chapter i. basic concepts
TRANSCRIPT
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CHAPTER I
BASIC CONCEPTS1.1 Definitions1.2 Generating agents
1.3 Types of soils and characteristics
1.4 Structure of clay minerals
1.5 Structure of soils
Professors: A.Zepeda y E Rojas
January 17, 2011
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1.1 DEFINITIONS
Soil
Soils are formed with sediments and other solid particles that can be
separated in single particles with the force of your hand when
saturated regardless of whether or not they have content of organic
matter (Karl Terzaghi).
Sediments are produced by mechanical break down or chemicaldecomposition of rocks.
Soil Mechanics.
Soil mechanics is the application of the laws of mechanics andhydraulics to engineering problems dealing with soils.
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People use the land to live on, and build all sort of structures:
houses, roads, bridges, etcetera. It is the task of the geotechnical
engineer to predict the behavior of the soil as a result of these
human activities.
The problems that arise are, for instance, the settlement of a
road or a railway under the influence of its own weight and the
traffic load, the margin of safety of an earth retaining structure(a dike, a quay wall or a sheet pile wall), the earth pressure
acting upon a tunnel or a sluice, or the allowable loads and the
settlements of the foundation of a building.
For all these problems soil mechanics provides the basic
knowledge.
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Soil mechanics is the science of equilibrium and motion of soil bodies. Here
soil is understood to be the weathered material in the upper layers of the
earthscrust.
The non-weathered material in this crust is denoted as rock, and itsmechanics is the discipline of rock mechanics.
In general the difference between soil and rock is roughly that in soils it is
possible to dig a trench with simple tools such as a shovel or even by hand.
In rock this is impossible, it must first be splintered with heavy equipmentsuch as a chisel, a hammer or a mechanical drilling device.
The natural weathering process on a mass of rock produced by rain, ice
wind, gravity and temperature gradually reduce the rock in smaller
particles. This process starts by the fracturing of rock bodies during the
freezing and thawing of the water inside the fissures in the rock.
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n
t
n
Real soils have two types of structures; a
macrostructure consisting of large particlesand large pores and a microstructure
composed by packets of very small pores.
1.4 Air, water and solid phases
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WATER IN THE SOIL
Soil grain
Adsorbed water
Gas (Air)
Capillary
waterSaturated soil
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air
water
soil
solids
Weigth
Wa0
Ww
Ws
Wm
Volume
Va
Vw
Vs
Vm
Vv
TRADITIONAL THREE
PHASES DIAGRAM FOR
SATURATED SOIL
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1.2 GENERATING AGENTS
The Earths crust is mainly attacked by air , water and temperature. Soils
are formed by the weathering of rocks and minerals. The surface rocks
break down into smaller pieces through a process of weathering
All attacking mechanisms can be divided in two groups:Mechanical disintegration (mechanical weathering) and
Chemical decomposition (chemical weathering).
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Mechanical weathering : Refers to the weathering of the rocks by physical
agents such as periodic changes of temperature, the freezing of water in
the joints and cracks in the rocks, effects of living organisms such as plants
or animals.
Because of these phenomena rocks degrade into sands, in extreme cases
can produce silts and rarely clay.
Chemical weathering (decomposition): The action of agents who attack
the rocks by modifying its mineralogical or chemical structure.The principal agent is the water and the most important attack
mechanisms are oxidation, hydration and carbonation.
Chemical effects of vegetation also have influence on the process of
weathering. These mechanisms generate clay as final product.
The formation of soils has occurred through the geological eras.
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1.3 TYPES OF SOILS
Residual and Transported Soils
Residual soils: The material attacked by weathering agents
remains in the same place, directly above their parent rock.
There is a number of important characteristics of the parent
rock inherited by residual soils. These are the weathering profile
and the set of structures such as fissures, failure planes and
joints.
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Transported soils: These soils are removed from the parent
rock by the weathering agents. Different deposits of transportedsoil can be found in the same horizon without a direct
relationship between them.
