Hello everyone and welcome back.
Today we are going to look at list of geologic
considerations that are looked at in construction
of dam, bridge and roads, but before get
on with the today’s topic, we are going
to look at the question set of previous lesson.
.
And here are the questions.
The first question that I asked was a circular
horizontal
tunnel is to cross a thinly laminated rock
mass.
The laminations strike parallel to tunnel
axis and dip at 40 degree to horizontal.
Because of local topography the major principles
stress is parallel to the laminations.
You are asked to comment on tunnel stability.
..
Now this problem is quite similar actually
to the north polar tunnel headrace tunnel
that
we discussed when we were talking about geologic
considerations of tunnel in the
previous lesson, but in that one the tunnel
had a horseshoe alignment.
And here for
simplicity I asked you to consider the tunnel
to be circular.
So, this is the tunnel crosssection, and let
us say the laminations are 
like this.
In fact, the beddings are going to be
much more closely spaced than what I am drawing
here.
If you recall from the discussion that we
had while talking about classification of
structural features within rock masses on
laminations; anyway, so this is a rough sketch.
So, what is the direction of major principle
stress in this case is like this.
So, this is our
direction of sigma one.
So, in this case what is going to happen?
The laminations to the
top and left of this particular tunnel particularly
in this area are likely to squeeze into the
tunnel because of the release of stress during
tunnel excavation.
And so, what is going to
happen perhaps after a while, you are going
to end up with a tunnel bore 
of this type.
So, you can notice easily here that the tunnel
dimensions are smaller than it was
originally planned is going to be smaller
than it was originally planned near the top
and
left of this particular configuration.
So, that is the answer of the first question.
The
second question was how do you identify a
falling and a sliding rock wedge?
..
So, this one here, and let us consider first
a falling wedge.
Let us say the tunnel cross
section is like this for simplicity square
cross-section, and let us say we have got
a wedge
which is of this type.
This is going to be a falling wedge.
Now in this case if we neglect
the dilatancy on the top surface.
And actually what we are considering joint
set J 1 and J
2 in this particular case both strike parallel
to the tunnel axis.
So, this one is the tunnel
cross-section of the tunnel.
So, joint J 1 and J 2 both strike in the direction
parallel to the
tunnel axis in this case.
So, if we neglect in this case the resistance
due to dilatancy on surface one and purely
consider the frictional resistance mobilized
on plane two at the bottom of the wedge.
In
that case if the friction angle mobilized
on plane two.
So, if phi on plane two is greater
than or equal to the friction angle of the
joint surface; in that case we are going to
have
no problem, Whereas if we had this one less
than phi of the joint surface.
Then we would
have had 
falling wedge.
So, this is a very simple way of identifying
a falling wedge.
And similarly, on the sidewall, the considerations
are going to be quite similar; in this
case let us say we have got two joints again
making planes three and four.
Here if we
have phi on plane three or rather plane four
is greater than or equal to phi of the joint
surface.
This could be different from the phi on joint
J 2.
Then we are going to have no
problem 
and if we reverse the sign of the inequality.
So, if we go reverse on the
inequality, then we are going to have sliding
wedge.
.This actually the configuration that I used
in this particular illustration is very simply,
because what I assumed here is that the joint
sets strike parallel to the direction of the
tunnel axis.
Now if the joint set was to be skew with respect
to the axis of the tunnel,
then the calculations or the sketches become
much more complicated could become
much more complicated in fact.
But the principles of identifying the possibility
of rock
fall remain the same as the illustration that
we considered here, okay.
So, these are then
the answers to the questions that I gave you
in the previous lesson.
.
Now we move on with today’s lesson.
So, what we want to accomplish at the end
of this
particular lesson are the following.
We should be able to list the major geological
considerations in the construction of dams,
bridges and road cuts.
And we should be able
to identify countermeasures against rock mass
instability due to for instance
overstressing as result of the construction
of dam, bridges or road cuts and rock fall.
So,
those are the objectives.
And then let us begin the discussion; we are
going to move in
sequence.
First of all we are going to consider the
geological aspects used in dam design.
Then we are going to move on with the geologic
considerations in bridge foundation
design.
And finally, we are going to look at the aspects
concerning road cuts.
Now first
of all then the question comes what are the
different types of dams, what is dams?
Dams
are basically some barriers that are used
to retain either water or to retain some other
waste material such as mine wastes.
