Group 1 Chemistry of Soils & Rocks
21/64
Soil properties
Color
Red color results from leaching removal ofmaterials by dissolving them away from solids
8/8/2019 Group 1 Chemistry of Soils & Rocks
22/64
Soil properties
T
exture
clay
Silt
Sand
8/8/2019 Group 1 Chemistry of Soils & Rocks
23/64
Soil properties
T
exture
Unweathered primary materials:
have little capacity to hold water and nutrients and are
relatively chemically unreactive.
Gravel: 2 - 4mm
Sand: 0.05 - 2.0 mm
Silt: 0.002 - 0.05 mm
Weathered secondary materials:
Clay: is a secondary mineral less than 0.002 mm indiameter.
8/8/2019 Group 1 Chemistry of Soils & Rocks
24/64
Soil properties
T
exture
Textural classification:
y
Infiltration of water: rapid in sands, slow in clays.y Drainage: rapid in sands, slow in clays.
y Aeration: sand has rapid gas exchange; clay slow.
y Fertility: sand has low fertility, clay high, depending on type.
8/8/2019 Group 1 Chemistry of Soils & Rocks
25/64
Soil properties
Structure
8/8/2019 Group 1 Chemistry of Soils & Rocks
26/64
Soil properties
Moisture
Porous and Non Porous Soil: the rate of permeability
8/8/2019 Group 1 Chemistry of Soils & Rocks
27/64
Colloids:
y less than 0.1 micrometer(10-7 meters)
y clays + organic particles
y when mixed with waterform a suspension
y absorb water
Soil properties and Chemistry
8/8/2019 Group 1 Chemistry of Soils & Rocks
28/64
Soil properties and Chemistry
Acidity/Alkalinity:
8/8/2019 Group 1 Chemistry of Soils & Rocks
29/64
Clays: high cation exchange capacity (CEC) because they are
negatively charged and can attract, retain and exchange cations.
Their water holding capacity is very high because of their large
surface area per unit mass:
Ion Exchange:
Soil properties and Chemistry
y Three-layer clays: (Si-Al-Silattice) montmorillonite andillite have high CEC.
y
Two-layer clays: (Si-Al lattice)like kaolinite have low CEC.
y Amorphous clays: arecomposed of oxides of Fe and
Al and have very low CEC
8/8/2019 Group 1 Chemistry of Soils & Rocks
30/64
y oxygen (46.7%), silicon (27%), aluminium (8.1 %) and iron
(5.0%).y Ca, Mg, K, Na, P and S are present in the minerals and in the soil
solution.y Si, and Al occur as constituents of minerals and as oxides.y Fe occurs mainly in the form of oxides and ferromagnesium
minerals.y Ca occurs mainly in calcite, gypsum, apatite and dolomite.y Mg is present mainly in dolomite and hornblendey K occurs mainly in microcline and micay P occurs as aluminium phosphate and calcium phosphate and in
the organic form as phospholipids, inositol, choline, etc.y N occurs mainly in the organic form as proteins, amino acids,
etc.y All micronutrients like Mo, Fe, Mn, Zn, Cu, B occur in the
inorganic form.
Chemical composition of Soils
8/8/2019 Group 1 Chemistry of Soils & Rocks
31/64
Horizons specifically refer to
variations in soil profiles.
Soil Horizons (horizontal
layers)that exist within a vertical
column of soil
A coherent layer of soil, similar
in characteristics such as
composition, texture and color
that define the horizon fromother soil types, unique to
different geologic and climatic
areas
Soil Profile
8/8/2019 Group 1 Chemistry of Soils & Rocks
32/64
In order to understand relationships between different soils andto determine the usefulness of a soil for a particular use soils areclassified into categories
y Orders are the highest category of soil classification. Ordertypes end in the letters sol. In Namibia we use the WorldReference Base for soil Resources ( WRB)
Soil Classification
8/8/2019 Group 1 Chemistry of Soils & Rocks
33/64
2. SOIL AS A CONSTRUCTION MATERIAL
8/8/2019 Group 1 Chemistry of Soils & Rocks
34/64
History
Soil is the oldest construction and engineering material
& was used as the main element during construction
y Sumerian civilization : Ur ( 50th century B.C)
y Western civilizations: Rome ( 5th century B.C) and Greek (28th century B.C)
y African civilization: Nubian ( 2nd century B.C ) andEgyptians ( 3rd century B.C)
y Namibia : San people (7th century B.C)
8/8/2019 Group 1 Chemistry of Soils & Rocks
35/64
In engineering soil is mostly used in the following areas:
y As a Bearing capacity for the foundation of structures
y As a mixing agent to form concrete etc
y
As a stability slope
soil is one of the most complex fields in civil engineering tothe point that when it comes to the factor of safety in
design whatever has direct contact with soils, e.g.foundations, or soil based constructions, e.g.embankments, it has the highest number, i.e. theuncertainty in soil analysis and design is high. These mostlikely come from the way soil originates.
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
36/64
Effect of soil chemistry on structures: Concrete and Steel
y Ideally steels & concrete should be in the passive state in soils,but presence of water and aggressive chemicals like chloride
ions, sulphates, as well as types of bacteria, can cause localizedcorrosion.
Steel:The risk of corrosion, expressed as low, moderate, or high, is
based on soil drainage class, total acidity, electrical resistivitynear field capacity, and electrical conductivity of the saturationextract.. Steel installations that intersect soil boundaries or soillayers is more susceptible to corrosion than steel in installationsthat are entirely within one kind of soil or within one soil layer.
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
37/64
Concrete:
The risk of corrosion also is expressed as low, moderate, or high.It is based on soil texture, acidity, and amount of sulfates in thesaturation extract.
