Hello everyone and welcome back.
This is a new series of lessons; in this one
and the next few
lessons, we are going to learn the essential
aspects of subsurface investigation.
Now, today’s
lesson we are going to talk about some introductory
aspects of this subject and we are going to
learn a few things about how record keepings
are to be done.
.
Before we carry on with the presentation of
today’s subject topic, we are going to discuss
the
questions that were asked as part of the last
presentation.
The first question was what are the
main differences in sediment transport by
flowing water and wind?
So essential difference, the
basic processes involved in sediment transport
by both water and wind are quite similar.
But the basic difference arises because of
the fact that the ((…Refer Slide Time: 1:59))
of the
sediment particles that are been transported
by this agents, they vary quite a bit because
the unit
weight under ambient conditions of air is
about 1000 of that of water.
So, what happens because
of that is in case of wind, secondary suspension,
secondary transport, a transportation process
is
triggered because of some secondary effects.
For example, saltating clasts if they go and
hit another particle when the land at the
ground
surface, then those particles because of collision
may actually get transported because of there
being, they are taken into suspension and
transported.
So, this kind of this sediment transport
1
.processes, this type of secondary triggering
of sediment transport process is not generally
observed in case of water transport.
The second question that was asked was why
ice laid deposits is usually poorly sorted
while
fluvial and aeolian deposits are usually well
sorted?
Now, ice laid or ice can actually transport
huge sized clasts, say upto bolder sized clasts
and as a result, the spectrum of grain sizes
that are
present in an ice lane, ice laid sediment
actually covers a very wide range of grain
sizes;
whereas, that kind of capability is not there
when you are considering agents like water
and
wind.
As a result, the grain size distribution is
actually, it varies over a very narrow band.
So, because
of because of this fundamental reason, the
ice laid deposits are going to be a little
bit more rich in
representing grain sizes as compared to sediments
laid by water transport and wind.
Then the third question that was asked was
name two poorly sorted deposits laid in marine
and
fluvial environments.
In marine environments the sediments that
are laid they are generally
relatively very fine grain because very low
velocity environment because of the very low
velocity environments that generally prevails
near the bottom of the oceans.
In some cases though, the velocity can actually
go up quite substantially and that may trigger
processes which you are aware or the counter
parts of which are known to you, known to
many
of you.
If it takes place on the ground such as land
slide, the sub aerial land slide, those kind
of
processes also take place under water and
they actually provide a very high velocity
or high
energy transportation environment and in those
environments, if a large grain size distribution
is
available within the sediment that is undergoing
submarine land slide, then the deposits that
are
going to form when the land slide debris flow
to a different location also have got representation
from a very large spectrum of grain sizes.
So, in some situations turbidites could have
a little bit more wide grain size distributions
than the
mud deposits, so called mud deposits that
are found at the bottom of an ocean known
as a mud.
Now the fluvial, as far as the fluvial environment
is concerned, one type of deposit that comes
to
mind is the deposits laid in alluvial fans.
So, in that situation, a high energy mountain
stream
actually enters a very flat line area and
suddenly the velocity of the water flow decreases
quite
substantially.
As a result, all the sediments that are being
carried, all the grain sized that are being
carried by
the mountain stream, they get deposited within
the alluvial fan.
As a result, alluvial fans have got
a very heterogeneous structure which often
includes lenses of very fine grain material
within
coarser matrices or vice versa.
The forth question actually involves explanation
of the few terms; the first one was point
bar.
So,
in this case, the deposits, actually it is
basically a fluvial deposit and let us consider
a meandering
stream and the meandering stream is going
like this and say, this is the flow direction.
2
..
So, what happens actually is on the insides
of the curve, the velocities are usually smaller
in
comparison with the velocity near the outside,
near the outside.
So, this is the inside of a curve
and this particular, for this particular band,
this is the outside of the curve.
So here, we have got
higher velocity, higher velocity and that
often triggers actually erosion and what you
have got in
the inside is relatively smaller velocity
and this triggers deposition and since this
particular
deposit is, deposition is taking place right
near the margin of the or the perimeter of
this
particular stream, so the velocity is relatively
much higher compare to a velocity which is
laterally further away from the stream bank.
So, what you get here is the deposits that
form in this process, they contain, they are
rich in
coarser grains 
and this type of deposit is called point bar,
point bar deposits.
So, that actually
explains the term point bar.
Rewarding back, the second question was what
is meant by kame
moraine, kame glacial deposit.
