- SUBMITTED BY
- RAJMANI SUBEDI-056/BCE/102
- RATNESH MISHRA-056/BCE/105
- SACHINMAN SHRESTHA-056/BCE/106
- YOGESH PAKHRIN(LAMA)-056/BCE/143
|
- SUBMITTED TO
- DEPARTMENT OF GEOLOGY
- INSTITUTE OF ENGINEERING
- PULCHOWK CAMPUS
|
ACKNOWLEDGEMENT
The geological field knowledge and field visit is very important especially for a civil engineer.
The main work of a civil engineer is to study the feasibility of the constructon and stability of
structures in different types of land feature including rock, their slope, riverside and clayey
portions. Literature alone cannot assist in producing any satisfactory results. Therefore a
thorough knowledge of actual field visit counts for its credit.
As the geology deals with rocks and stones along with their origin including types of soil,
strike, dip-direction and other geological discontinuities such as faults, folds, joints,
landslides, use of topography map for proper location of site and other activities. It is
therefore very essential to make a field visit. From the field visit we came to know much about
structural geology including the above mentioned features.
For the basic knowledge of field work of structural geology the three days from 14th of Poush
to 16th of Poush we were taken to Malekhu for geological excursion. This performance was very
effective for the partial fulfillment of knowledge and experience. However the three days of
tour was not sufficient to fulfill the requirement,
We are very grateful for the teachers and lecturers who helped us during the field trip and
tought many impotant things within the limited time period.
CONTENTS
1.Introduction
1.1Objectives
1.2Methodology
1.3Instrument
2.Geology
2.1General geology of Malekhu and adjacent area
2.2Major rock type
2.3Major Geological structure
2.4.1Benighat slate
2.4.2Malekhu Limestone
2.4.3Robang Phyllite with Dunga Quartzite
2.4.4Radua formation(Garnetiferous Schist)
2.4.5Bhaisedoban Marble
2.4.6Gneiss(Kulekhani Formation)
2.5Engineering Geological comments
3.Study of river Morphology
3.1Types of river channel
3.2 Erosional and Depositional features of the river
3.3 Constructional material survey from river deposit
4.Study of landslide
4.1Study of different landslide during the field trip
4.2.1Landslide no:1
4.2.2Landslide no:2
4.2.3Landslide no:3
4.2.4Landslide no:4
4.2.5Landslide no:5
4.3Landslide stability analysis
5.Rock mapping
5.1Introduction
5.2Stereo photography
5.3Scan Line Survey
5.4Rock map of the outcrop at the site
6.Conclusion
1. INTRODUCTION
1.1 GENERAL INTRODUCTION
The Geological field excursion was organised by the Department of Geology under Institute of
Engineering, Pulchowk campus in order to aquaint knowledge about the geological structures, their
engineering significance , distribution of different rocks and soil types. The time duration
being three days from 29th to 31st December 2001 was spent in geological field study in Malekhu
situated 75 kilometres west of Kathmandu.
1.2 OBJECTIVES
The main objectives of our field visit was:
-Measurement of dip and strike
-Study of bedding foliation
-Handling of compass for documentation of Engineering geological data
-Study of landslides
-Study of morphology of river channel
-Rock identification in the field
-Identification of geological units of the Lesswer Himalaya and Kathmandu Nappe
-Engineering geological studies along the large scale geological discontinuity (The Mahabharat
Thrust)
-Study of the rock slope along the road corridor
-To know the rock mapping techniques of the rock outcropt
1.3 METHODOLOGY
The common methods used in the geological excursion were the site selection and the field
observations. Different places suitable for the geological study was selected and their location
was determined by the map and the observation related to such structures were taken and copied
such as physical appearences, orientation, geological structures. Photographs were taken at many
sites. In some, scatches were also plotted to assist the better understanding. In still some
cases graphs were also plotted like in rock outcropt observation.
1.4 INSTRUMENTS
The various instruments used in the field study were hammer, geological compass and measuring
tape.
(i) Hammer
A hammer was used to test the hardness of rock in the field. It was performed by striking the tip
of hammer and the surface of the rock whose hardness was to be determined.
