The document discusses the physical properties of rocks and soils that are important for civil engineering projects. It describes measuring properties like unit weight, density, porosity, strength, and permeability. It then discusses specific gravity determination and how porosity is measured. Various stress types on rocks, including compressive and tensile strength, are defined. Methods for determining rock properties like point load index and Schmidt hammer rebound number are presented. The document also covers rock mass classification systems and significance of faults and folds for engineering projects, as well as weathering and alteration of rocks.
2. PHYSICAL PROPERTIES OF ROCKS AND
SOILS (INDEX PROPERTIES)
For civil engineering design, it is necessary to assign
physical properties to each unit of soil or rock within a
ground model.
These include readily measurable or estimated attributes
such as unit weight, density and porosity.
Other parameters that are often needed are strength,
deformability and permeability. In the case of
aggregates (rock used in construction for making
concrete) and for armourstone, important attributes are
durability and chemical stability.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 2
3. WEIGHT, POROSITY AND SORPTION
In dealing with any material, it is necessary to know its weight as expressed in
pounds per cubic foot or tons per cubic meter.
The unit weight of a rock depends on the specific gravity (density) of its
constituents, on its porosity and on the amount of water in the pores.
Specific gravity may be determined in the laboratory as follows
1.The rock specimen is dried for 24 hrs in an oven at 105°C, cooled and weighed
(Wo)
2.It is then completely immersed in water for 48hrs and weighed in saturated
condition (Ww)
3.Then the specific gravity 𝐺 = 𝑊𝑜 ÷ 𝑊 𝑤
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5. WEIGHT, POROSITY AND SORPTION
Porosity is a measure of the volume of voids in a
material or mass. In materials porosity depends upon the
space between grains; in masses it would also include any
space provided by open fissures and joints.
Intergranular porosity is often determined in the
laboratory by comparison between dry and saturated
weights of the sample.
To become fully saturated, voids must be in contact, and
both interconnections and voids must be large enough to
allow the flow of water under reasonable pressures.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 5
6. WEIGHT, POROSITY AND SORPTION
One or both of these conditions is often not
satisfied, particularly for fine grained materials, and
the results of such tests are properly described as
apparent porosity.
There are some porous rocks, such as vesicular
basalts, that are porous but whose porosity cannot
be measured by conventional means because the
voids are not in contact i.e. the material is
impermeable.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 6
7. MATERIAL V/S MASS
Most tests and measurements are made on small-scale samples in
the field or the laboratory and need to be scaled up according to
theoretical or empirical rules, to include for geological variability,
fabric and structure.
For example, a soil mass might be made up of a mixture of
strong boulders in a matrix of weak, soil-like material, and this
mix has to be accounted for in assigning parameters for
engineering design.
Mass strength, deformability and permeability of rock
masses are controlled largely by the fracture network, rather than
intact rock properties; the permeability of intact rock might be
10−11 m/sec, which could be thousands of times lower than for the
fractured rock mass.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 8
8. ORIGINS OF PROPERTIES
The strength of soil and rock (geomaterials) is derived from
friction between individual grains, from cohesion derived from
cementation filling pore spaces and from inter-granular bonds such
as those formed by pressure solution (Tada & Siever, 1989).
The strength and deformability of soil is also a function of the
closeness of packing of the mineral grains.
Densely packed soil will be forced to dilate (open up) during shear at
relatively low confining stresses as the grains override one another and
deform, and the work done against dilation provides additional strength.
The same principles apply to rough rock joints or fractured rock
masses.
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9. ORIGINS OF PROPERTIES
Different minerals may also have fundamentally
different properties – some are more chemically
reactive and may form strong chemical bonds in the
short term, some are readily crushed or scratched,
whilst others are highly resistant to damage or
chemical attack.
Some, such as talc and chlorite, are decidedly
slippery and if present on rock joints can result in
instability.
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10. EXAMPLE
This picture shows a graded series of
sediments.
The sand horizons become finer upwards, as
is typical of sediments deposited from a river
into a lake.