And, this is a sort of long ridge like deposit
that forms because of
melt water, glacial melt water, streams of
which actually flow underneath the ice surface,
underneath the surface of the ice and they
deposit, they deposit coarser grain coarser
grained
sediments such as actually varying within
gravel size particles.
These ridges are called kame
deposits.
Now, the third part of the third fourth question
involves explanation of the word yardang.
This is
also a long drawn out ridge but in this case,
the erosional process that is responsible
for
development of this type of land from is basically
wind erosion and because of that softer,
unidirectional or if the wind direction is
relatively uniform in a single direction,
then they
actually heat up relatively softer areas of
the bed rock surface and what is left with,
what you are
left with is a long ridge of, long ridge jugging
out from a relatively flatter surface.
So, this type
of deposit, this type of this type of land
form actually is called yardang.
So, that takes care of the
questions.
3
..
So, what we do now is to move to the subject
matter or today’s presentation.
First of all, the
objective - what we want to learn from this
particular presentation; we are going to learn
the
processes, essential processes of subsurface
investigation, investigation of the stratigraphy,
stratigraphy condition underground and ground
water condition.
We are going to list the, we are going to
list the plans or considerations that are
involved in
developing a subsurface investigation program
and we also are going to learn how to maintain
an
appropriate field record of the investigation
activities in order to help the designer to
make, to
pass on the information to the designer or
to the engineer about what was the likely
condition of
subsurface deposits in terms of joints or
open form structures or ground water and so
on and so
forth because these are very important clues
that the engineer will require in designing
a
particular facility at that site.
So, these are the three main objectives of
this particular lesson.
4
..
Now, we consider the objectives actually of
the subsurface investigation activities themselves
and so why we after all undertake subsurface
investigation?
So, what we want to find after we
develop or conduct a subsurface investigation
program?
So first of all, what we need to find or
what we are interested to find is to identify
and delineate geologic units.
For example; a particular site may be underlained
by a layer of soil.
So, this one here is a layer of
say sand and then underneath that layer, there
could be a layer of silty clay.
We do not know
actually in engineering terms, what are the
meanings or what are the, what are the actual
meanings of these terms but we are going to
learn those things later on when we talk about
the
textural classification of soils as we did
in case of rock earlier.
5
..
Now, underneath the silty clay, there could
be a sand stone bed rock which could be interlayered
with, interlayered, say siltstone 
and underneath the sand stone layer, there
could be a silt stone
layer.
So, in a subsurface, from subsurface investigation,
what we want to find is we want to
actually find the sequence of these subsurface
units that are going to be underlained, that
are
going to be below underneath a particular
site.
We also want to find how the layer, these
individual layers thicken or thins out in
a particular
direction.
So, we not only want to find these thicknesses,
these thicknesses of individual units;
we also want to find the slope of these units.
If you recall, this slope is called the depth
of these
interbeds or this interfaces.
So, this is what we want to actually find
in a sense from a subsurface
investigation, one of the things that we want
to find from a sub-surface investigation.
6
..
Then the second thing is we want to describe
each of those units systematically and this
description should include information on
field identification of these units.
For instance, the
inspector needs to say whether the layer that
is being encountered during the subsurface
investigation is that consisting of sand size
particles or it is mainly composed of clay
size
particles or whether it is sand stone or lime
stone or whatever.
So, this is required to be identified
in the field itself and we will see how these
things are recorded and later on in this particular
presentation.
And the second thing also, second thing also
is important is the extent of weathering or
density
or compressibility of these units.
We need to identify the features such as joints,
faults and
slickenside’s; some of this terms are known
to you, some of this terms are not, we are
going to
explain these terms later on, the unknown
terms later on.
This is important because these joints,
faults and slickenside’s ,they actually
present plains of weaknesses which might be
acting in
future after the construction of a facility
on top of the this particular formation as
plains of
weaknesses through which failure, ground failure
might be triggered because of the change in
this stress region caused by the construction.
Then the fourth particular thing that we are
interested to find from subsurface investigation
is we
conduct simple index tests during the investigating
itself to get a picture about how strong is
the
subsurface unit against a certain type of
load.
7
..
We continue with the list of objectives.
Subsurface investigation also quite often
involves
assessment of hydrologic condition.
What we want to find in this case; how the
ground water
underneath a particular area is or what is
the condition of ground water that is there
within the
subsurface deposit underneath site.