Transported soils show a number of important characteristics
such as the stratigraphic profile and the thickness of eachstratum. We can have several strata without direct relationship
among them.
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A Horizonor vertical washing area: is the mostsuperficial and it has roots and vegetation. Its
color is usually dark due to the abundance of
decomposed organic matter or humus,
determining the passage of water that drag
downward fragments of fine size and soluble
compounds. Highly leached materials (Lixiviation
or eluviation zone).
B Horizon or precipitation area: it lacks of
organic material, so its color is lighter, In the B
horizon materials drawn from above are
deposited, mainly clay materials, oxides and
metal hydroxides, carbonates, etc. (eIuviation
zone).C Horizon or parent rock: is made up to top of in
situ rocky material. Soil rests on horizon C, more
or less fragmented by mechanical and chemical
action, but it still recognizes it's original
characteristics.
Horizons of Soil.
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Transported Soils
There is a number of transport agents in nature, the
main ones are:
Glaciers
Wind
Rivers
FloodingsSeas
Gravity
These agents frequently work combined.
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Types of soil deposits
a)Glacial deposits
b) Moraine or Gravity deposits
c) Alluvial deposits
d) Fluvial deposits
e) Lacustrine deposits
f) Eolian deposits
g) Marine deposits
h) Organic Soil
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Western slopes of theSouthern Alps, South
Island, New Zealand
(G.R. Roberts, Nelson,
New Zealand).
Glacial deposits: The glaciers, in
their movement, generate big
pressures and abrasive effect on
rocks. The eroding action of the
glacial ice crushes and pulverizesthe parent bedrock and transforms it
into silt, sand, and gravel. This could
be accomplished due to the great
depths and enormous pressure of
glacier ice. There are several kinds
of glacial deposits, the main aremoraines.
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Moraine deposits
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A moraine
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The most recent glaciation on the North American continent
is the Laurentide (or Wisconsian) glaciation, which
dissappeared some 10 000 to 13 000 years ago.
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Fluvioglacial soil
Glacial deposits in the
Bicentenario Bridge,
Quertaro
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Gravity deposits: Moraine deposits, are sediments that accumulate at
the foot of mountain slopes because of avalanches, slides or instability of
the material on the slopes.
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Alluvium deposits: Sediment deposited by flowing water as in a flood plain
or delta. It is also called alluvium. Their grain size varies from large rock
fragments, gravel, sand, silt and some clay.
The term "alluvium" is not typically used in situations where the formation of
the sediment can clearly be attributed to another geologic process that is
well described. This includes (but is not limited to): lake sediments
(lacustrine), river sediments (fluvial), or glacially-derived sediments (glacial
till).
Alluvial plaine in Red Rock Canyon Park
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Alluvial Soil
Alluvial soil deposit in Quertaro
El t i i f
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Slickensides, the glossy (shiny and smooth) surfaces seen in
this picture are an obligatory requirement for vertisols
(USDA).
Electronic microscopy of sweep
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Picture of a soil layer in Bulgaria. There are carbonate
concretions.
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Fluvial Soil in a Delta
River deposits (fluvial): Coarse particles are graved dawn stream during
flooding and deposited when a decrease in the water velocity occurs. Fine
particles remain in suspension to be deposited in quieter waters. Thus, river
deposits are segregated according to size.
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The coarse stones that are created close to the mountains are
transported downstream by gravity water flow.
The stones are gradually reduced in size, so that the material becomes
finer: gravel, sand and eventually silt.
The material is deposited by flooding or flowing rivers. The coarsest
material at high velocities, but the finer material only at very small
velocities. This means that gravel will be found in the upper reaches ofa river bed, and finer material such as sand and silt in the lower
reaches (Arnold Verruijt, Delft University of Technology, 2001).
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Lacustrine material
Lacustrine deposits: Fine and very fine sediments like silts and clays are
deposited when running water comes to rest, like in lakes or deltas
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Wind deposit: Sand dunes in the Sahara, Morocco.