In the first case the dams are called water
retaining
.dams.
And in the second case the dams are called
tailings dams.
So, all the illustrations
here we are going to use the examples of water
retaining dams, but in principle the
discussion is going to hold for tailings dams
as well.
Now let us first look at what are
different types of dams used in civil engineering.
.
Now a dam could be a structure which actually
counteracts the lateral forces because of
the material retained in the illustration;
here I have shown water retained by the dam
cross-section of which is shown on this particular
sketch water as you can see is on your
left.
And the dam is a triangular is of a triangular
cross-section to the top right of this
particular sketch.
Now this dam actually is going to counteract
the lateral forces exhorted
on the dam body by the water by virtue of
its self weight.
So, this type of dam is called a gravity dam,
and a gravity dam could be constructed
using masonry or concrete or even using other
kind of open work or open type of
structures with some water type cladding on
the face.
Now let us consider another type
of dam.
..
This dam is called an arch dam.
The sketch that is shown here is actually
an oblique view
of a dam looking from little above from the
downstream side of the dam looking
upstream.
So, here what you have?
We have got water to the right.
And this one here is
our dam axis; it has got a curved shape in
plan as you can see.
This one is the right
abatement.
So, this is essentially the right bank of
the reservoir.
And this one here at the
bottom is another abatement; in this case
this is left abatement.
So, this one you can see a small block of
rock on the left of the sketch here.
And this one
here is again the right abatement of this
particular dam structure.
Now you can also see
near the middle a structure, and this structure
is called spillway, because it allows release
of water when the water tries to exceed the
highest water level for which this particular
structure is designed, okay.
So, that is in a sense a sketch of an arch
dam.
This type of
dam is called an arch dam, because here the
load because of water the lateral pressure
that is exhorted on the dam body by the water
is counteracted by arching action, where
the arch meets the right and the left abatement
as well as through the action of the
gravity.
And most of the load is taken, in fact, here
by the arching action shown by purple arrows
on this particular sketch that I just now
have drawn, okay.
So, that is another type of
dam.
Then let us go to another class of dam.
..
This type of dam is called arch embankment
or a rock field dam.
So, basically it is an
embankment; it is a multi zone embankment
here.
And in this case we have got water
retained on the left, and this is our dam
body.
This is the cross-section of the dam in fact;
this is the dam body cross-section.
And here we can see that the embankment is
a multi
zone embankment.
The outer part is called the shell, and typically
shell is constructed of
semi pervious heavy material.
And the inner part here is called a core,
and core is
typically constructed using well selected
fine grained soils such as clays; that is
in order
to prevent water from seeping through the
body of the dam.
And what you also see on the downstream face
of the core we have got another feature
and this particular thing here is made of
drain rock which is free flowing.
So, the purpose
of this is that if there is any water flowing
across the core that is going to be intercepted
and carried away through the drain and the
upright part of this drain is called chimney
drain, whereas the horizontal part of the
drain is called a drainage blanket.
And of
course, at the bottom we have got a foundation
which may be composed of soils
relatively impervious soils and rod rock.
Now also you should notice here is that the
core is taken down deeper into the
foundation material by a trench.
So, this particular part and the bottom of
the core is
called core trench.
Now this is done in order to prevent or in
order to minimize the water
seeping through the foundation material.
So, this type of dam is called an embankment
.dam.
I should also state here is that there are
several variants of this particular concept.
You can construct shell using again a multi
zone approach with the facing constructed
using a concrete face.
And inside of it you can construct the shell
using rock field.
So, those types of dams are
called concrete face rock field dams, and
they are also very popular in India as well
as
internationally.
So, these are different types of dams.
.
And then what we have to look at is what are
the considerations while selecting a dam
site.
So, which areas in fact are going to provide
a proper foundation for a dam?
So, first
we consider dam foundation on rock, and then
we are going to move on to dam
foundation on soils.
So, the desirable characteristics of a rock
foundation for a earth dam
or gravity dam or an arch dam; anyone of them
are as follows.
The rock should be
massive, impermeable, un-fractured, un-stratified
without folding or faulting, examples
being basalt, quartzite, compact limestone
and dolomite/
So, these are preferred foundation options
that a dam designer would like to have, but
that is not always possible.
And we might have to end up in selecting a
site underlying
by fractured heterogeneous or soluble rocks
or rocks susceptible to creep and
consolidation and slaking.