(ii) Geological Compass
A geological compass was used to measure the attitudes of the geological structures. The compass
was mainly used for measuring the bearing of object with respect to north, to measure attitudes
of geological structures such as strike and dip of planes, plunge and trend of lines, to measure
slope orientation.
The commonly used geological compass during the field visit were Clinometer and Brunten Compass.
The main operation of geological compass consists of opening the compass carefully, levelling the
spirit level and placing the compass on the planer feature to me used for measurement.
(iii) Measuring Tape
A measuring tape was used to measure the distances between different discontinuities such as in
the outcropt of rock strata.
3 MORPHOLOGY OF RIVER
3.1 INTRODUCTION
ALmost 71 percent surface area of the earth is covered with water in the form of rivers seas and
oceans. Water in its liquid forms is the most important geoligical agent that modifies the
surface morphology of the earth on a very large scale.
The geological work performed by water as a body of running water is mostly in the form of rivers
and streams.
MORPHOLIGY OF RIVER CHANNEL
Appearance of river channel and the study of its external fature is known as morphology of river
channel. In most cases the tendency of river is to flow towards the sea. The highland or the
mountainous regions from where the river originates is called its head region. From the head
region, the river flows through gradually decresing slopes and then through almost flat lands
before it actually empties into the sea. The place where a stream or river empties into the sea
is called its mouth.
Based upon its morphology river channels could be divided into
- Straght
- Meandering
- Braided
(a) Straight river channel
This kind of river channel has its flow of water in straight form. This is mostly possible in
hard rocks. Presence of fault changes the course of flow of river channel.
From head to mouth, a river may exhibit a variety of geological activity. This is head region, it
flows with roaring speeds acquiring energy by virtue of which it is capable of cutting down even
the hardest rocks along and across its course.
(b) Meandering River Channel
-River channels in which the course of the river is bent towards different direction within small
area
-Mostly possible in soft rocks
-In middle reaches, the river becomes mature.
It has alresdy acquired some load to carry down and the capacity to cut vigorously is gone. It
does erode but only selectively, changing its course where it finds obstructions which are
insurmountable. It meanders profusely, i.e. changes its course again and again through a small
area.
It flows in loops.
Menders are therefore typical character feature of a mature river.
(c)Braided River Channel
-Rivers in which flow of water is along different channel along different channel within the
same river, are said to have braided river channels. This type of river channel is generally
present in the flat lands near its mouth, where the river behaves like an old organism: just
moving ahead to join the parent body of all the waters, the sea, in a majestic manner: without
noise and in full compusore.
EROSIONAL AND DEPOSITIONAL CHARACTERS OR RIVER CHANNELS
Before talking about the erosional and depositional characteristic of the river channels, let us
see on what factors the rate of river depends.
Rate Of River Erosion
The capacity of strems to performerosive work depends on the following main factors:
(1)Velocity
Fast moving streams are capable of exerting greater pressure on the channel rocks and cause
stronger impact bu the course tools. A high velocity enables the stream to carry all the load it
acquirea easily so that still some erosive power is left. The quantity of tools that can be
carried by fasret streams being more, their broading capacity is also increased considerably.
Thus other things being the same, greater the velocity of the stream, higher is its erosive
power.
The velocity of a stream itself depends on
(i) The gradient of the channel
(ii) The volume of water in the stream
(iii) The nature of the channel (whether rough or smooth) and
(iv) The load of sediments in the stream at a given point of time.
(2) Lithology
This signifies the nature of rock along the river bed and sides. Some types of rocks are more
easily eroded by stream water than the other exactly identical eroding conditions. Thus,of a
limestone and sandstone forming bed rock of a stream and lying side by side (at the same
gradient), limestone will suffer erosion at a higher rate compared to sandstone. This is because
limestone have a lower hardness and a chemcal composition favorable for solvent action of water.
(3) Load
If a stream is fully loaded i.e. it is incapable of taking any furter load, then the tendency to
erode the rocks of the channel will be correspondingly reduced. Its major power is used in
transporting load on the contrary an unloaded stream can erode the rocks more effectively.
Now the erosional and depositional characteristic of river channels can be summerised as below:
(a) Straight river Channel
In this type of river channel, deposition is not possible. It is associated only with erosion.
The gradient of straight river channel is quite high and discharge is quite low.