At the top of the sample, there is a second
sand horizon that has been deposited onto the
underlying sediment.
This has deformed the underlying sediments,
producing a loading structure, which shows
that the soil was in a very soft state at the time
of formation.
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11. EXAMPLE
Contrast this with the rear of the
same sample showing conchoidal
fractures in what is actually
extremely strong rock.
The conversion from soft mud to
rock has occurred over a long time
but has occurred naturally and, in
practical geotechnical engineering,
we encounter and need to deal with
the full range of materials,
transitional between these end
members.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 12
12. STRESSES IN ROCK:
COMPRESSIVE STRENGTH
Generally 3 kinds of stresses are considered in
studying the resistivity of the rock: compressive
stresses which try to decrease the volume of the
material; shear stresses which tend to move one
part of the specimen with respect to other or make it
flow; and tensile stresses which tend to produce
cracks and fissures in the material.
Stresses are measures in pounds per square foot or
pounds per square inch.
Compressive strength of a material such
as rock, is the stress required to break a
loaded sample that is unconfined at the
sides.
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13. Here the load tending to break the
sample is designated as P.
If the cross section of the sample is
2inch by 2inch and the compressive
strength of the rock is 10000 psi, a load
of 10000 x 4 = 40,000 lbs will break the
sample.
Hence the formula goes this way
P (psi) =
𝑃
𝐴
P = lbs and A = square inch
STRESSES IN ROCK:
COMPRESSIVE STRENGTH
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14. STRESSES IN ROCK: COMPRESSIVE
STRENGTH
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15. STRESSES IN ROCK: TENSILE
STRENGTHThe tensile strength of granite is about
1000 psi, only a fraction of its
compressive strength.
Other rocks like marble has lower
tensile strengths of 700 to 900 psi,
limestone about 500 psi and sandstone
100-200 psi.
If a stone slab is placed on practically
immovable supports and subjected to the
action as a load P the slab deflects and
there is tension at the bottom of the slab
and compression at the top.
If the load P is gradually increased, the
slab fails by tension. R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 16
16. POINT LOAD INDEX
For a point load test, a compressive load is applied through two
conical platens, which causes the rock to break in tension between
these two points.
If the breaking load is P, the point load index, Is, can then be
determined by
𝐼 𝑠 =
𝑃
𝐷2
where D is the diameter of the specimen if the load is applied in
the diametric direction of a core. In other cases, 𝐷 = 2 𝐴/π, where A
is the minimum cross-sectional area of the specimen for a plane
through the platen contact points.
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19. SCHMIDT HAMMER REBOUND NUMBER
The hammer measures the rebound of a spring-loaded mass impacting
against the surface of the sample. The test hammer will hit the concrete at a
defined energy. Its rebound is dependent on the hardness of the concrete and
is measured by the test equipment. By reference to the conversion chart, the
rebound value can be used to determine the compressive strength
The Schmidt rebound hammer has been used for testing the quality
of concretes and rocks.
Schmidt hammers are designed in different levels of impact energy,
but the types of L and N are commonly adopted for rock property
determinations.
The L-type has an impact energy of 0.735 Nm which is only one
third that of the N-type. R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 20
22. ROCK MASS CLASSIFICATION
Historically, rock-mass classification has been based on
percent core recovery, which is severely limited in value.
Core recovery depends on many factors including
equipment used, operational techniques, and rock quality, and
provides no direct information on hardness, weathering, and
defects.
Even good core recovery cannot provide information
equivalent to that obtained by field examination of large
exposures, although ideal situations combine core recovery
with exposure examinations.
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27. SIGNIFICANCE OF FAULTS AND FOLDS
IN ENGINEERING
Fractures in rock masses accompanied by differential displacements
on both sides of the fracture often cut a site irrespective of the dip and
strike of the rock.
Search for faults is not always effective, they might be discovered
later.
Faults may be deeply buried, and if the excavation floor is intercepted
by small faults containing gouge and brecciated rock, in many cases it
is advisable from both technical and economic viewpoints to abandon
the site.