Then we want to extract also samples of geologic
units such as different types of soils or
different types of rocks for subsequent laboratory
testing, we also sometimes sample ground
water samples, take extra ground water samples
for laboratory chemical tests and finally
another
important objective of subsurface investigation
is to install instrumentation which is going
to be
left underground for monitoring of the time
dependent changes of subsurface condition
such as
say for example, if the ground water flow,
it has got a seasonal variation, then how
the ground
water regions varies over time, we want to
know that; whether it rises to the surface
or what
depth it actually falls to.
This has implication in the design of a particular
facility at that site.
So,
these are the main objectives of a subsurface
investigation program.
8
..
Now first question that comes to mind is how
much of an area is to be covered in a subsurface
investigation program?
Now, the spatial coverage, the spatial coverage
actually depends on the
purpose of investigation and subsurface variability.
Now, if an investigation is being undertaken
for a very very important project, then the
spatial coverage may actually have to extend
a little
bit further out of the foot print of that
particular project or the construction, proposed
construction so that the effect of the proposed
construction on the surrounding areas is also
properly accessed during the design process.
Then the second thing is how much of variability
is there in the subsurface condition?
If the
ground condition is highly variable that means
the layers are, layers are highly irregular
and they
do not show any particular continuity over
a large lateral extent; in that situation,
the
investigation locations need to be relatively
closed spaced in comparison with a situation
where
the ground condition is homogeneous, relatively
homogeneous and uniform.
Then the second aspect that actually governs
the spatial coverage of a subsurface investigation
program is how much of an area, how much of
an area is being proposed for the construction
of a
facility?
So, the spatial coverage should at least cover
the project area and then as I indicated just
a few minutes back, the extant of coverage
of the subsurface investigation should be
an or should
also cover an area outside of the perimeter
if required because this allows the designer
to assess
the influence of a particular construction
on the surrounding facilities, surrounding
facilities
which is not within the project area.
So, let us try to understand what is meant.
9
..
We have dealt with these things some time
back, this aspects sometime back.
Let us say, let us
say there is a hill side and this hill side
what is proposed, what is proposed is construction
of a
hill road on the side of the hill and what
we are looking here is a vertical section
really, vertical
section of a hill slope.
So, this is the proposed highway, so this
one is the proposed highway.
Now, you could actually argue that since the
highway is proceeding in a plane perpendicular
to
the tablet here, what we are going to do is
we are going to drill a series of investigation
hole
along the center of the right of way and that
is going to be or that is going to be yet.
Now,
whether that is sufficient or not, that is
what we want to actually find out here.
Now, let us say, this particular hill slope
is underlained by a jointed rock and the joint
set, one of
the joint sets is oriented in this manner.
Now, if you have got this kind of joint set,
so this is the
joint set; if you have got this type of joint
set, then if your proposed investigation of
drilling to
bed rock is only along the highway center
line, then you are not going to be or you
would not
able to see what is the depth of the joint
as you move laterally from the center line
of the
proposed highway.
So, in order to capture the geometry of the
joint sets, we have to have subsidiary investigation,
down slope and up slope of the center line
of the proposed highway.
So, we need to have a set of
boreholes laid out in this manner and then
we can easily find out the elevations from
the drilling
information from these boreholes of a particular
bedding or a particular joint and then we
have
got a better idea, better picture of the depth
of the joint set in a direction perpendicular
to the
proposed highway.
Now, that is important that is very important
is because if you are proposing a highway
through a
hill side which is underlained by a jointed
rock with a joint set like this, then if you
excavate in
this manner as shown that is going to be triggering
a possibility of rock slides as we have learned
10
.from a presentation sometime back.
So, this type of orientation, joint orientation
is not really
very good for the highway facility proposed
here.
.
So instead of that, what we also learned earlier
is that a preferable orientation of joint
set would
be like this.
So, if the joints were to be orientated like
this, then if we have got a steep cut at this
location, then the cut is going to be relatively
more stable.
So, these considerations are verified
from having a well laid out investigation,
subsurface investigation land.
.
11
.So, you saw there that we not only need to
investigate along the proposed alignment of
the
highway, we also investigated laterally a
little bit further out from the center line
of the highway.
So, that is what is meant in the last in the
last particular point here; so you should
take a note of
this particular aspect as well.
.
Now, the second question that comes to mind
is what should be the spacing and depth of
the
locations of the investigation program, to
what depth actually we should carry out the
subsurface
investigation and what should be the spacing
in between two consecutive locations of
investigation?