Wind deposits (Aeolin or Eolian): Loess and dune sands. This
sediments are typical of arid regions, and the water table is encountered at
great depth from the ground surface.
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Organic material
Marsh in Coatazacoalcos Ver.
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Marine soil
Marine deposits: They are related to the characteristics of the
rock formations eroded by sea water
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COARSE GRAINED SOIL MINERALS
Silicates of aluminium: Feldespar (of potassium,
sodium or calcium), micas, olivine and serpentine.
Oxides: Quartz, limonite, magnetite and corundum.
Carbonates: Calcite and dolomite.
Sulphates: Anhidrite and gypsum
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1.4 STRUCTURE OF CLAY MINERALS
Clay minerals are predominately hydrated silicates of aluminum and/or
iron and magnesium or other metals. These minerals are
predominantly crystalline in that the atoms composing them are
arranged in definite geometrical patterns.
Most of the clays minerals have sheet or layered structures.
Soil masses generally contain a mixture of several clay minerals.
Clay minerals are very small (less than 0.002 mm) and very
electrochemically active particles which can be seen using an electron
microscope.
There are two fundamental units (building blocks) for the clay mineral
structure:
Silica unit (Tetrahedron unit)
Aluminum unit (Octahedral unit)
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Oxygen
Silicon
Silica tetrahedron unit,
approximately 4.6 Ahigh
Block equivalent=
Angstrom unit A= 10-10m
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AluminumOxygen
Octahedral unit,
about 5.05 Ahigh
Octahedron
= Block equivalentG or B
G= Gibbsite (Al)
B= Brucite (Mg)
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According to the mineral structure of clay, some of the most common clay
minerals are the following
Kaolinite: Its structure is very stable in the presence of water.
Montmorillonite: Its structure is very unstable in the presence of
water. When the water content increases it swells.
Illite: Its behavior is intermediate between kaolinite and
montomorillonite
Kaolin is used in ceramics, medicine, coated paper, as a food additive,
in toothpaste, as a light diffusing material in white incandescent light
bulbs, and in cosmetics. It is generally the main component in porcelain.
Kaolin clay is widely used as an intestinal absorbent to combat intestinalinfections, in antidiarrheal medicines and for digestive disorders.
Kaolinite and halloysite clays are widely used for chinaware and
ceramic, due to absence of iron and subsequent iron decoloration at
high tempertures.
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7 ASi
Al
Kaolinite,
schema of the
basic unit
Al
Si
Si
Schema of the
Montmorillonite
9.6 A
Schema of the Illite
Al
Si
Si
10 A
K, Potassium
Angstrom unit A= 10-10m
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> 9.6
Cationes de cambio n H2O
Oxgeno
Hidroxilo, OH
Al, Fe, Mg
Si, a veces Al
Chemical structure of the montmorillonite
Oxygen
Silicon
Aluminium
Angstrom unit A= 10-10m
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agua capilar
agua
adsorbida
The phenomenon of capillarity in addition to the ionsin adsorbed water layer produce suction on
unsaturated soils (matric and osmotic suction).
Adsorbed
water
Capillary water
Clay particles
Negative electrical forces on the
surface of the mineral particles
attract water molecules and ions.
These forces decrease as the water
molecules and ions are farther
away from the surface of the grain.
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Floculated and dipersive clays depend on their mineralogy
and the environmental conditions in which they were formed
Distance
Attractio
n
Rep
ulsion
Floculated clay
Dispersive clay
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The specific surface is the sum of all the external area ofthe particles of soil per gram of material. A fine sand has
around 0.04 m2 of specific surface. A caolinite has 10 m2,
ilite has 100 m2 and montmorillonite has up to 800 m2.
The atoms of oxigen of the alluminate sheets are located atthe top and bottom of the clay particles in the illite and
montmorillonite. This produces a negative charge on the
flat surface of the particles.