In other cases, if a fault is disclosed when the bottom of the
excavation has almost reached the design elevation, the site may be
made usable by removing a large portion of faulted rock, increasing the
cost of both earth and concrete work. R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 30
28. SIGNIFICANCE OF FAULTS AND FOLDS
IN ENGINEERING
From the basic products of faulting, gouge is probably the most
concern in foundation problems.
1. This is usually an impervious material and may hinder or stop
the movement of GW and thus create disastrous hydrostatic
heads e.g. if encountered in tunnel.
2. Also it may reduce the coefficient of sliding friction along the
fault plane; thus any heavy load (e.g. building) placed upon
beds overlying a gouge seam may start translating laterally,
ultimately causing failure.
3. The presence of soft breccia may cause sudden “squeezes” in a
tunnel that intersects a fault.
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29. SIGNIFICANCE OF FAULTS AND FOLDS
IN ENGINEERING
“active”, “inactive” and “passive” faults need to be identified.
Active faults are those in which movements have occurred during the
recorded history of man and along which further movements can be
expected at any time.
Inactive or passive faults are ruptures that have no recorded history of
movement and thus are assumed to be and probably will remain in
static condition.
Unfortunately it is impossible to state definitely if an apparently
inactive fault will remain in that condition.
The fault may reopen either because of a new strain accumulation in
the locality or from the effect of earthquake vibrations.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 32
30. SIGNIFICANCE OF FAULTS AND FOLDS
IN ENGINEERING
Of the various types of folds, the synclines are perhaps the most
significant in engineering because of their capacity to convey and
accumulate fluids.
Serious water problems may arise in the construction and
maintenance of tunnels intersecting synclines containing water-
bearing strata.
If such a syncline is discovered before the design period, the
elevation of the planned tunnel may be changed inorder to place it
in the drier strata.
In foundations proper, folds are no so critical as faults.
Occassionally, the folds may influence the selection of a damsite.
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31. ALTERATION OF ROCK
Various rock types decompose to characteristic soil types.
The type of residual soil (active to inactive) and the
approximate depth to fresh rock at a given location are
generally predictable if the climate, topography, and basic rock
type are known and the processes of rock alteration are
understood.
Alteration refers to any physical or chemical change in a rock
or mineral subsequent to its formation (Rice, 1954).
Weathered rock has undergone physical and chemical
changes due to atmospheric agents.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 34
32. ALTERATION OF ROCK
Disintegration refers to the breaking of rock into smaller
fragments, which still retain the identity of the parent rock,
through the action of physical agents (wind, water, ice, etc.).
Decomposition refers to the process of destroying the identity
of mineral particles and changing them into new compounds
through the activity of chemical agents.
Hydrothermal alteration refers to changes in rock
minerals occurring deep beneath the surface, caused by
percolating waters and high temperatures.
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33. WEATHERING AGENTS AND
PROCESSES
Mechanical Fragmentation
Mechanical fragmentation is a product of rock joints forced open and fractured under the
influence of freezing water, growing tree roots, and expanding minerals; slabs freed by
exfoliation and stress relief; and blowing sand causing erosion and abrasion. Talus is the
accumulation along a slope of large fragments that have broken free and migrated downward.
Chemical Decomposition
Chemical decomposition occurs through the processes of oxidation, leaching, hydrolysis,
and reduction. From the engineering viewpoint, it is the most important aspect of rock
alteration since the result is residual soils.
Hydrothermal Alteration
Occurring deep beneath the surface at temperatures of 100 to 500°C, hydrothermal
alteration changes rock minerals and fabrics, producing weak conditions in otherwise sound
rock. It is particularly significant in deep mining and tunneling operations.
Argillization is the most significant of many forms of hydrothermal alteration from the
point of view of construction, since it represents the conversion of sound rock to clay.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 36
35. Formation of weathering
mantle in tectonically stable
areas. (From Morin, W. J. and
Tudor, P. C., AID/Csd
3682, U.S. Agency for
International Development,
Washington, DC, 1976. With
permission.)