Now, it is quite obvious if the investigation
is for deciding the preliminary alignment
of
particular linear facilities such as highway
or railway; then the investigation can be
carried out at
a relatively wider spacing in comparison with
the corresponding investigation that is being
undertaken for a detailed designed project
of the same facility.
So, a guide line in this respect is given
on this table here; if we have got a preliminary
investigation and if we have got uniform subsurface
conditions, if the subsurface condition is
relatively uniform, then a spacing of 100
to 150 millimeter between two consecutive
investigation locations is often considered
sufficient.
Now, if we have got a very important structure
and I mean, if the project is at a detailed
design
stage and condition of the subsurface layers
is uniform once again; in that case, the spacing
is
going to be much less and the common practice
is to go for boreholes, every one borehole
every
30 meters or there should be one exploration,
one exploration location covering approximately
1000 square meter area.
Then the third guidance that we have got in
this respect is that if the subsurface condition
is
highly variable that means the layers, the
subsurface layers they are steeply deeping
and they are
12
.also pinching out or thickening in all different
directions; in that kind of situation, subsurface
spacing should be even less and 10 to 15 meters
spacing between two consecutive boreholes
is
often consider sufficient in this respect.
Then we also have to find upto what depth
we have to investigate and a simple guidance
in this
respect, it concerns the change in vertical
stress, so the guidance goes like this; if
the change in
vertical stress is 10% or less of the initial
vertical stress, then that should be the level
up to which
we want to conduct an investigation.
So, let us try to understand this particular
point little bit
more.
.
Let us say, we have got a ground surface like
this.
So, this one is the ground surface and again
we are looking at a vertical section and let
us say, we want to actually construct an embankment
dam at this location, embankment dam at this
location.
Now, because of this dam construction,
the soil elements underneath the dam, it will
feel a larger vertical pressure in comparison
with its
original value.
So, let us say, originally you had a vertical
pressure at that level of sigma v prime
that arose because of a soil column of that
much of depth.
So, this was the original vertical pressure.
So, if you consider the unit weight of the
soil column
to be gamma and the depth from the surface,
ground surface before the embankment dam was
constructed that was gamma d, then after the
dam is constructed roughly, you will also
have to
include the weight because of the material
used in dam construction as well.
So, this has got a
unit rate of gamma 1 and this depth is d1.
So, what we have got here is, finally is a
pressure of
gamma 1 d1.
So initially, so what you had here, so let
us call it sigma vf where sigma vf is the
over burden
pressure after construction 
and sigma vi is the initial over burden pressure.
So, in this case, sigma
vi is equal to as we have said in the sketch
there, it is equal to actually, is equal to
gamma times d
whereas sigma vf is equal to gamma times d
plus gamma 1 d1.
13
.Now, what happens actually; as you go down
deeper, the effect of the construction, effect
of the
weight of the embankment actually decays with
depth.
So, what we have got actually, if you
consider the final over burden pressure, then
as you go down deeper - let us erase a little
bit more
in order to get clarity - so what you have
got sigma vf decreases or delta sigma vf;
if we plot
sigma vi minus sigma vf, so this one here
is sorry sigma vf minus sigma vi.
.
So, this value is actually sigma vf minus
sigma vi at a given depth, at a given depth.
So, this
actually decreases gradually with depth typically.
Now typically, the over burden pressure sigma
vi, so both these things are being plotted
against depth; sigma vi actually is going
to gradually
increase with depth and let us say, we are
plotting sigma vi divided by 10.
So, 10% of sigma vi,
we are plotting and you can see that this
is the depth upto which sigma vf minus sigma
vi is
greater than or equal to 0.1 times sigma vi.
So basically, this much of depth requires
investigation, requires subsurface investigation;
so upto that depth, you have to conduct the
subsurface investigation.
14
..
Now, we look at the different types of methods,
different methods that we normally use, that
are
normally used in subsurface investigation.
So, one class of methods that involves actually
inserting a probe or getting or intruding
into the subsurface layers.
So, this type of investigation
is called the intrusive methods.
So, intrusive method includes all those methods
of drilling sampling and in situ testing,
this also
includes excavation of a test pit; we are
also going to look at the procedures later
on and it also
includes trenching.
And secondly, there could be non-intrusive
methods, these methods do not involve insertion
of a
particular probe in the ground and will see
the salient features of these methods later
on in one of
the future presentations and they include
seismic velocity profiling, ground penetrating
radar and
electromagnetic and resistivity surveys.
