IntroductionAlmost every remote sensing exercise will require
field surveys at some stage. For example, field surveys may be
needed to define habitats, calibrate remotely sensed imagery (e.g.
provide quantitative measurements of suspended sediments in surface
waters), or for testing the accuracy of remote sensing outputs.
This chapter aims to describe some of the key generic issues that
must be borne in mind when planning a field survey. Specifically,
the chapter sets out the general considerations involved in
surveying coastal habitats, describes the importance of recording
the positions of survey sites usingGlobal Positioning Systems
(GPS), and gives an introduction to the costs of field survey
(costs are explored further in The importance of assessing the
accuracy of remote sensing outputs is stressed and guidance given
on appropriate statistical methods for calculating the accuracy of
habitat maps. Specific coral reef, seagrass and mangrove field
survey methods (Plate 5) are too varied to include here and are
discussed in Chapters11, 12 and 13 respectively. The need for field
survey Before the need for field survey is discussed, it is worth
briefly reviewing the concept of remote sensing. Remote sensing
provides a synoptic portrait of the Earths surface by recording
numerical information on the radiance measured in eachpixelin each
spectralbandof the image being studied. To create a habitat map,
the operator must instruct the computer to treat certain
referencepixelsas belonging to specific habitats. The computer then
creates a spectralsignature for each habitat and proceeds to code
every otherpixelin the image accordingly, thus creating a thematic
map.Historically, some researchers have looked upon remote sensing
as a means of mapping without the need to conduct field work.
Whether this is an appropriate tenet depends on the objective of
the study and familiarity of the operator with the study site. On a
general basis, most people can view a satellite image or aerial
photograph and easily distinguish different features according to
their colour,contrast, pattern, texture and context. In some
instances instances, this may be all that is required to make use
of the imagery. For example, visual interpretation is usually
sufficient to delineate the shape of coastlines. In the majority of
studies, however, the objective is more sophisticated (e.g. mapping
submerged habitats) and the thematician may not be able to draw on
visual interpretation and background knowledge to identify each
habitat type. In fact, the thematician is unlikely to be aware of
the variety of habitat types in the image. Our own experience
supports this view (seeChapter 9): even when moderately familiar
with an area (the Caicos Bank), theoverall accuracyof the final map
was low if field surveys were not conducted (e.g. 1530%).The aims
of field survey are three-fold. Firstly, to identify each feature
of interest (e. g. each habitat type). Secondly, to locate
representative areas of each feature in order to generate
spectralsignatures(spectra) from the imagery. Thirdly, to generate
adequate additional data to test the quality or accuracy of the
imageclassification(i.e. habitat map). This latter consideration is
extremely important for any mapping exercise. In a coastal
management context, imagine the legal problems in suggesting that a
developer had cleared a particular mangrove area if the accuracy of
mangrove maps were unknown. Taken a step further, where do decision
makers stand legally if offenders are fined according to the extent
of habitat that they have illegally destroyed? Legal problems may
not be the only consequence. In biological terms, management
initiatives based on a habitat map of unknown accuracy could lead
to unnecessary or inappropriate action, although it is difficult to
predict or generalise specific problems arising from such
circumstances. Surprisingly though, accuracy assessments are fairly
scarce in the context of mapping tropical coastal resources.
Planning field surveysField surveys must be planned carefully
and due consideration must be given to the objectives of the study
and the nature of habitats being surveyed. These issues will
dictate most aspects of survey design, such as the sampling
strategy, sampling technique, sampling unit, amount of replication,
time to survey (i.e. weather conditions, date of image
acquisition), ancillary data (e.g. depth, water turbidity) and the
means of geographically referencing data. Specific considerations
on methods, sampling units and ancillary data are described in the
relevant chapters of this handbook (i.e. for mapping coral reefs,
seagrass beds and mangroves) but more general comments are made
here.
Estimate costs of field surveyField surveys are expensive and
not all of the costs incurred in gathering field data and relating
it to remotely sensed data are immediately obvious. However, a full
analysis of field costs is vital when designing a remote sensing
campaign to ensure that realistic budgets and work schedules are
planned. A generalised discussion of costs is presented here.