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38. FINAL PRODUCT AND THICKNESS
The final product is usually a mixture of quartz particles
(which are relatively stable), iron oxides, and clay minerals.
Vermiculite and chlorite are uncommon since they alter readily
to montmorillonite, illite, and kaolinite. The clay minerals result
from the most common groups of silicates (feldspars and
ferromagnesians).
The ferromagnesians usually contain iron, which decomposes to
form iron oxides that impart a reddish color typical of many
residual soils.
The thickness of the decomposed zone is related directly to rock
type in a given climate as well as to topography.
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39. The greatest depths of decomposition occur in tectonically stable areas. In unstable tectonic areas,
the weathered zone is thinner because topographic changes increase the erosion activity.
Glaciation removes decomposed materials, often leaving a fresh rock surface.
In glaciated areas, the geologic time span for decomposition has been relatively short, and the
depth of weathering is shallow.
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40. FINAL PRODUCT AND THICKNESS
It is the partially saturated zones where vertical water movement can occur that provide the
optimum conditions for oxidation, reduction, and leaching, and where decomposition is most
active.
Decomposition depth, often to depths in excess of 100 ft, is greatest beneath the crests of the hills
composed of foliated crystalline rocks.
Along the sideslopes, where erosion occurs, the depth is about 30 ft. In the narrow valleys, where
rock is permanently saturated, the decomposed depth is usually only of the order of 10 ft at the
most, and streams often flow on fresh rock surfaces.
There is little decomposition activity below the permanent water table. Limestone cavities do
not increase substantially in size unless water is caused to flow.R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 44
41. FINAL PRODUCT AND THICKNESS
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45. WEATHERING PROFILE IN IGNEOUS
ROCKS
Quartz-rich sialic rocks undergo 4 stages of weathering development
Stage 1 : Weathering proceeds first along the joints of the fresh rock surface, and
decomposition is most rapid where the joints are closely spaced. The granite begins to alter in
appearance; the biotite tends to bleach and lighten in color, and iron compounds migrate,
staining the rock yellowish-red to reddish-brown.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 49
46. Stage 2 : During intermediate decomposition, the granite loses its
coherence and becomes crumbly. In humid climates, a sandy matrix forms
around spherical boulders (corestones), especially in partially saturated but
continuously moist zones.
The corestone size reflects the fracture spacing. In well-drained zones,
Stage 2 soil cover is often relatively thin, and on steep slopes in granite the
soil is removed quickly, and slabbing by exfoliation occurs.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 50
47. Stage 3 : During final decomposition, a sandy soil is formed,
composed chiefly of angu lar particles of quartz and feldspar. Further
decomposition yields clayey soils (Grim, 1962). The presence of
“corestones” can be very significant in foundation investigations
because of misinterpretation that bedrock is at a higher elevation than
actual.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 51
48. In general, the quartz-poor mafic rocks develop a
weathering profile, also typical of many
metamorphic rocks, which is characterized by four
zones:
1. An upper zone of residual soils that are
predominantly clays with small amounts of
organic matter (equivalent to the A and B
horizons of pedological soils)
2. An intermediate zone of residual soil,
predominantly clayey, but with decomposition
less advanced than in the upper zone.
3. A saprolite zone in which relict rock structure is
evident and the materials are only partially
decomposed, which grades to a weathered rock
zone
4. The weathered rock zone where rock has only
begun alteration
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49. Clay soils are the product of decomposition. The clay type is related
strongly to the rainfall and drainage environment (Grim, 1962) as
follows:
Low rainfall or poor drainage; montmorillonite forms as
magnesium remains.
High rainfall and good drainage; kaolinite forms as magnesium is
removed.
Hot climates, primarily wet but with dry periods; humic acids are
lacking, silica is dissolved and carried away, and iron and aluminum
are concentrated near the surface (laterization).
Cold, wet climates; potent humic acids remove aluminum and iron
and concentrate silica near the surface (silcrete).