I am going to define what is meant by the
term slaking in the
next little bit.
These type of rocks actually present poor
foundation conditions; examples
.of such type of rocks include carstic limestones,
conglomerates, poorly compacted
limestone, shale and phyllite.
Now before I move on with the desired characteristics
of foundation on soil, let me
explain what is meant by slaking.
Now slaking is a term used to quantify the
characteristic of a rock which makes it susceptible
to chemical weathering.
So, what is
done in order to determine slaking is to take
a certain amount of rock specimen in a drum
constructed using a screen.
And that drum is partly submerged in water
and the rock
specimen within the wire mesh drum is rotated
using a pre specified manner, so that it
comes in contact with water several times.
And what is done afterwards is the amount
of rock material that is retained within the
wire mesh drum is measured.
And it is expressed as a percentage of the
weight of the
rock specimen that was originally taken within
the wire mesh drum.
Now the more the
weight retained within the drum after the
exposure to water, the less will be the
susceptibility of the rock to chemical weathering.
And In fact, soils or rather rock samples
such as volcanic rocks or sandstones, they
exhibit quite high slake durability.
In other words if you test those type of rocks
for in a
slaking test, then a large proportional of
the original weight is going to be retained
after
the repeated exposure to water, whereas rocks
such as shales are expected to exhibit a
remarkably small slake durability.
So, that is in a sense what is meant by slaking.
.
.And now with that explained, let us move
on to the characteristics or the considerations
that one needs to look at while selecting
a dam site or at a site underlying by soils.
So,
the soils underlying the dam need to be impermeable
or impermeable soils need to be
present within a reasonable depth underneath
the base of the dam.
And the soil should be
strong enough to support the weight of the
dam and reservoir without causing large
permanent deformation.
So, these are the aspects to consider when
selecting a soil site for constructing a dam.
So,
this requires some measures like for example,
if there is a soil site earmark for dam
construction at which the top few meters are
underlying by compressible organic soils.
Then those organic soils need to be excavated
and replaced before the dam construction
can be taken up at that particular site.
.
Now with these stated we can now consider,
what are the important aspects we need to
look at while selecting a dam site?
Now the main three aspects that we are going
to look
at are loading, failure modes of dams and
load transfer mechanisms.
We are going to
look at these topics one by one.
So, first we consider loads that are imposed
by a dam and the reservoir that is going to
be
supported by the dam or the tailings mass
that is going to be retained by the dam.
Loads
are of two types; loads could be permanent.
They include the weight of the dam and
water and permanent pore water pressurize
and load on the other hand could be
.incidental.
Such loads include earthquakes, temporary
pore water pressure increase or
wave loading because of veins or other factors
such as earthquakes.
.
Now let us consider these things using a few
sketches.
Let us consider a gravity dam the
weight of the dam; I label that here using
W subscript dam.
Then we are going to have
the weight of water and I have labeled that
on the left using not the weight of water
actually; the water pressure on the dam in
this one I have used the symbol W subscript
water.
And then we are going to have an uplift force
because of the presence of water on
the left of the dam, and I have used U for
the uplift force.
So, these are actually the three major permanent
loads that the dam has to transfer to the
foundation.
In addition to it, we are going to have a
bunch of incidental loads.
And the
first one that I have considered here is the
inertial load for instance because of an
earthquake.
And this particular inertial load is going
to be typically a multiplier times the
weight of the dam.
This is a very simple approach that I am discussing
here.
There could
be other more involved approaches.
The factor K depends on how strong is the
earthquake.
So, if the earthquake is very strong then
you are going to have a large value of K.
It
could go up to say 0.3 or 0.4 or 0.5 even.
If you have got a smaller earthquake then
k is
going to be much smaller; typically k could
be 0.1 or 0.05 or that kind of number for
smaller earthquakes.
Then in addition to it we could have a dynamic
water pressure
.because of earthquakes or because of water
waves caused by strong winds within the
reservoir.
So, these are the incidental loads a few of
them anyway that needs to be
transferred to the foundation.
.
Now let us look at the failure mode; the second
important consideration is the failure
mode.
Now first failure mode and this is perhaps
the most important one is scouring and
piping.
If there is a pathway for seepage to take
place across the body of the dam, then
particularly in case of earth dam or embankment
dams if the velocity of water flow
becomes too high.