Detailed advice on planning a remote sensing field campaign in
terms of cost and the actual costs incurred in mapping the habitats
of the Turks and Caicos Islands are given in
What is accuracy?Accuracy is referred to in many different
contexts throughout this book. The accuracy of aGPSposition fix is
a measure of the absolute closeness of that fix to the correct
coordinates, whereas positional accuracy refers to the accuracy of
a geometrically corrected image and is measured with the root mean
square (Chapter 6). This section is concerned with thematic
accuracy, that is, the non-positional characteristics of spatial
data. If data have been subjected to
multispectralclassificationthen thematic accuracy is also known
asclassificationaccuracy (Stehmen 1997). This accuracy refers to
the correspondence between the class label and the true class,
which is generally defined as what is observed on the ground during
field surveys. In other words, how much of the class labelled as
seagrass on a classified image is actually seagrassin situ.
Surveying
This article is about measuring positions on Earth. For other
uses, seeSurvey.at zero chainage at Katra to Maihar Distt. Road
A surveyor at work with an infrared reflector used for distance
measurement.Surveyingorland surveyingis the technique, profession,
and science of determining the terrestrial or three-dimensional
position of points and the distances and angles between them. A
surveying professional is called aSurveyor. These points are
usually on the surface of the Earth, and they are often used to
establish landmapsand boundaries forownership, locations like
building corners or the surface location of subsurface features, or
other purposes required by government or civil law, such as
property sales.
Surveyors work with elements
ofmathematics(geometryandtrigonometry),physics,engineeringand
thelaw. They use equipment liketotal stations, robotic total
stations, GPS receivers, prisms,3D scanners, radios, handheld
tablets, digital levels, andsurveying software.Surveying has been
an element in the development of the human environment since the
beginning of recorded history. The planning and execution of most
forms ofconstructionrequire it. It is also used
intransport,communications, mapping, and the definition of legal
boundaries for land ownership.
HistoryModern surveyingAbel Foullon described aplane tablein
1551, but it is thought that the instrument was in use earlier as
his description is of a developed instrument.Gunter's chainwas
introduced in 1620 by English mathematicianEdmund Gunter. It
enabled plots of land to be accurately surveyed and plotted for
legal and commercial purposes.
Table of Surveying, 1728CyclopaediaIn the 18th century, modern
techniques and instruments for surveying began to be used.Jesse
Ramsdenintroduced the first precisiontheodolitein 1787. It was an
instrument for measuringanglesin the horizontal and vertical
planes. He created hisgreat theodoliteusing an accuratedividing
engineof his own design.Leonard Digges, Joshua Habermel andJonathan
Sisson[4]invented more primitive devices in the previous centuries,
but Ramsden's theodolite represented a great step forward in the
instrument's accuracy.William Gascoigneinvented an instrument that
used atelescopewith an installedcrosshairas a target device, in
1640.James Wattdeveloped an optical meter for the measuring of
distance in 1771; it measured theparallactic anglefrom which the
distance to a point could be deduced.Dutch mathematicianWillebrord
Snellius(a.k.a. Snell) introduced the modern systematic use
oftriangulation. In 1615 he surveyed the distance
fromAlkmaartoBergen op Zoom, approximately 70 miles (110
kilometres). The survey was a chain of quadrangles containing 33
triangles in all. Snell calculated how the planar formulae could be
corrected to allow for the curvature of the earth. He also showed
how toresection, or calculate, the position of a point inside a
triangle using the angles cast between the vertices at the unknown
point. These could be measured more accurately than bearings of the
vertices, which depended on a compass. His work established the
idea of surveying a primary network of control points, and locating
subsidiary points inside the primary network later. Between 1733
and 1740,Jacques Cassiniand his sonCsarundertook the first
triangulation ofFrance. They included a re-surveying of themeridian
arc, leading to the publication in 1745 of the first map of France
constructed on rigorous principles. By this time, triangulation
methods were by then well established for local map-making,
Surveying equipment
Chain (unit)From Wikipedia, the free encyclopedia1 chain=
SI units
20.1168m2,011.68cm
US customary/Imperial units
22.0000yd66.0000ft
Achainis aunitoflength. It measures 66feet, or 22yards, or
100links,[1]or 4rods(20.1168m). There are 10 chains in afurlong,
and 80 chains in onestatute mile. Anacreis the area of 10 square
chains (that is, an area of one chain by one furlong). The chain
has been used for several centuries in Britain and in some other
countries influenced by British practice.By
extension,chainage(running distance) is the distance along a curved
or straight survey line from a fixed commencing point, as given by
anodometer.Origin[edit]The chain was commonly used with the mile to
indicate land distances and in particular in surveying land for
legal and commercial purposes. In medieval times, local measures
were commonly used, and many units were adopted that gave
manageable units; for example the distance from London to York
could be quoted in inches, but the resulting huge number would be
unmemorable. The locally used units were often inconsistent from
place to place.