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53. ATTERBERG LIMITS
The Atterberg limits are a basic measure of the critical water
contents of a fine-grained soil: its shrinkage limit, plastic limit, and
liquid limit. As a dry, clayey soil takes on increasing amounts of water,
it undergoes distinct changes in behavior and consistency.
A fine-grained soil can exist in any of several states; which state depends
on the amount of water in the soil system. When water is added to a dry
soil, each particle is covered with a film of adsorbed water. If the addition
of water is continued, the thickness of the water film on a particle
increases. Increasing the thickness of the water films permits the particles
to slide past one another more easily. The behavior of the soil, therefore, is
related to the amount of water in the system. Approximately sixty years
ago, A. Atterberg defined the boundaries of four states in terms of "limits"
as follows R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 57
54. ATTERBERG LIMITS
Liquid limit: The boundary between the liquid and plastic states;
Plastic limit: The boundary between the plastic and semi-solid
states;
Shrinkage limit: The boundary between the semi-solid and solid
states.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 58
55. ATTERBERG LIMITS
These limits have since been more definitely defined by A. Casagrande
as the water contents which exist under the following conditions:
1. Liquid limit
The water content at which the soil has such a small shear strength that it
flows to close a groove of standard width when jarred in a specified
manner. The Liquid Limit, also known as the upper plastic limit, is the
water content at which soil changes from the liquid state to a plastic state.
OR
It is the minimum moisture content at which a soil flows upon application
of very small shear force.
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56. ATTERBERG LIMITS
2. Plastic limit
The water content at which the soil begins to crumble when rolled
into threads of specified size.
It is defined as “The moisture content at which the soil behaves
like a plastic material is called plastic limit”
“The moisture content at which the soil begins to crumble when
rolled up into a thread of 3 mm in diameter”
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 60
57. ATTERBERG LIMITS
3. Shrinkage limit: Shrinkage limit is defined as “the moisture content at which the soil
change from a semi solid state to a solid state”
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58. SOIL FORMATIONS: GEOLOGIC
CLASSES AND CHARACTERISTICS
Soils are classified geologically by their origin as residual, colluvial,
alluvial, eolian, glacial, or secondary soils.
The various geologic classes exhibit characteristic modes of occurrence.
Classifying soils by geologic origin, describing the formation in
terms of their mode of occurrence, and considering both as related to
climate, provide information on the characteristics of gradation,
structure, and stress history for a given deposit.
Knowledge of these characteristics provides the basis for formulating preliminary judgments
on the engineering properties of permeability, strength, and deformability; for intelligent
planning of exploration programs, especially in locations where the investigator has little or no
prior experience; and for extending the data obtained during exploration from a relatively few
points over the entire study area.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 62
60. CLASSES AND MODE OF OCCURRENCE
Residual Soils
Developed in situ from the decomposition of rock, residual soils have
geomorphic characteristics closely related to the parent rock.
Colluvial Soils
Colluvium refers to soils transported by gravitational forces. Their modes of
occurrence relate to forms of landsliding and other slope movements such as
falls, avalanches, and flows.
Alluvial Soils
Alluvium is transported by water. The mode of occurrence can take many
forms generally divided into four groups and further subdivided. Eg. marine
deposits. R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 64
61. CLASSES AND MODE OF OCCURRENCE
Fluvial or river deposits include stream bed, alluvial
fan, and floodplain deposits (point bar, clay plugs, natural levees,
back swamp), deposits laid down under rejuvenated stream
conditions (buried valleys, terraces), and those deposited in the
estuarine zone (deltas, estuary soils).
Lacustrine deposits include those laid down in lakes and
playas.
Coastal deposits include spits, barrier beaches, tidal
marshes, and beach ridges.
Marine deposits include offshore soils and coastal-plain
deposits. R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 65
62. CLASSES AND MODE OF OCCURRENCE
Eolian Soils: Eolian deposits are transported by wind and occur as dunes, sand sheets,
loess, and volcanic dust.