Plasticity is the ability of soils to absorb water and todeform without fissuring. Clean sands have no plasticity
and montmorilonites are the most plastic of soils.
Specific surface and plasticity
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Water is strongly attracted by minerals. In the case of clays
plasticity is generated by the viscous water layer.
Coarse materials have much smaller specific surface andless affinity to water (the viscous layer is almost non
existent) and therefore do not develop significant
plasticity.
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Visc
osity
Distance from the particle surface, d
IIII II
-
-
-
-
-
-
-
-
-
-
-
-
-
--
+
+
Solid particle
Solid water layer (I)
Viscous water layer (II)
d
I
II
Free water (III)
The electromagnetic forces reduce as the molecules of water move away from the
surface of the clay particle
particle
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Cation Exchange Capacity (CEC)
Cations are positively charged ions.
Cation exchange capacity (CEC) represents the quantity of
negative charges existing on the surfaces of clay particles. The
negative charges attract the cations, hence the name cationexchange capacity.
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Diagram of a particle of clay with negative charges
on the surface attracting different cations.
Different types of clays have different CECs
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The most common soil cations, (including their chemical symbol and charge)
are: calcium (Ca++), magnesium (Mg++), potassium (K+), ammonium (NH4+),
hydrogen (H+), sodium (Na+), aluminum (Al+++), iron (Fe++), zinc (Zn++) and
copper (Cu++). Notice that some cations have more than one positive charge.
The capacity of the soil to hold on these cations is called the cation exchangecapacity (CEC).
The quantity of positively charged ions (cations) that a clay mineral or similar
material can accommodate on its negatively charged surface is expressed as
milliion equivalent per 100 g, or more commonly as milliequivalent (meq) per
100 g or cmol/kg.(10 cmolc/kg = 10 meq/100 g).
Clays are aluminosilicates in which some of the aluminum and silica ions
have been replaced by elements with different charge. For example,
aluminum (Al3+) may be replaced by iron (Fe2+) or magnesium (Mg2+), leading
to a net negative charge.
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The CEC of the soil will depend on the pH of the soil. A neutral soil (pH ~7)
will have a higher CEC than a soil with for example pH 5. Or in other words,the CEC of a soil with pH-dependent charge will increase with an increase in
pH.
This principle applies to increasing pH by the presence of lime for the
stabilization of expansive clays.
Expansive clayis a soil that is susceptible to large volume changes directlyrelated to changes in water content. Mitigation of the effects of expansive
clay on structures remains a major challenge in geotechnical engineering.
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Clay Exchange capacity, meq/100gr
Kaolinite 3-15
Halloysite 10-40
Illite 10-40
Vermiculite 100-150
Montmorillonite 80-150
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Identification of Clay Minerals
X Ray Diffraction: Each diffracted path is the image of different atomic
planes.
Electron microscope.
Differential Thermal Analysis (DTA): consists of simultaneously heating a
test sample and a thermally inert substance at constant rate (usually about
10C/min) to over 1000C and contiunuously measuring differences in
temperature between the sample and the inert material.
Chemical Analysis
Thermogravimetric Analysis
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x ray diffractometer . Equipped for qualitative and quantitative analysis of
crystalline compounds
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x ray difraction results
Difraction angle
Frequency
Al Mg Si
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Thermal analysis Temperature range is -100 to 1600C for simultaneous
DSC/DTA/TG, room temperature to 1600C for dilatometry
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TD
TD
Exothermic
Reaction
Endothermic
Reaction
Typical thermogram for soil minerals
a
a is the amplitude (cm);Ais the area (cm2)
A
1000C0
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Particle diameter (mm)
Gravel 4.75 76.2
Sand 0.075 4.75
Silt 0.005 0.075Clay 0.002 - 0.005
Colloid < 0.002Flat/Needle
Particles
Granular
Particles
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Shape of Granular Soil Particles
Angular: Short transported distance
Round: Large transported distance
ifi i f i i l
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Specific gravity of important minerals
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a) Soil Structure of coarse particles (simple structure): mainly
gravity forces are involved.