So here, we do not actually intrude in the
subsurface
deposits; whereas in intrusive methods, some
of which are going to be discussed today,
we are
going to actually insert something - a probe
or a drill stem or something into the subsurface
deposit.
15
..
Now, before we get into the processes, we
want to actually see the details, actually
we are going
to or let me get the points straight; we are
going to talk about intrusive methods in the
next
presentation and non-intrusive methods, we
are going to look at the details of these
methods in
one of the later presentations after the next.
Now, we want to actually look at the record
keepings before we get into the procedural
details of
the intrusive method and non-intrusive methods
because it is extremely important actually,
I
should underscore this thing, it should not
be treated lightly.
It is extremely important to have a
very complete record about whatever is going
on during the subsurface investigation because
the
investigators report is the only thing that
actually gives the details of the different
types of
happenings during the subsurface investigation
to the designer of a particular facility and
if the
records are incomplete, then the inference
that the designer is going to draw from the
field record
is going to be insufficient and often misleading.
So, what are the different aspects that must
be included in a subsurface investigation
field report?
First of all, you need to very clearly mention,
the inspector should very clearly mention
what is
the exact location and time of investigation.
And, for this particular purpose, it is often
essential,
particularly when an investigation is undertaken
for a detailed project design stage, it is
very
essential to have the locations of investigation
properly surveyed in terms of their top elevation
or the elevation of the ground surface at
the location of the investigation as well
as the exact
location of the investigation reference to
some bench marks or the surveying monuments
or in
terms of GPS coordinates.
The second thing that must be included on
the field log is the name of the person who
is logging
as well as the name of the driller because
if the designer needs some information regarding
activities, regarding activities which are
not appropriately mentioned on the field log
which are
missed out from the field log; in that case,
the personnel who signs of the field log,
they can be
contacted.
16
.Then third thing is description of the equipment
and procedure used in a particular investigation.
That actually tells a lot about how much of
reliability can be placed on the information
presented
in the field log; that depends very strongly
on the procedure used in the investigation.
Then the
forth aspect that must be included in the
field log itself is the log of material characteristics
or
what kind of layers are being encountered
during the investigation process.
Then there should be a log of ongoing activity
and that should include whether any significant
or
all significant occurrences such as for example
let us consider a drilling activity that is
being
undertaken at a site underlained by jointed
bed rock and there could be actually a cavity
inside a
bed rock because of removal of rock material
by water or some other because of some other
reasons and if a drill stem is allowed to
be lowered within that cavity, then what is
going to
happen is if there is an effort to drill through
this particular cavity, then the drill rods
and the drill
bit is going to drop through the cavity and
the inspector must record that the drill string
drop
through a certain depth when the borehole
proceeded to a particular elevation because
that will
tell the designer that there are cavities
within bed rock which must have to be considered
while
designing a particular facility on top of
that surface.
Now, if that information is missing, then
the designer will assume that the bed rock
has got no
opening and the strength that he is going
to infer is going to be relatively more and
stability issue
will not be considered in the design because
of the presence of those cavities.
So, these types of
these regarding the ongoing activity must
be included in the field log itself.
Then there should be ground water observation,
ground water observation; whether the water
flow or water used in the progress of the
drill hole, that actually is vast within a
cavity, that also
should be mentioned here, water loss.
Then installation details of any instrumentation
like standpipe piezometer, we are going to
look
at the details of these particular or we are
going to look at the details of these things
later on.
So,
instrumentation details should also be mentioned
on the field log and as I mentioned earlier,
an
incomplete record is really a misleading set
of information.
17
..
Now, soil description; you have to describe
the subsurface units that are encounter during
the
investigation process.
Now, soil description should include all those
things; density or
consistency, structure, field moisture condition,
color or odor, particle shape such as angularity
and soil constituents - whether it is composed
of sand or whether it is composed of clay
or
whatever.
.
Now, the first aspect that needs to be included
in the description of the subsurface units
is density
and density is applicable, this is for coarse
grain soils actually; if you recall coarse
grain soils,
they derive there material strength basically
from interlocking between individual grains.
As a
18
.result, density becomes a very important
parameter affecting the strength of that particular
subsurface unit.
So here, we could have a spectrum of different
densities; it could go from very
loose to very dense.
So very loose is a type of or you can infer
actually, these different densities
by conducting very simple tests such as trying
to penetrate the formation by a steep by a
shovel
by the handle of a shovel or trying to insert
a rod into the deposit.