The factors contributing to Corrosion:
Soil Resistivity
y Indicator of soil corrosivity
y Corrosivity is associated with electrochemical reaction in soils,
y highly resistive soils slow down corrosion reactionsy Resistivity decreases with increase in moisture & chemical
concentration
y Well drained soils less corrosive
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
38/64
Acidity of the Soil
y Normal pH range of 4.5 8.0.
y As acidity increases so does the risk of corrosion
y Soil acidity is due to: mineral leaching, decomposition of acidicplants, industrial wastes, acid rain and certain forms of micro-
biological
Presence of Chlorides, Sulphates and Other Dissolved Species:
Most Important Factors
y
Cl-
ion concentrationCl- ion participates in pitting iniation of steel
presence decreases soil resitivity
presence due to: brackish groundwater, historical geologicalseabeds
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
39/64
y Soil moisture
contains sulphate ions, H+, HCO3-
sulphates less corrosive than Cl-
Risk: sulphates can be converted to highly corrosive sulphides by
reactions in soil
Microbiologically Induced Corrosion (MIC)
y
Corrosion induced by activities of microorganismsy Presence Sulphate Reducing Bacteria increases risk of corrosion
y By product of SRB metabolism = sulphide ions
y Sulphide ions react with metal surface
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
40/64
Oxygen concentration cellsy O2 takes part in cathodic reaction
y Supply of O2 changes with type of soil = creation of O2concentration cells
y
Increase in O2 concentration = increase in redox potential
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
41/64
y Acid chemically reacts with lime in concrete wearing awayat the structure, and exposing the aggregate.y Acid attacks steel leading to structural weakness and
failurey When acidic soils are exposed they will shrink and crack.This can result in subsidence and cracking of foundations
y As concrete surfaces deteriorates this leads to the corrosionof steel reinforcements
y Acidic soil => lack of vegetation => more rapid soil loss =>significant long term destruction of road structureShiftingor sinking of foundations may result in structural
cracking, damage or collapse.y Salt damage to roads and highways includes the
breakdown of concrete, bitumen and asphalt withassociated pot holing, cracking and crumbling of theroad base.
8/8/2019 Group 1 Chemistry of Soils & Rocks
42/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
43/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
44/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
45/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
46/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
47/64
y The major concern is to not allow excessive wateragainst the foundation. Wet alkaline soil willdamage concrete foundations and stucco siding.
8/8/2019 Group 1 Chemistry of Soils & Rocks
48/64
Mechanical properties:
y shear strength :
The internal resistance per unit area that the soil mass can offerto resist sliding failure along any plane inside it. Stresses inducedalong any plane in a soil mass can be converted to
- Normal stress : stresses perpendicular to the plane
- Shear stress : stresses along the plane
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
49/64
A
B
SOIL MASS
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
50/64
y Consolidation:
The ongoing removal, of water form the pores of saturatedcohesive materials with subsequent change in volume, bycontinued pressure.
When a load is applied to saturated clay the load is initiallycarried by the pore water, this load is gradually transferred to the
soil particles as the water is removed under pressure. Duringthese process settlement occurs, known as consolidationsettlement because of the reduction in volume associated withthe removal of water.
Settlement will continue to take place until excess pore pressure
has been dissipated. Depending on the permeability of clay andadjacent subsoil this process may occur over years. Before thefoundation is constructed the layer carries the normaloverburden load. After completion there is still some overburdenload plus the effect of pressure exerted by the foundation
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
51/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
52/64
y Permeability:
The capacity of a soil to allow water to pass through
y Effective stress :
The intergranular stress which exists between soil particles atany particular level in a soil mass
y Slope stability :
The assessment of the stability of earth slope against
failure, normally takes the form of a slip along one or moreruptured surfaces somewhere within the soil mass.
Soil as a Construction Material
8/8/2019 Group 1 Chemistry of Soils & Rocks
53/64
y Atterberg Limits
Liquid Limit, plastic limit, and shrinkage limit, related to
plasticity of a soil.
(Holtz and Kovacs, 1981)
LL
PI
HL
8/8/2019 Group 1 Chemistry of Soils & Rocks
54/64
3. TYPES OF SOILS IN NAMIBIA
CONSTRUCTION INDUSTRY
The most common soil types in Namibia are:
sandy soils (arenosols)young soil on solid rocks (leptosols)Fertile fluvisols
8/8/2019 Group 1 Chemistry of Soils & Rocks
55/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
56/64
y The most common soil types used inconstruction are shown in table below:
8/8/2019 Group 1 Chemistry of Soils & Rocks
57/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
58/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
59/64
8/8/2019 Group 1 Chemistry of Soils & Rocks
60/64
y Dune sands
Coastal sand dune systems are fragile, dynamic resources that
comprise only about two percent of Maines overall coastline.
8/8/2019 Group 1 Chemistry of Soils & Rocks
61/64
River sand
8/8/2019 Group 1 Chemistry of Soils & Rocks
62/64
Arenosols
8/8/2019 Group 1 Chemistry of Soils & Rocks
63/64
y A knowledge of environmental soil chemistry is paramountto predicting the fate, mobility and potential toxicity ofcontaminants in the environment. The vast majority ofenvironmental contaminants are initially released to thesoil. Once a chemical is exposed to the soil environment a
myriad of chemical reactions can occur that mayincrease/decrease a contaminants toxicity. These reactionsinclude adsorption/desorption, precipitation,polymerization, dissolution, complexation, andoxidation/reduction. These reactions are often disregardedby scientists and engineers involved with environmental
remediation. Understanding these processes will enable usto better predict the fate and toxicity of contaminants andwill ultimately provide us with the knowledge to developsound and cost-effective remediation strategies.
ENVIRONMENTAL SOIL CHEMISTRY
8/8/2019 Group 1 Chemistry of Soils & Rocks
64/64
END