Assemblage of individual particles
Bulky particles
Dense Bulky SoilLoose Bulky Soil
Voids (Vv)
Bulky particle (Vs)
e=0.91 e=0.35
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Granular Loose Soil
Honeycomb soil structure
in granular soil
Loess (wind) deposit
Good compressive
Strength
Unstable if loaded
(collapse)
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Most soils contain a variety of particle sizes
Granular Soils Packing
In general, the greater the range of the size of soil
particles, the lower the void ratio because small particles
fill the voids of larger particles
Soil strength also depends on particle interlockGreater interlock higher shear strength
Interlock is a function of: particle shape and
amount of inter-particle contact
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Granular Soil Volumetric weigth
Very looseLoose
Mediun compact
Dense or compact
Very dense or very compact
High void ratio (e)Low strength, compressible
Low void ratio (e)
High strength, incompressible
Granular Dense Soil
Dense soil:
Low Vv, high Vs, therefore low e
Lower the soil void ratio the more dense,
Less settlement and higher strength
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minmax
max
ee
eeDr n
A measure of the structure of coarse soils is given by
the relative density parameter , Dr
minmax ,ee Are the laboratory values of themaximun and minimum void reatios
s
v
n
V
Ve Is the natural value of void reatio
The densest state, ,is obtained by vibrating a
confined weight of sand and measuring the volume.
The loosest state, is obtained by carefully placing
the material in a mould.
mine
maxe
Vv= volume of voids, Vs= volume of solids
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Flat clay particles
Flat thin particles of clays and colloids
cohesive soils
Large surface area with small mass
Specific surface = surface area/mass
Electrical forces dominate their behavior
Negligible gravity forces
Sand = 0.001 to 0.4 m2/gram
Silt = 0.4 to 1.0 m2/gram
Clay = 5 to 800 m2
/gram
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Dispersed
structure
d) Dispersed - particles repel each other
(negative to negative charge).
c) Flocculated clay or cardhouse structure: particles attract to each
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Plate particles: Flaky or mica shape
Edge to face contact. It is
called flocculated or
cardhouse strcture
Due to electrical forces and deposition in very low energy
environments, clays develop structures with large voids ratio
) y p
other in lakes or quiet rivers in edge to face contacts then settle
dawn due to gravity
Clay Structure
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a) Honeycomb structure: particles deposit due
to gravity forces. During this process they areattracted and attached to others
Clay Structure(particles equal or smaller than 0.002 mm in size).
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Floculated structure or superior order honeycomb
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b) Composite structure: Clay particles are aggregated or flocculated
together in submicroscopc fabrics units which are called domains. Domains
form groups called clusters and clusters form peds and group of peds of
macroscopic size.
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Composite structure
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Typical Kaolinite
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Electronic microscopy of sweep, natural soil
of Queretaro (Lpez-Lara, 2001).
Chemical analysis, Tejeda clay
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2.13Non soluble
material
0.06K2O
0.72Na2O
5.36MgO
66.52CaO
21.75%Lost by
calcination
3.663.94Potassium
1.791.79Sodium
35.6733.95Calcium
8.538.48Magnesium
Interchangeable cations
(meq/100g)
7.78.2Ph
48.86
me/100g
49.96
me/100g
Cation Exchange capacity
(CEC)
1.631.73Organic material
0.400.47MgO
1.131.36K2O
3.634.34CaO
6.716.74Fe2O3
19.9319.58AL2O3
55.76%54.13%SiO
21
SampleSubstance
Lime used in the
stabilization
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MONTMORILLONITE
2
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SILTSIZE FRACTION OF MEXICO CITY CLAY SHOWING FRAGMENTS OF SHELLS
(DIATOMS). (DIATOMSARE A MAJOR GROUP OF ALGAE MOST DIATOMSARE
UNICELLULAR, ALTHOUGH THEY CAN EXIST AS COLONIES).