(b)Meandering river channel
The gradient of mendering river channel is quite low which increases the possibility of
meandering. The discharge is quite high which also contributes to meandering of a river. In this
type of river channel, erosion and deposition are frequent and approximately equal.
(c) Braided River Channel
Amount of discharge varies accordingly to the season in such river channel. Braided river channel
account for more deposition and less erosion i.e. depositionis predominant over erosion
DEPOSITIONAL MORPHOLOGY
Deposition by rivers:
When water carrying the load losses its every material starts to deposit i.e. deposition takes
place at a place of energy loss. Thus the phenomenon of dropping down of the load by any moving
natural agent is called deposition; resulting accumulation of the load is its deposition.
There are basically three factors sufficient to determine the trend of process of deposition by
streams. They are
(i)energy
(ii)environment
(iii)time
Thus,if energy available to transport the load
decrease,then a part of the load can no longer be
transported.Its deposition thus becomes inevitable.The
decrease in energy may take place due to reduction in
velocity(as when a stream enters from a steep to
gentle gradient)or due to reduction in volume(as
during dry spell in the same area.
Similarly the factor of environment influences
deposition through configuration or shape of the
channel.Irregular surfaces of the channel represent
such areas which tend to reduce the velocity without a
change in gradient or volume of water.
The factor of time operates through the above two
factors.That when a stream would drop down the load it
is carrying will be determined by a general
statement"whenever its velocity is appreciably
checked".
Precipitation of dissolved load is another process
contributing to deposition.This takes place where
there is an appreciable change in the physico-chemical
conditions attending the stream water.
Types of Flluvial Deposits:
Deposits laid down by running water are called
alluvial,flluvial or fluviatile deposits.Such deposits
differ greatly in size,shape and mode of
origin.Following are some chief types of stream
deposits:
1)Alluvial Fans And Cones
These are cone shaped accumulation of stream debris
that are commonly found at places where small
intermittent streamlets coming down from hills enter
the low lands.The apex of such a deposit points up
hill and its slope may range from almost flat to as
much as 50.
When the slope of the deposits is below 10,the
alluvial deposit is known as alluvial fan,and when it
is from 10-50,the deposit is known as alluvial cone.
Alluvial fans and cones show contrasting patterns in
distributon of fragments and particles of various
sizes at their apices,peripheries and in the main
body.Further repeated accumulations over an initial
fan or cone contributes to its considerable
growth.Alluvium is usually very porous and will be
compressible if rich in clay and permeable if composed
of gravel,sand or silt.
2)Flood Plain Deposits
Flood waters are invariably heavily loaded with
sediments of all types.When these waters overflow the
banks and spread as enormous sheets of water in
surrounding arears,their velocity gets checked
everywhere due to obstructions.As a consequence they deposit most of the load in the form of a
thick layer of mud,so
commonly seen after major flood.Since such a process may get repeated year
after year,the low lying areas surrounding major rivers are actually made up
of the layers of mud deposits laid after a number of floods.These are
generally level or plain in nature and extensive in area and are called Flood
plains.All the plain around major rivers are actually flood plains.These are
invariably very fertile in nature and hence have been supporting population.
Two major types of flood plains known as Convex flood plains and flat
flood plains are known.
3.DELTAS:
Deltas are defined as alluvial deposits of roughly triangular shape that
are deposited by the rivers at the points where they enter into the sea.This
term was first used by Herodotus for the deposits of the river Nile at its
entry into the Mediterannean Sea.
Deltas are very complex in their structure.A number of fracture are
involved in their formation,evolution and modification.
4.CHANNEL DEPOSITS:
Many streams are forced to drop a part of their load along their
beds,especially in the flatten regions along their course.Most commonly the
deposits so formed take the shape of long narrow rigides called bars,since
these are commonly made up of sand,they are reffered as sand bars.Very often,
the sand bars are temporary in nature because with an increase in velocity,the
river mass cut them down(erode) and take the sand along with it to deposit it
at new place.Small landform in the channel of the river is called a Channel
bar.
Construction material from River.
River is the most important source of construction such as
sand,gravel,clay,aggregate and dimension stone.These material may be used in
their raw state for construction.Being a natural source,river in the most
widely used source for excavation of construction materials and also the most
cheapest one.