Then it is going to wash out material that
comprises the dam body.
And as a result the entire dam may fail.
This type of phenomenon is called scouring
or
piping.
Then there could be liquefaction; liquefaction
could be triggered statically or during an
earthquake.
For instance, if the speed of construction
of a dam is too high, then the
weight that is imposed when the embankment
is being constructed.
The weight is
transferred to the soil underneath, and if
the foundation soils are saturated then the
pore
water pressure the weight of the embankment
is transferred immediately to the pore
water.
And as a result the pore water pressure increases.
And if you recall from our
discussion on effective stress, the increase
of pore water pressure is going to lead to
a
reduction in effective stress.
.And consequently, the strength that can be
mobilized by the soil mass also decreases.
And this may actually lead to failure, and
this type of failure is called failure because
of
static liquefaction.
The third type of failure mode is sliding
failure and here what
happens?
The lateral pressure because of the retained
water or because of the retained
tailings mass becomes too great.
And as a result, the dam slides downstream;
that is
another failure mode.
There is another failure mode called overturning
failure.
In this case because of the
lateral pressure, the dam tries to tip over
towards the downstream side by supporting
its
weight at the toe of the dam.
Let us draw a few sketches here.
So, let us consider a
gravity dam, and here let us say we have water
out here.
So, in case of sliding failure we
are going to have the dam sliding downstream
like this in this manner.
And in case of
overturning, what we are going to have is
the dam tipping over in this manner.
So, this one here we are going to call overturning,
and this one we are going to call
sliding.
Then there could be deep seated failure which
actually will lead to the
development of a failure surface through the
foundation soils underneath the dam.
Then
there could be distress because of stress
concentration when the dam tries to transfer
the
load to the underlying soil or bedrock.
The stress could become too high, and that
might
trigger failure or it might trigger inordinately
large deformations, or there could be slope
instability like this.
Let us consider an earth dam.
.
.Let us consider an earth dam like the one
we have shown in this sketch a few minutes
back.
So, here the water is on your left, and this
particular dam actually may be affected
by stability of downstream slope or the upstream
slope also may become unstable.
And it
may actually slide into the reservoir, and
the downstream slope may become unstable
and slight downwards like that.
So, it may actually lead to the failure of
embankment
dams if the stability in all types of loading
cannot be assured.
.
Then we consider load transfer.
The major points to consider here include
whether there
is bedding or fractures or faults or shear
zones.
And what is the orientation of these
planes or weaknesses with respect to the direction
of the water flow, whether they are
dipping towards the upstream side or horizontal
or dipping towards the downstream end.
Then we also need to consider the direction
and the location of load transfer.
We are
going to look at the relative direction of
the resultant that is imposed on the foundation
soils.
And what is the orientation of these resultants
with respect to the planes of
weakness that we might have within the foundation
rock.
So, let us consider those things
in the following.
..
So, if you have got bedding planes or laminations
or joints which are normal to the
resultant, we are going to have a situation
which is relatively better.
If on the other hand
the bedding planes or laminations or joints
are parallel to the resultant we are relatively
worse off.
And why that is so?
That is because from our previous discussion
it is
apparent that strength for the rock mass that
is underneath the dam is going to be the
maximum if the rock mass is loaded perpendicular
to the planes of weaknesses.
And the
strength mobilized is going to be minimal
if the rock masses are loaded parallel to
the
bedding planes.
So, these are the reasons why we want to have
in an ideal situation the orientation of the
bedding place or orientation of the planes
of weaknesses perpendicular to the direction
of
the resultant of the load that is imposed
on the rock mass because of the dam and the
reservoir.
..
So, that is illustrated in this particular
sketch; this is again the same gravity dam
that we
considered earlier.
Now here we have got the resultant parallel
to the direction of the
bedding planes of the jointed rock underneath
the dam body.
It is obvious that this type
of loading with respect to the direction of
the jointing of the rock is going to be the
worst
possible scenario, whereas in this particular
case the planes of the joints are roughly
perpendicular to the direction of the resultant.
And by the way by resultant what I mean
is the vector sum of all the temporary and
permanent loads that are being transferred
by
the dam to the foundation.
So, in this case we have got the resultant
of all the forces to be
transfer to the foundation perpendicular to
the bedding.
So, here we are much better off
in this configuration, alright.
..