In 1620, the clergymanEdmund Gunterdeveloped a method of
surveying land accurately with low technology equipment, using what
became known asGunter's chain; this was 66 feet long and from the
practice of using his chain, the word transferred to the actual
measured unit. His chain had 100links, and the link is used as a
subdivision of the chain as a unit of length.In countries
influenced by English practice, land plans prepared before about
1960 associated with the sale of land usually have lengths marked
in chains and links, and the areas of land parcels are indicated
inacres. A rectangle of land onefurlongin length and one chain in
width has an area of one acre. It is sometimes suggested that this
was a medieval parcel of land capable of being worked by one man
and supporting one family, but there is no documentary support for
this assertion, and it would in any case have predated Gunter's
work.
The main surveying instruments in use around the world are
thetheodoliteand steel band, thetotal station, thelevelandrodand
surveying GPS systems. Most instruments screw onto atripodwhen in
use. Tape measures are often used for measurement of smaller
distances. 3D scanners and various forms of aerial imagery are also
used.TheTheodoliteis an instrument for the measurement of angles.
It uses two separatecircles,protractorsoralidadesto measure angles
in the horizontal and the vertical plane. A telescope mounted on
trunnions is aligned vertically with the target object. The whole
upper section rotates for horizontal alignment. The vertical circle
measures the angle that the telescope makes against the vertical,
known as the vertical angle. The horizontal circle uses an upper
and lower plate. When beginning the survey, the surveyor points the
instrument in a known direction (bearing), and clamps the lower
plate in place. The instrument can then rotate to measure the
bearing to other objects. If no bearing is known or direct angle
measurement is wanted, the instrument can be set to zero during the
initial sight. It will then read the angle between the initial
object, the theodolite itself, and the item that the telescope
aligns with.TheGyrotheodoliteis a form of theodolite that uses a
gyroscope to orient itself in the absence of reference marks. It is
used in underground applications.Thetotal stationis a development
of the theodolite with an electronic distance measurement device
(EDM). A total station can be used for leveling when set to the
horizontal plane. Since their introduction, total stations have
shifted from optical-mechanical to fully electronic
devices.[citation needed]Modern top-of-the-line total stations no
longer need a reflector or prism to return the light pulses used
for distance measurements. They are fully robotic, and can even
e-mail point data to a remote computer and connect tosatellite
positioning systems, such asGlobal Positioning System.Real Time
KinematicGPS systems have increased the speed of surveying, but
they are still only horizontally accurate to about 20mm and
vertically to 3040mm.[8]GPS surveying differs from other GPS users
in the equipment and methods used. Static GPS uses two receivers
placed in position for a considerable length of time. The long span
of time lets the receiver compare measurements as the satellites
orbit. The changes as the satellites orbit also provide the
measurement network with well conditioned geometry. This produces
an accurate baseline that can be over 20km long. RTK surveying uses
one static antenna and one roving antenna. The static antenna
tracks changes in the satellite positions and atmospheric
conditions. The surveyor uses the roving antenna to measure the
points needed for the survey. The two antennas use a radio link
that allows the static antenna to send corrections to the roving
antenna. The roving antenna then applies those corrections to the
GPS signals it is receiving to calculate its own position. RTK
surveying covers smaller distances than static methods. This is
because divergent conditions further away from the base reduce
accuracy.Surveying instruments have characteristics that make them
suitable for certain uses. Theodolites and levels are often used by
constructors rather than surveyors in first world countries. The
constructor can perform simple survey tasks using a relatively
cheap instrument. Total stations are workhorses for many
professional surveyors because they are versatile and reliable in
all conditions. The productivity improvements from a GPS on large
scale surveys makes them popular for major infrastructure or data
gathering projects. One-person robotic-guided total stations allow
surveyors to measure without extra workers to aim the telescope or
record data. A fast but expensive way to measure large areas is
with a helicopter, using a GPS to record the location of the
helicopter and a laser scanner to measure the ground. To increase
precision, surveyors placebeaconson the ground (about 20km (12mi)