The presence of rivers close to the site makes the use of construction
material much cheaper than a manufactured alternative such as concrete and
also with some thoughts,the design of the structure can be changed so as to
make use of the available materials.This is a common practice in the
construction of large structure such as embankment,roads and airstrips.To
correctly assess the potential of economically available raw materials,it is
necessary to appreciate both their geological character and their mode of
formation.
Rivers are sources of the construction material as explained earlier.So
the available deposits of gravel and sand which occur in the terrace gravels
are excavated on a large scale for supplies of aggregate and sand for concrete
and mortar.Alluvial mud may be used as one of the raw materials in the
manufacture of cement by mixing mud with limestone in the required proportions.The construction
sand is taken from the deposited bank.
4.STUDY OF LANDSLIDE:
INTRODUCTION:
It is a natural phenomenon in which the slip surface looses its component, thereby causing
excessive destruction to the nearby surrounding.Landslide is different from erosion in a way that
eroded slope are created by the movement of air,surface water and the sea.The quantities that are
capable of loosing dislodging and carrying particles of the soil,sediments and larger pieces of
rocks are described as the agent of erosion.
Thus landslide can be found in the following ways.
1.By determining the crown and tow:crown is the uppermost part of the
landslide whereas toe is the lowermost part of the landslide.The material laying between these
two surfaces is carried towards the tow.(fig 2)
2.By determining shear stress of the soil sample from the expected region.For
this purpose we take the soil samplefrom the land of expected region and carry out the test to
find the shear stress which is given by --T=c+6tanQ----change it-----,where c and Q are shear
paramater.Thus we see that shear stress depends upon c and Q ,which are found experimentally.
3.Geophysical study:We can also find the slip surface by inducing physical
energy and observing the response of the material of the landslide of the expected area towards
that induced physical energy.
4.Drilling:Slip surface can also be found out by drilling exist.They are core
drilling and drilling.
CAUSES OF THE LANDSLIDE
Causes of landslide are primarily classified into static and dynamic causes;
STATIC CAUSES OF LANDSLIDE:
1.Material:
Highly weathered rock formed by chemical decay process and mechinical disintegration
increases the possibility of landslide.Presence of boulder mixed soil which bring about further
fracture in the rock structure and thus caused landslide.
In phylitic rock,presence of mineral such as talc,graphite,chlorite and even micas on the
surface along the rock resulting in landslide.
2.Slope Angle:
If the slope angle is greater than the angle #,it is said to be unstable.Thuse a slope which
has steeper slope,i.e,more dip,have more chances of landslide.For stable surface,# is mostly less
than 40 degree,but if reverse exsist then the surface is said to have unstablle slope and
landslide is more prominient in such place.
3.Pore water pressure:
Shear stress is also given by the expression T=c+(6-Q)tan#,where Q is the pore water
pressure.Excessive rain fall causes cracks in the crown,thus clearing the passage for entry of
water through it.Water also entersthe soil pores from underground.In addition to all these
water,there is pre-existance of water in the soil pores.Presence of all these water results in
the stability of the soil structure or rock structure because in such a condition,the driving
force(dF) become greater than the resistance force(RF) ond normal stress reduces leading to the
occurrence of landslide,i.e.safty factor dF/RF>1.
4.Construction:
During road construction,the toe of the road structure or soil structure is out ,i.e it is
greater than 40 degree, which leads to landslide.However this can be resisted by construction of
retaining wall.
DYNAMIC CAUSES OF LANDSLIDE
1.Vibration:
Due to the movement of the loaded vehicles on the highways,there is certain amount of ground
vibration always taking place which reduces the stability of the nearby rock or soil
structure,resulting in landslide.
STUDY OF DIFFERENT LANDSLIDE DURING THE FIELD TRIP
During the course of this geological fieldwork,we
visited some sites of landslides which helped us
immensely in learning about its features practically.
Below are the sites of landslides visited by
us.The explanation of some striking features of the
individual landslide wherever required along with their
photographs are also given alongside.
SITE 1
I t included three landslides,with only two having
practical significance.The third one being only a
scarp.Since there was no main body in htis supposed
landslide,it was called a landslide scarp.