20
Needle particles
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Halloysite nanotubes imaged at
Cornell University
A bundle of NaturalNanohalloysite nanotubes
compared to the width
of a human hair
Sensitivity and Thixotropic
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y p
Properties of Clays
Sensitivity, St: The ratio of peak undisturbedstrength to remolded
strength, as determined by unconfined compression test, was used
initially as a quantitative measure of sensitivity (Terzaghi, 1944).
St = qu/ qr
Thixotropy: Is defined as an isothermal, reversible, time- dependentprocess occurring in a material under conditions of constant volume
whereby it stiffens while at rest and softens or liquefies upon
remolding.
The remoulding of thixotropic clays causes an abrupt drop in pore
water tension (increase in pore water pressure) generating an
important reduction of its strength followed by a slow regain instrength during periods at rest.
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Thixotropic properties of clays
Strength
Time
Agedstrength
Remolded
Remolded
Remolded Strength
Sa
Sr
Sa/Sr = Thixotropic Strength Ratio
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Extremely sensitive clays losse
strength and become fluid when
remoulded. They are called quick
clays. (Photograph courtesy of
Haley and Aldrich, Inc.)
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St
Insensitive ~ 1.0
Slightly sensitive clays 1-2
Medium sensitive
clays
2-4
Very sensitive clays 4-8
Slightly quick clays 8-16
Medium quick clays 16-32
Very quick clays 32-64Extra quick clays >64
Classification of Sensitivity Values
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CAUSES OF SENSITYVITY
At least six differente phenomena may
contribuite to the develpment of sensitivity:
1. Metastable fabric;2. Cementation;
3. Weathering;
4. Thixotropic hardening;
5. Leaching, ion exchange;
6. Formation or addition of dispersing
agents.
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Honeycomb structure
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Colloidal particles: Grain size less than 0.0002 mm:If the colloidal particles are in a water suspension, there is
no effect of the gravity forces, they are in Brownian
movement, it is no possible the sedimentation. There is
repulsion force among the particles, caused by the negative
electrical charge on the surface of the grains.
Only with the addition of a electrolyte to the suspension for
neutralize the negative charge is possible the fluccullation
of particles and then the deposition
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Apparatus
Apparatus for DTA consists of a:
Sampler holder, usually ceramic, nickel, or platinum.
Furnace.
Temperature controller to provide a constant rate of heating.
Thermocouples for measurements of temperature and thedifference in temperature between the sample and the inert
reference material.
The recorder for the thermocouple output.
The amount of sample required is about 1 gr.
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Typical Kaolinite
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Element Weight% Atomic%
O K 14.83 26.83Na K 0.75 0.94
Mg K 2.25 2.68
Al K 2.75 2.95
Si K 46.61 48.04
K K 2.31 1.71
Ca K 5.01 3.62
Fe K 25.50 13.22
Totals 100.00
Spectrum processing:
Peaks possibly omitted: 2.149, 8.036, 8.475, 8.900, 9.706, 11.501, 13.367 keV
Processing option: All elements analyzed (Normalised)
Number of iterations = 2. Jurica Clay, Queretaro city. Mexico. Alicia Del Real L
JU100-2 sitio 1 espectro2
1 3 Characteristics and structure of soils
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1.3 Characteristics and structure of soilsMercury porosimeter measures pore size distribution in the range of pore diameters
between 300m and 3 nm. Samples can be in the form of granular powders or monoliths.
Nitrogen adsorption the pore size distributions in the range of pore diameters between 100
nm and 1.7 nm, the specific surface area, micropore volume and area, and total porevolume.