Glacial Soils: Soils deposited by glaciers or glacial waters can take many forms,
subdivided into two groups:
1. Moraines are deposited directly from the glacier as ground moraine (basal till, ablation till,
drumlins) or as end, terminal, and interlobate moraines.
2. Stratified drift is deposited by the meltwaters as fluvial formations (kames, kame terraces,
eskers, outwash, kettles) or lacustrine (freshwater or saltwater deposition).
Secondary Deposits: Original deposits modified in situ by climatic factors to produce
duricrusts, permafrost, and pedological soils are referred to as secondary deposits. The duricrusts
include laterite, ironstone (ferrocrete), caliche, and silcrete.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 66
63. FOUNDATION CONDITIONS
Generally favorable foundation conditions are associated with (1) medium
dense or denser soils characteristic of some stream channel deposits, coastal
deposits, and glacial moraines and stratified drift; (2) overconsolidated
inactive clays of some coastal plains; and (3) clay–granular mixtures
characteristic of residual soils formed from sialic rocks.
Marginal foundation conditions may be associated with glacial lacustrine
clays and soils with a potential for collapse such as playa deposits, loess, and
porous clays.
Poor foundation conditions may be associated with colluvium, which is
often unstable on slopes; granular soils deposited in a loose condition in
floodplains, deltas, estuaries, lakes, swamps, and marshes; active clays
resulting from the decomposition of mafic rocks and marine shales, or
deposited as marine clays and uplifted to a coastal plain, or deposited by
ancient volcanic activity; and all organic deposits.
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67. RESIDUAL SOILS
Residual soils develop in situ from the disintegration and
decomposition of rock.
The distinction between rock and soil is difficult to make when the
transition is gradual, as is the case with most rocks.
Chemical decomposition produces the most significant residual soil
deposits.
Mechanical weathering produces primarily granular particles of
limited thickness, except in marine shales.
The depth and type of soil cover that develop are often erratic, since
they are a function of the mineral constituents of the parent rock,
climate, the time span of weathering exposure, orientation of weakness
planes (permitting the entry of water), and topography.R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 71
68. RESIDUAL SOILS-ROCK TYPE RELATIONS
AND CLIMATE
Igneous and metamorphic rocks composed of silicates and oxides produce thick,
predominantly clay soils.
Sandstones and shales are composed chiefly of stable minerals (quartz and clay),
which undergo very little additional alteration. It is the impurities (unweathered
particles and cementing agents) that decompose to form the relatively thin soil
cover.
Carbonates and sulfates generally go into solution before they decompose. The
relatively thin soil cover that develops results from impurities.
Marine and clay shales generally undergo mechanical weathering from swelling
with some additional chemical decomposition.
Soil profile development is related primarily to rainfall, but temperature is an
important factor. Very little soil cover develops in either a cool-dry or hot-dry
climate. Cool-wet zones produce relatively thick soil cover, but tropical climates
with combinations of high temperatures and high rainfall produce the greatest
thicknesses.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 72
69. COLLUVIAL DEPOSITS
Colluvial soils are materials displaced from their original
location of formation, normally by gravitational forces during
slope failures.
They typically represent an unstable mass, often of relatively
weak material, and are frequently found burying very weak
alluvial soils.
Their recognition, therefore, is important.
Mode of Occurrence Colluvium is found on slopes, or at or far
beyond the toe of a slope. Displacements from the origin can vary
from a few inches to feet for creep movements, to tens of feet for
rotational slides, and many feet or even miles for avalanches and
flows. R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 73
71. ENGINEERING SIGNIFICANCE –
UNSTABLE MASSES
When colluvium rests on a slope, it normally represents an
unstable condition, and further slope movements are likely.
In slides, the mass is bounded by a failure surface along which
residual (or slightly higher) strengths prevail, representing a
weakness surface in the mass that is often evidenced by
slickensided surfaces.
The unconformable mass on the slope blocks the normal slope
seepage and evaporation because of its relative impermeability,
resulting in pore-pressure buildup during the rainy season, and a
further decrease in stability.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 75
72. ENGINEERING SIGNIFICANCE –
UNSTABLE MASSES
Slope movements of colluvium are common, and before total
failure range from the barely perceptible movements of creep to
the more discernible movements of several inches per week.