1st landslide
Features:SAME AS EXPLAINED EARLIER
2ND LANDSLIDE
Features
It actually consists of two landslides as there are two
scarps.In this landslide,the orientation of its planar
features are in unfavourable direction to its slope.Nature itself has brought this landslide with
cause,and solution of this type of landslide being same
as explained earlier.
2)Site 2(Ranagaun)(Refer Fig 3)
Features:
It is an old landslide,the evidence of which being the
presence of completely weathered rocks,loose soil
etc.Since houses have been made below the area of
alndslide,safety is very less,as there is evry
possibility of another landslide at this place.
However,the village residing in this landslide affected
area can be protected to a certain degreee by control
drainage.
SITE 3(JugeKhola) (fig4,5)
It is a highly landslide affected area.
Presence of six landslides with each having its own slip
surface.
SOLUTION:
Removal of debris alongside JugeKhola is not the
solution.Even tunneling is very dangerous at this place.
The only solution for this landslide is cut and fill i.e
remove some part of the landslide from one side and fill
some on the another side.
SITE4 (FIG6)
Landslides also bring with them the debris i.e the
boulder and fine sized particles.Such debris is called
landslide debris.The information about debris plays an
important role in design of bridge.While designing a
bridge one should look for the followinf things:
a)Site Selection:A site for the construction of bridge
has to be selected.
b)Flood Level:The flood level or water level during
times of flood in the river upon whiach the bridge is to
be made should be found out.
c)Debris Potentiality:
The most important aspect of bridge designing is the
determination of debris potentiality in the river upon
which the bridge is to made.The size of the debris i.e
whether it consists of finer or boulder materials should
also be taken into account,along with the calculation of
its amount.
5)FIG 7 AND 8
It consists of two landslides.The first one ahving
vegetationon the inclined surface.This has been made
possible by taking slope protection measure and slope
stability measyre such as construction of the retaining
wall and anchoring.
Second Landslide
It consists of less weathered rocks and weathering has
taken place along the planar feature.It has occurred as
the orientation of discontinuity is unfavourable to the
dip directionand the dip amount.The slope of the surface
is very steep.
The palce can be protected by anchoring and bolding.
4.3.LANDSLIDE STABILITY ANALYSIS
(a)Retaining wall:Retaining walls can be constructed at the landslide expected
area.However it is costly.Even then it should be constructed at the place which do not have
differential movement.
(b)By reducing Q:By bringing about reduction in pore water pressure(Q) also,we can avoid
landslide.
(c)Construction of surface drainage from the area behind the scarp :We should construct
surface drainage from the area behind the scarp so that water does not enter into the crack and
thereby also does not affect the pore water pressure.The drain should however be maid above the
crack for this purpose.
(d)Avoid disturbing mechanical equilibrium condition:Landslide occure due to disturbance
in mechinical equilibrium.Thus one should avoid doing such a thing so that pore water pressure
does not develop.
(e)Construction of Gabonian wall:Gabonian wall should be constructed at the place of
differential moment.If retaining wall is however maid ,it will be waste of money.Gabonian wall
can also be constructed at a place which have developed pore water pressure.At a place where pore
water pressure exist,a small hole should be made before construction of gabinian wall.
Though most of the reasons given above for the occurance of landslide are true,some may
be stated otherwise.for eg.It is not always true that construction of road results in
landslide,Sometime nature itself may bring about devastating landslides.
In addition to above stated things one should also know certain important features of
landslide.When we look at the place of landslide,if we see too many scraps, we can conclude that
many landslide may have been gone at that place.Age of landslide can be recognized by the degree
of weathering of the rock at the place of its occurrence.
5 ROCK MAPPING
5.1 INTRODUCTION
The main purpose of the rock mapping for much of its history has been reconnaissance mapping of
large regions whose geology was essentially unknown. The general geological framework,
essentially what rock is where, has now been established, and the work of the rock mapping is now
directed more towards the understanding of the cause and effect, and sequence of geological
events. This entails many studies in addition to geological mapping, such as data compiled from
geophysical and geochemical surveys as well as from remote sensing. Yet the relevance of such
studies remain strongly dependent on accurate geological mapping. The resultant geological maps
contain much more information than the simple distribution of rock types, and are essential in
revealing favourable areas for mineral exploration, fossil fuels (mainly coal, oil and gas), and
identification of potential geological hazards
Information is gathered through geoscience field surveys and from industry assessment reports
filed in compliance with legislation. The inventory is used to attract industry investment, to
assist government's stewardship of its rich mineral resource endowment, and to help manage and
protect Crown Lands.