apart). This method reaches precisions between 540cm (depending on
flight height).[9]Surveyors use ancillary equipment such as tripods
and instrument stands, staves and beacons used for sighting
purposes,PPE, vegetation clearing equipment, digging implements for
finding survey markers buried over time, hammers for placements of
markers in various surfaces and structures, and portable radios for
communication over long lines of sight.Distance measurementBefore
EDM devices,distanceswere measured using a variety of means. These
included chains having links of a known length such as aGunter's
chain, or measuring tapes made ofsteelorinvar. To measure
horizontal distances, these chains or tapes were pulled taut to
reduce sagging and slack. The distance had to be adjusted for heat
expansion. Attempts to hold the measuring instrument level would
also be made. When measuring up a slope, the surveyor might have to
"break" (break chain) the measurement- use an increment less than
the total length of the chain.Perambulators, or measuring wheels,
were used to measure longer distances but not to a high level of
accuracy.Tacheometryis the science of measuring distances by
measuring the angle between two ends of an object with a known
size. It was sometimes used before to the invention of EDM where
rough ground made chain measurement impractical.Angle
measurementHistorically, horizontal angles were measured by using
acompassto provide a magnetic bearing. The deflection from the
bearing was recorded. Later, more precise scribed discs later
improved better angular resolution. Mounting telescopes
withreticlesatop the disc allowed more precise sighting.
(seetheodolite). Levels and calibrated circles allowed measurement
of vertical angles.verniersallowed measurement to a fraction of a
degree, such as with a turn-of-the-centurytransit.The Plane table
provided a graphical method of recording and measuring angles,
which reduced the amount of mathematics required.By observing the
bearing from every vertex in a figure, a surveyor can measure
around the figure. The final observation will be between the two
points first observed, except with a 180 difference. This is called
aclose. If the first and last bearings are different, this shows
the error in the survey, called theangular misclose. The surveyor
can use this information to prove that the work meets the expected
standards.
Leveling
The simplest method for measuring height is with
analtimeterusing air pressure to find height. When more precise
measurements are needed, means like precise levels (also known as
differential leveling) are used. When precise leveling, a series of
measurements between two points are taken using an instrument and a
measuring rod. Differences in height between the measurements are
added and subtracted in a series to get the net difference in
elevation between the two endpoints. With theGlobal Positioning
System(GPS), elevation can be measured with satellite receivers.
Usually GPS is somewhat less accurate than traditional precise
leveling, but may be similar over long distances.When using an
optical level, the endpoint may be out of the effective range of
the instrument. There may be obstructions or large changes of
elevation between the endpoints. In these situations, extra setups
are needed.Turningis a term used when referring to moving the level
to take an elevation shot from a different location. To "turn" the
level, one must first take a reading and record the elevation of
the point the rod is located on. While the rod is being kept in
exactly the same location, the level is moved to a new location
where the rod is still visible. A reading is taken from the new
location of the level and the height difference is used to find the
new elevation of the level gun. This is repeated until the series
of measurements is completed. The level must be horizontal to get a
valid measurement. Because of this, if the horizontal crosshair of
the instrument is lower than the base of the rod, the surveyor will
not be able to sight the rod and get a reading. The rod can usually
be raised up to 25 feet high, allowing the level to be set much
higher than the base of the rod.
Datum and coordinate systemsMany surveys do not calculate
positions on the surface of the earth, but instead measure the
relative positions of objects. However, often the surveyed items
need to be compared to outside data, such as boundary lines or
previous surveys objects. The oldest way of describing a position
is via latitude and longitude, and often a height above sea level.
As the surveying profession grew it created Cartesian coordinate
systems to simplify the mathematics for surveys over small parts of
the earth. The simplest coordinate systems assume that the earth is
flat and measure from an arbitrary point, known as a 'datum'
(singular form of data). The coordinate system allows easy
calculation of the distances and direction between objects over
small areas. Large areas distort due to the earth's curvature.