Movements are normally periodic, accelerating and decelerating,
and stopping completely for some period of time (the slip-stick
phenomenon).
The natural phenomena causing movements are rainfall, snow
and ice melt, earthquake-induced vibrations, and changing levels
of adjacent water bodies resulting from floods and tides.
Cuts made in colluvial soil slopes can be expected to become
much less stable with time and usually lead to failure, unless
retained. R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 76
73. ALLUVIAL DEPOSITS
Fluvial refers to river or stream activity. Alluvia are the
materials carried and deposited by streams. The stream
channel is the normal extent of the flow confined within
banks, and the floodplain is the area adjacent to the
channel which is covered by overflow during periods of
high runoff.
It is often defined by a second level of stream banks.
Intermittent streams flow periodically, and a wash, wadi,
or arroyo is a normally dry stream channel in an arid
climate.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 77
74. ALLUVIAL DEPOSITS
Fluvial refers to river or stream activity. Alluvia are the
materials carried and deposited by streams. The stream
channel is the normal extent of the flow confined within
banks, and the floodplain is the area adjacent to the
channel which is covered by overflow during periods of
high runoff.
It is often defined by a second level of stream banks.
Intermittent streams flow periodically, and a wash, wadi,
or arroyo is a normally dry stream channel in an arid
climate.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 78
75. ALLUVIAL DEPOSITS
Meandering
of the Colorado
River in
rejuvenated
plateau of
sedimentary
rocks.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 79
76. ALLUVIAL DEPOSITS
Geologist needs to have knowledge of
• Boulder zone (also headwater tract, young or early stage)
• Floodway zone (also valley tract, mature or middle stage)
• Pastoral zone (also plain tract, old age or late stage)
• Estuarine zone (at the river’s mouth)
Rejuvination, Buried channels.
Straight channels, croocked channels, braided channels, meandering streams, oxbow lakes.
Their sedimentary characteristics.
Discussing each in detail, is out of scope of this lecture.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 80
78. ENGINEERING CHARACTERISTICS OF
FLUVIAL SOILS
Fluvial deposits are typically stratified and extremely variable, with frequent interbedding.
Permeability in the horizontal direction is significantly greater than in the vertical direction.
Unless subjected to the removal of overburden by erosion or desiccation, the deposits are
normally consolidated. Clays are soft and sands are in the loose- to medium dense state.
Boulders, Cobbles, and Gravel
The coarser sizes occur in the beds of youthful streams, in buried channels, and in the upper
portions of alluvial fans in arid climates. Permeability in these zones is very high.
Sands and Silts
Sands and silts are the most common fluvial deposits, occurring in all mature- and late-stage
stream valleys as valley fills, terraces, channel deposits, lag deposits, point bars, and natural
levees. They are normally consolidated and compressible unless prestressed by overburden
subsequently removed by erosion, or by water table lowering during uplift.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 82
79. ENGINEERING CHARACTERISTICS OF
FLUVIAL SOILS
Silty sands deposited as valley fill in an arid environment are often lightly
cemented with salts and other agents, and prone to collapse upon saturation
following the initial drying.
Clays
Clay soils are not encountered in the boulder zone and are relatively
uncommon in the floodway zone, except for deposits along the river banks
and on the valley floor during flood stages. In these deposits the soils are
usually clayey silts.
In the backswamp areas, clays are generally interbedded with silts and
sands and are often organic, containing root fibers.
R. R. GADGIL, DEPT. OF EARTH SCIENCE, GOA UNIVERSITY 83
Engineering properties of rocks pg43
International Society for Rock Mechanics ISRM
Ayday and Grktan (1992) developed the following empirical correlation between L and N-type Schmidt hammer rebound numbers for the ISRM (1978b) test procedure
Rn(N) = 7.124 + 1.249Rn(L) (r2 = 0.882)
where Rn(L) and Rn(N) are, respectively, the L and N-type Schmidt hammer rebound numbers; and r2 is the determination coefficient.