The main activities include: geological and geochemical surveying; mineral, coal and industrial
mineral inventories management; mineral potential assessments for land use planning; monitoring
exploration activities; assessing geological hazards; publishing maps and reports; and providing
geoscience expertise to support government's sustainable development objectives.
Conclusively Rock mapping (geologic maps) is the plotting of target formations and
terraines on maps or areial photographs for later compilation.
STEREO PHOTOGRAPHY
Stereo photography is the practice of having successive [aerial] photographs overlap the next by
55%-60%. This pair (known as a stereo pair) is used with either a stereo viewer, stereoplotter,
or digitized
for use with soft-copy stereo programs to view the desired area in three dimension (3-D).
It may surprise you to hear that the hype of stereo photography was 100 years ago,
in the late 19th centuary.The stereo photography helps effectively in rock mapping by providing
clear 3D image of the rock.Dip directoin ,dip amount and strike can be found from the photograph.
About 2km north from Malekhu bazar ,two photograph of the rock outcrop has been taken
simultaneously from the same point at a distance of 7.5km away from the site.(2 photos are
attached below).
SCAN LINE SURVEY
Scan line survey is a sampling technique whereby information is detailed along a single pass of
the recording device. The process is repeated at intervals to cover the desired area.
Scan Line Survey is mostly used in engineering structure.The discontinuities which impart the
loss of strength of the rock are found out by this method.This survey is carried out on the road
alignment before its construction.
The rock outcrop has been surveyed for the different structure feature of the rock massOn the
total span of 10meter the survey was carried out at the level of the road and 1meter high from
it.Following are the geological engineering data collected at the site.
Rock type:Schist,Phyllite.(metamorphic)
Weathering:Moderately weathered
Distance(m) |
Dip amount(`) |
Dip direction(`) |
Joint/Foliation |
FIRST LINE |
0.5 |
76 |
N8E |
F |
2 |
76 |
N8E |
F |
4.75 |
80 |
N86E |
J1 |
5.1 |
76 |
N8E |
F |
5.15 |
27 |
N40E |
J3 |
SECOND LINE |
0.65 |
76 |
N8E |
F |
2.25 |
76 |
N8E |
F |
3.6 |
76 |
N8E |
F |
3.75 |
81 |
N86E |
J1 |
5.85 |
26 |
N40E |
J3 |
6.6 |
7.15 |
N74 E |
J2 |
THIRD LINE |
1 |
76 |
N8 E |
F |
1.45 |
80 |
N85E |
J1 |
3 |
76 |
N8E |
F |
4.2 |
50 |
N74E |
J2 |
5.15 |
76 |
N8E |
F |
7 |
76 |
N8E |
F |
7.6 |
26 |
N40E |
J3 |
9.5 |
76 |
N8E |
F |
The general attitude of the rock mass is:
Dip direction:N42`E
Slope amount:65`
Characteristics of the planer feature:
1.Roughness:
J1-Rough J2-Rough J3-Rough
2.Opening:
J1-Open J2-Close J3-Close
3.Infilling:
J1-Clay J2-Clay J3-Clay
4.Ground water condition:
J1-Dry J2-Dry J3-dry
5.Intact Rock:Moderately strong
6.Continuity:
J1-110cm J2-20cm J3-15cm
STUDY OF THE OUTCROPT AT THE SITE
The rock map of the outcrop can be obtain by joining same joints and foliation plane obserbed at
different point of the rock outcrop.The obserbed point can be plotted on the graph.
CONCLUSION
This geological field trip to Malekhu was organized to provide the practical knowledge of
geology to the students.The geological field trip to Malekhu aimed to provide the acquaintance
and knowledge of geological element and their proporties as well as features.The scope of field
study outlined before were fully met with the co-operation of the faculty member and Malekhu
posses wonderful geological diversities and almost all type of the rocks,structures,and
grological factors like rivers, hills ,slopes, sedimentation etc , were available to study within
a small area.
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