North is often defined as true north at the datum.For larger
regions, it is necessary to model the shape of the earth using an
ellipsoid or a geoid. Many countries have created coordinate-grids
customized to lessen error in their area of the earth.
The surveying profession
The basic principles of surveying have changed little over the
ages, but the tools used by surveyors have evolved. Engineering,
especiallycivil engineering, often needs surveyors.Surveyors help
determine the placement ofroads,railways,reservoirs,dams,pipeline
transports,retaining walls,bridges, or buildings. They establish
the boundaries of legal descriptions and political divisions. They
also provide advice and data forgeographical information
systems(GIS) that record land features and boundaries.Surveyors
must have a thorough knowledge ofalgebra, basiccalculus,geometry,
andtrigonometry. They must also know the laws that deal with
surveys,real property, andcontracts.Most jurisdictions recognize
three different levels of qualification:Survey
assistantsorchainmenare usually unskilled workers who help the
surveyor. They place target reflectors, find old reference marks,
and mark points on the ground. The term 'chainman' derives from
past use ofmeasuring chains. An assistant would move the far end of
the chain under the surveyor's direction.Survey techniciansoften
operate survey instruments, run surveys in the field, do survey
calculations, or draft plans. A technician usually has no legal
authority and cannot certify his work. Not all tehnicians are
qualified, but qualifications at the certificate or diploma level
are available.Licensed, registered, or chartered surveyorsusually
hold a degree or higher qualification. They are often required to
pass further exams to join a professional association or to gain
certifying status. Surveyors are responsible for planning and
management of surveys. They have to ensure that their surveys, or
surveys performed under their supervision, meet the necessary legal
standards. Manyprincipals of surveying firmshold this status.
Cadastral land surveyorsare licensed by governments. In the
United States, the federal government conducts most cadastral
surveys through the cadastral survey branch of theBureau of Land
Management(BLM).[11]They consult withForest Service,National Park
Service,Army Corps of Engineers,Bureau of Indian Affairs,Fish and
Wildlife Service,Bureau of Reclamation, and others. The BLM used to
be known as theGeneral Land Office(GLO).In states organized per
thePublic Land Survey System(PLSS), surveyors must carry out BLM
cadastral surveys under that system.Cadastral surveyors often have
to work around changes to the earth that obliterate or damage
boundary monuments. When this happens, they must consider evidence
that is not recorded on the title deed. This is known as extrinsic
evidence.[12]
Surveying has traditionally been defined as the science and art
of determining relative positions of points above, on, or beneath
the surface of the earth, or establishing such points. In a more
general sense, however, surveying can be regarded as that
discipline which encompasses all methods of gathering and
processing information about the physical earth and environment,.
Conventional ground systems are now supplemented by aerial and
satellite surveying methods, which evolved through the defense and
space programs.In general, the work of a surveyor can be divided
into five parts:1. Research analysis and decision making. Selecting
the survey method, equipment, most likely corner locations, and so
on.2. Field work or data acquisition. Making measurements and
recording data in the field.3. Computing or data processing.
Performing calculations based on the recorded data to determine
locations, areas, volumes, and so on.4. Mapping or data
representation. Plotting measurements or computed values to produce
a map, plat, or chart, or portraying the data in numerical or
computer format.5. Stakeout. Setting monuments and stakes to
delineate boundaries or guide construction operations.Surveying is
one of the oldest and most important arts practiced by bman because
from the earliest times it has been necessary to mark boundaries
and divide land. Surveying has now become indispensable to our
modern way of life.Surveying continues to play an extremely
important role in many branches of engineering. For example,
surveys are required to plan, construct, and maintain highways,
railroads, buildings, bridges, tunnels, canals, land subdivisions,
seweage systems, pipelines, etc. All engineers must know the limits
of accuracy possible in construction.
Leveling
CHAPTER 2 ROAD SURVEYING Section I. RECONNAISSANCE SURVEY
PREPARATION AND SCOPE The reconnaissance survey is an extensive
study of an entire area that might be used for a road or airfield.
Its purpose is to eliminate those routes or sites which are
impractical or unfeasible and to identify the more promising routes
or sites. Existing maps and aerial photographs may be of great
help. Contour maps show the terrain features and the relief of an
area. Aerial photographs show up-to-date planimetric details. The
reconnaissance survey must include all possible routes and sites.