The second aspect with respect to heterogeneity
of the rock is whether or not are the
structural within the bedrock whether there
are folds or not within the rock underlying
the dam.
So, what we want to have actually is that
the resultant is normal to the axis of
the fold.
If you recall our earlier discussion, the
axis of the fold in this case is like that.
So, this is the axis of the fold.
So, if we have the axis of the fold perpendicular
to the
direction of the resultant, then we are better
off.
And if the resultant is parallel to the axis
of the fold, then we are relatively worse
off.
So, in this particular configuration we are
somewhere at an intermediate situation, but
since the dam axis is parallel to the axis
of the fold, this configuration is not considered
the most optimal siting of a gravity dam.
Now why that is so?
That is because if you
recall our previous discussion on folding,
the stress concentration within the rock mass
is
maximum at the crown of the fold and at the
bottom of the fold.
So, this one here; these
are two locations where you are going to have
large stress concentrations.
Large stresses
and if on top of it you apply the resultant,
then the stresses within the rock mass at
these
locations where the stresses were very large
to begin with; that might actually trigger
larger deformation or even local dislocation
within the rock mass.
So, this is the
fundamental reason why we want to orient a
dam in a direction perpendicular to the axis
of the fold, okay.
..
Then we move onto dams in a faulted terrain.
So, the considerations are almost the same
here as we did in case of tunnels in the previous
lesson.
So, what we want to do is to
avoid sites underlying by active faults.
Then we want to place the resultant normal
to the
fault plane, because fault plane here is a
plane of weakness.
And we want to actually
place our resultant perpendicular to the plane
of weakness in order to derive maximum
strength mobilized in order to make it possible
that maximum strength is mobilized.
Then the weight of the reservoir and the dam
could actually lead to a large readjustment
of in-situ stresses.
And this might induce seismicity, and such
type of earthquakes is
called reservoir induced seismicity.
You also need to consider while siting a dam
in
faulted terrain is that fractured rock near
fault could provide pathways to water seepage.
And this in fact has led to dam failures in
the past; we are going to discuss this in
detail a
little bit later on.
Now these jointed rock mass or fractured rock
mass in the vicinity of the faults need to
be either excavated or replaced, or they need
to be grouter in order to preclude water
flowing past underneath the dam through the
foundation.
So, these are the major
considerations that one needs to satisfy while
siting a dam in a faulted terrain.
..
Now we look at a few cases histories involving
failure of dam.
The first case history that
we consider here is that of Austin Dam, and
this particular dam failed in March 1990.
This is a dram across the Colorado River in
southern United States near Austin Texas.
This dam was founded on shale and limestone
bedrock.
Now what happened?
The dam
washed out during a high flood in March 1990
because of slippage through the shale
bedrock.
And the dam, in fact, washed out quite a ways
downstream of the original
location of the dam.
The second failure that we consider here is
that of the failure of St. Francis Dam.
So, in
fact, let me highlight here before I move
on with St. Francis Dam that the failure of
the
Austin Dam is one of the failures because
of sliding.
Then as I stated earlier that failure
could also be because of scouring and piping.
Saint Francis Dam, in fact, was another
dam that failed because for seepage and piping
and scouring.
And this particular dam is
another embankment dam, and it was cited on
a site underlying by a very steeply dipping
fault perpendicular to the dam axis separating
conglomerates and mica schist.
What happened?
The conglomerates were badly fractured because
of the presence of
fault, and you can also imagine that conglomerates
by their inherent nature are composed
of coarse grained particles.
As a result they themselves could be quite
permeable if they
are well compacted, and here we have got fractured
conglomerates.
So, this particular
.rock mass was prone to seepage and the seepage
through conglomerates actually washed
out a portion of the dam in March 1928.
And this led, in fact, to the failure of this
dam.
Both these dams both Austin Dam and St. Francis
Dam; both these dams were
constructed as embankment dams, but you could
have similar problems in case of other
dam types such as gravity dams.
And you need to design the dams in such a
manner that
such possibilities are, in fact, precluded;
it can be totally avoided.
Of course, in case of
gravity dams you would not have to consider
the possibility of seepage and piping,
piping and scouring, but the possibility of
seepage has to be addressed in case of gravity
dams as well, okay.
.
Now a couple of other case histories involving
dam construction in India.
First of all, we
consider Obra Dam.
This dam is a gravity dam constructed across
river Rihand near the
border of UP and MP in the southern fringes
of Uttar Pradesh.