Mercury intrusion
Nitrogen adsorption
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Element Weight% Atomic%
O K 18.71 31.06
Na K 0.68 0.79
Mg K 1.75 1.92
Al K 10.36 10.20
Si K 46.95 44.40
K K 2.59 1.76
Ca K 4.57 3.03
Fe K 14.38 6.84
Totals 100.00
Spectrum processing :
Peaks possibly omitted : 2.149, 8.036, 8.515, 8.905, 9.706, 11.486, 13.350 keV
Processing option : All elements analyzed (Normalised)
Number of iterations = 3. Jurica Clay, Queretaro city. Mexico. Alicia Del Real L.
Sample: JU100 2 espectro4. Site of Interest 2 Type: Default. JU100-2 sitio 2
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Element Weight% Atomic%
O K 18.71 31.06
Na K 0.68 0.79
Mg K 1.75 1.92
Al K 10.36 10.20
Si K 46.95 44.40
K K 2.59 1.76
Ca K 4.57 3.03
Fe K 14.38 6.84
Totals 100.00
Spectrum processing :
Peaks possibly omitted : 2.149, 8.036, 8.515, 8.905, 9.706, 11.486, 13.350 keV
Processing option : All elements analyzed (Normalised)
Number of iterations = 3. Jurica Clay, Queretaro city. Mexico. Alicia Del Real L.
Sample: JU100 2 espectro4. Site of Interest 2 Type: Default. JU100-2 sitio 2
BENTONITE
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BENTONITE
Bentonite usually forms from weathering of volcanic ash, most often in the
presence of water. For industrial purposes, two main classes of bentonite exist:
sodium and calcium bentonite.
Sodium bentonite expands when wet, possibly absorbing several times its dry
mass in water. Because of its excellent properties it is often used in drilling mud
for oil and gas wells and for geotechnical and environmental investigations.
The property of swelling also makes sodium bentonite useful as a sealant,especially for the sealing of subsurface disposal systems for spent nuclear fuel
and for quarantining metal pollutants of groundwater. Similar uses include
making slurry walls, waterproofing of below-grade walls and forming other
impermeable barriers: e.g., to seal off the annulus of a water well, to plug old
wells, or as a liner in the base of landfills to prevent migration of leachate.
Sodium bentonite can also be "sandwiched" between synthetic materials tocreate geo-synthetic clay liners (GLC) for the aforementioned purposes. This
technique allows for more convenient transport and installation and it greatly
reduces the volume of sodium bentonite required.
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A slurry wallis a technique used to build reinforced-concrete walls
in areas of soft earth close to open water or with a high ground
water table.
A trench is excavated to create a form for each wall. The trench is
kept full of slurry at all times. The slurry prevents the trench from
collapsing by providing outward pressure which balances the
inward hydraulic forces and prevents water flow into the trench.Reinforcement is then lowered in and the trench is filled with
concrete, which displaces the slurry.
Slurry walls are typically constructed by starting with a set of guide
walls, typically 1 meter deep and 0.8 meter thick. The guide wallsare constructed on the ground surface to outline the desired slurry
trench and guide excavation.
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Slurry wall excavator
Excavation is done using a special clamshell-
shaped digger or a hydromill trench cutter.
The excavator digs down to the required
depth, or bedrock, for the first cut. Theexcavator is then lifted and moved along the
trench guide walls to continue the trench with
successive cuts as needed. The trench is kept
filled with slurry (usually a mixture of bentonite
and water) at all times to prevent collapse.
Once a particular length is reached, a
reinforcing cage is lowered into the slurry-
filled pit and then the pit is filled with concrete
from the bottom up using tremie pipes. The
concrete displaces the bentonite slurry, whichis pumped out and recycled.
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Schema of the process of building a Milan Wall: Excavation,
placement of joints between panels, placement of steel
reinforcement, filled with concrete from the bottom up using
tremie pipe.
Characteristics:
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Steel reinforcement for Milan Wall 27 m
deep, Metro, line B.Extraction of metalic joints.
Metro . Mexico City.
Characteristics:
Width: 60 cm (standard) 80 cm
Depth: up to 45 m
Mud: Bentontic polymer
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Completed Milan Walls.
Metro, Mexico City
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