Engineering properties of rocks pg43
International Society for Rock Mechanics ISRM
Engineering properties of rocks pg44
Engineering properties of rocks pg43
Slaking = Combine (quicklime) with water to produce calcium hydroxide
Engineering properties of rocks pg43
Characteristics of Geological Materials and foundations – A field guide pg39
Characteristics of Geological Materials and foundations – A field guide pg40
Characteristics of Geological Materials and foundations – A field guide pg41
Characteristics of Geological Materials and foundations – A field guide pg40
Characteristics of Geological Materials and foundations – A field guide pg40
Engineering Geology by Krynine and Judd pg78
Engineering Geology by Krynine and Judd pg78
Engineering Geology by Krynine and Judd pg78
Engineering Geology by Krynine and Judd pg78
Characteristics of Geological Materials and foundations – A field guide pg131
Characteristics of Geological Materials and foundations – A field guide pg131
Characteristics of Geological Materials and foundations – A field guide pg132
Characteristics of Geological Materials and foundations – A field guide pg132
Characteristics of Geological Materials and foundations – A field guide pg132
Characteristics of Geological Materials and foundations – A field guide pg135
Characteristics of Geological Materials and foundations – A field guide pg135
Characteristics of Geological Materials and foundations – A field guide pg138
Characteristics of Geological Materials and foundations – A field guide pg139
Characteristics of Geological Materials and foundations – A field guide pg140
Characteristics of Geological Materials and foundations – A field guide pg140
Engineering Properties of rocks pg116
Engineering Properties of rocks pg117
Engineering Properties of rocks pg118
Engineering Properties of rocks pg118
Characteristics of Geological Materials and foundations – A field guide pg142
Characteristics of Geological Materials and foundations – A field guide pg143
Characteristics of Geological Materials and foundations – A field guide pg140
Characteristics of Geological Materials and foundations – A field guide pg145
Characteristics of Geological Materials and foundations – A field guide pg146
Characteristics of Geological Materials and foundations – A field guide pg146
Characteristics of Geological Materials and foundations – A field guide pg146
Characteristics of Geological Materials and foundations – A field guide pg146
http://www.aboutcivil.org/atterberg-limits.html
http://www.aboutcivil.org/atterberg-limits.html
http://www.aboutcivil.org/atterberg-limits.html
http://www.aboutcivil.org/atterberg-limits.html
http://www.aboutcivil.org/atterberg-limits.html
Characteristics of Geological Materials and foundations – A field guide pg159
Characteristics of Geological Materials and foundations – A field guide pg270
Characteristics of Geological Materials and foundations – A field guide pg159
Characteristics of Geological Materials and foundations – A field guide pg160
Characteristics of Geological Materials and foundations – A field guide pg160
Characteristics of Geological Materials and foundations – A field guide pg161
Characteristics of Geological Materials and foundations – A field guide pg162
Characteristics of Geological Materials and foundations – A field guide pg162
Characteristics of Geological Materials and foundations – A field guide pg162
Characteristics of Geological Materials and foundations – A field guide pg161
Characteristics of Geological Materials and foundations – A field guide pg161
Characteristics of Geological Materials and foundations – A field guide pg178
Characteristics of Geological Materials and foundations – A field guide pg178
Characteristics of Geological Materials and foundations – A field guide pg179
Characteristics of Geological Materials and foundations – A field guide pg179
Characteristics of Geological Materials and foundations – A field guide pg182
Characteristics of Geological Materials and foundations – A field guide pg182
Characteristics of Geological Materials and foundations – A field guide pg182
Characteristics of Geological Materials and foundations – A field guide pg182
Characteristics of Geological Materials and foundations – A field guide pg183
Characteristics of Geological Materials and foundations – A field guide pg183
Characteristics of Geological Materials and foundations – A field guide pg183
Characteristics of Geological Materials and foundations – A field guide pg200
Characteristics of Geological Materials and foundations – A field guide pg200