And this particular dam is
sited in an area which is underlying by limestones.
And you can imagine that if there are
limestone’s which are soluble; un-compacted
limestones are quite soluble.
And such
limestones actually could develop caverns
and cavities within the rock mass because
of
their solubility, and this type of terrain
is called caustic terrain.
So, Obra Dam was constructed in a terrain
underlying by cavernous limestone.
And what
happen?
In cavernous limestone seepage through foundation
becomes a very major issue
that might jeopardize the functionality of
the water retaining dam and the reservoir
that it
.is suppose to create.
Now in order to preclude seepage in this particular
case, heavy
grouting was undertaken and grouting had to,
in fact, go to a depth of as large as 75
meters to tie in the bottom of the dam with
the underlying impervious shale bedrock
underneath the cavernous limestone unit.
The second case history that we consider here
is that of Nagarjuna Sagar construction.
So, this particular dam was crisscrossed by
several low angle reverse faults in gneiss
and
granite bedrock.
And because of that fact that fractured gneiss
and granite could be
weathered, because of excess of water they
could be weathered.
And they might actually
more often than not, they become quite soft,
and several such soft areas were identified
underneath the foundation of the Nagarjuna
Sagar gravity dam.
And these pockets had to
be excavated and replaced before the construction
of the dam in order to ensure that the
dam is founded on sound rock mass.
.
Now we move on to bridges; first we consider
type of bridges.
This is basically a slap
type bridge.
So, what you can see here is the water cores
are here.
So, this is the water
cores, and these are the abatements, and the
bridge deck is here.
Now there could be
other types of bridges such a frame bridges
like the one that is shown; you should also
notice that there are orange arrows in these
sketches that indicate the direction in which
the load is transferred by the bridge superstructure
to the foundation soil or rock.
This is
an example of arch bridge.
..
This one is an example of beam and cantilever
bridge.
.
And this is an example of cable stayed bridge,
and you should notice in all cases
carefully the direction in which the loads
are transferred.
..
So, the considerations here are essentially
the same as we did in case of dam
foundations; only thing that you need to consider
here in addition to it is that the loads
are transferred within a relatively smaller
area to a larger depth.
As a result, the bridge
foundation is affected more significantly
because of heterogeneity in soil and rock.
So, a
very thorough subsurface geotechnical investigation
is a must at the location of all the
abatements and foundations before a bridge
construction can be taken up.
If the
investigation is inadequate or does not go
to sufficient depth, the bridge construction
would have to encounter inordinate delay because
of constructability problems.
.
.Then road cut; if a road cut is constructed
parallel to the strikes of planes weaknesses,
and if we have got dipping inside the cut,
then there could be potential for instability.
And if the dipping is outside of the cut,
then the road cut is going to remain relatively
stable.
If the road cut is normal to the strike, stability
is better.
There are other
considerations such as weathering of bedrock,
because of the road cut you might actually
given entry pathways of water entry through
the planes of weaknesses into the rock mass
that might trigger chemical weathering.
Creep is another issue that needs to be accounted
for during construction of a road cut as well
as the possibility of falling rock from the
top
of the road cut.
.
Rock fall countermeasures around road cuts,
we can try to intercept the blocks of rock
that might actually mobilize down slope.
We could have a catchment ditch near the base
of the rock.
We could have cladding on the slope face in
form of metal nets shotcrete
facing, or we could have fencing parallel
to the road cut parallel to the slope.
These acts
as barriers and intercept the falling rock
or other debris or we could install bolting
to
secure potentially unstable rock mass on the
slope face.
..
So, we now summarize this particular lesson.
What we learnt here are major geological
considerations in the construction of dams,
roads and bridges.
We also looked at some
cases histories to illustrate the geologic
considerations in dam, and we looked at a
list of
rock fall counter measures.
.
Finally, we wrap up this particular lesson
with a question set.
The first question is, is it
desirable that the resultant load we transferred
to the foundation underneath a dam be
directed perpendicular or parallel to the
planes of weaknesses?
Provide reasons.
What are
.the key points to be considered while planning
a geotechnical investigation program for a
bridge?
And how rock fall hazard on a highway adjacent
to a cut slope can be mitigated?
Try to answer these questions at your leisure.
When we meet with the next lesson I am
going to provide you my version of these answers;
until then bye for now.
Thank you.
.