For instance, if you have got a very loose
deposit, then that particular deposit is easily
penetrated
with a handle of a typical shovel; whereas
if it is loose, then it can be penetrated
with a 13
millimeter diameter approximately, 13 millimeter
diameter steel rod.
Now, if you need to use a 2
kg hammer to drive that 13 millimeter diameter
steel rod, then you can say that the deposit
is
medium dense and if it is dense, then even
after hammering the rod, you would not be
able to
penetrate a depth of more than say 300 millimeter
or if the deposit is very dense, then the
penetration is less than about 25 millimeter
of the 13 millimeter diameter steel rod.
.
Second thing is consistency.
So, consistency actually is applicable for
fine grained soils such as
cohesive soils or clays.
These type of soils, they actually derive
their strength form inter granular
electrical bonds; we will see this aspects
later on.
The consistency of a fine grain soil can vary
from very soft to hard and here also I mention
a series of simple test that can be performed
on a
sample extracted while the investigation process
is going on and this test will tell the inspector
whether a soil is approximately very soft
or it is hard.
19
..
Then you have to mention structure; you have
to talk about structure of the particular
deposit.
Now, structure could be massive - massive
structure is relatively homogeneous and featureless,
no joints or bedding plains apparent within
the unit of soil or rock; it could be homogenous
homogenous is relatively uniform in composition
and color; it could be heterogeneous which
means non uniform in composition and color
and it could be layered - there could be parallel
layering or the layers could be pinching or
thickening in a particular direction or there
could be
laminations - these indicate very closely
spaced alternating layers of different soils.
Now, if you have got only two different types
of soils in terms of grain sizes; then laminated
soils are called varved soils.
20
..
More structural aspects; structures could
be seams - seams are basically layers which
are less
than 10 millimeter thick and they extent to
great depth, great lateral extents; there
could be lenses
- lenses are basically similar but they are
all limited lateral extent, similar to seam
but they are all
later limited lateral extent; then there could
be fissures or cracks of discontinuities within
the
within in the mass of soil; there could be
slickenside’s - slickenside’s are essentially
joints again,
fissure again but this fissures, the surface
of this fissures are very highly polished,
they are very
slippery; the soil can be cemented which means
there are inter granular cementing agents
between individual particles.
.
21
.Then you have to describe moisture color
and odor of a particular soil deposit.
Moisture
condition could be dry to wet.
Dry means there is no visible moisture, moist
means the deposit is
moist to touch but there is no free water
and wet means there is free water, free water
film
present on the surfaces of the individual
particles.
Then you have to also describe the color of
a particular soil unit and color have to be
described
as the sample is dug out of a particular borehole
because color changes with exposure to,
exposure to the ambient condition and color
actually include a primary color or there
could be a
secondary, you also have to include the description
of the secondary coloration such as patches
of a secondary color, this type of patches
are often called mottling and this particular
feature is
associated with ground water, with seasonal
or with time dependent ground water fluctuation
within layers.
So for example, the layers within which the
ground water level fluctuates, they have often
colors
which is basically, it has got a one, it has
got one primary color say orange and it has
got dark
patches and this particular type of coloration
is called mottled orange black.
Then you have to describe the odor and that
is important because for example if there
is a lot of
organic content within a particular soil,
then the odor is going to be indicative of
such organic
content.
.
Then finally, you have to name the soil constituent;
here you have to name the primary
constituent of the soil and this includes
say for example sand or clayey silt.
And, you also have to
name the secondary or tertiary soil constituent,
secondary or tertiary soil constituent; so
here you
use qualifiers such as trace, little, some,
with or and.
And, the percentages of the secondary or tertiary
constituent meant by these qualifiers are
indicated over there.
For example; if you have got little, if you
have got clayey silt with sand,
22
.that means it has got or it is primarily
a clayey silt soil but it has got 20 to 30%
of sand and it
could also include trace gravel as is given
in the example at the bottom of this particular
slide.
.
Now, we are going to continue with this particular
presentation, we are going to continue with
the description of rock units when we meet
in the next presentation and we are going
to look at
the details of how the information gathered
during the subsurface investigation, the systematic
information gathered during a subsurface investigation,
they are recorded and after that in the
next presentation itself, we are going to
move on to the inclusive testing methods.
With that actually, I am going to wrap this
particular presentation here and we are going
to
consider the question set of this presentation
together with the question that is going to
come
once we complete the lesson in the following
presentation.
So, until we meet for the next time,
bye for now.
Thank you very much.
23
.