The reconnaissance survey report should summarize all the collected
information, including a description of each route or site, a
conclusion on the economy of its use, and, where possible,
appropriate maps and aerial photographs. Design Design and military
characteristics should be considered during the reconnaissance
survey. Keep in mind that future operations may require an expanded
road net.
A study of the route plans and specifications is necessary. If
these are unavailable, use the following as guides. Locate portions
of the new road along or over existing roads, railroads, or trails,
whenever possible. Locate the road on high-bearing-strength soil
that is stable and easily drained, avoiding swamps, marshes, and
organic soil. Locate the road along ridges and streamlines, keeping
drainage structures to a minimum. Keep the grade well above the
high waterline when following a stream. Select a route as near to
sources of material as practical, and locate the road along contour
lines to avoid unnecessary earth work. Locate the road on the sunny
side of hills and canyons, and on that side of the canyon wall
where the inclination of the strata tends to support the road
rather than cause the road to slide into the canyon. Locate roads
in forward combat zones so that they are concealed and protected
from enemy fire. This may at times conflict with engineering
considerations. Select locations which conserve engineer assets,
avoiding rockwork and excessive clearing. Level Party The level
party establishes benchmarks and determines the elevation of
selected points along the route to provide control for future
surveys, such as the preparation of a topographic map or profile
and cross-section leveling. The level party takes rod readings and
records elevations to the nearest 0.01 foot or 0.001 meter. It sets
the benchmarks in a place well out of the area of construction and
marks them in such a way that they will remain in place throughout
the whole project. If there is no established vertical control
point available, establish an arbitrary elevation that may be tied
to a vertical control point later. An assigned value for an
arbitrary elevation must be large enough to avoid negative
elevations at any point on the project. Topographic Party The
topographic party secures enough relief and planimetric detail
within the prescribed area to locate any obstacles and allow
preparation of rough profiles and cross sections.
Survey & leveling
53 | Page
CenterLHSRHS
100.19599.785100.42
99.97100.2999.97
100.7599.8999.885
100.8599.995100.045
99.97100.59100.29
101.255100.62100.68
100.799.8299.82
100.7599.07100.77
100.0699.97100.21
100.8199.78100.34
100.57100.0199.85
100.7599.91100.76
100.67100.05100.38
100.73100.225100.02
100.75100.41100.41
100.695100.07100.07
98.3398.77598.33
98.8298.71598.01
98.7998.3698.31
98.77598.7598.33
98.78598.1298.315
98.76598.29598.42
97.04597.36597.045
97.9396.96597.705
98.13996.0696.36
98.0196.5796.53
98.0197.0196.815
98.0496.9996.74
98.0296.8496.87
98.2296.12598.22
94.393.2492.865
94.3593.2792.92
94.4192.9693.065
94.4793.47593.31
94.49593.7693.27
89.9189.9190.07
91.0790.28590.915
91.08590.0790.155
91.190.07590.18
91.1989.82589.78
91.2690.5990.14
91.2990.1690.16
90.69590.0289.56
90.80590.2190.09
90.9190.23589.78
91.0490.21890.95
91.1989.4490.05
91.33590.3290.825
91.6190.8691.11
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90.5489.2190.08
90.6288.5288.64
90.7288.6188.72
90.82590.19589.81
90.19589.1690.87
90.9789.16
91.0189.695
91.2389.65
91.39589.765
91.62
89.75
91.7690.89
91.7791.0390.685
91.3590.84
91.6190.08
91.4591.0391.75
91.31590.7690.82
91.0290.5990.48
91.1490.5190.235
91.09590.5190.11
89.82
Preliminary work in road construction is surveying &
leveling works. This consists of Traverse Survey, TBM Survey, and
Centre Line Setting out, Centre Line marking, Cross Section Survey
and Submittal of Drawings.
Traverse SurveyTRAVERSE SURVEYING
Traverse Surveying is a popular method of surveying. This
article includes definition of traverse surveying along with its
classification,errors in traversing, checks, the completed method
of traversing and plotting of traverse survey.DEFINITION
Traversing is that type of survey in which a number of connected
survey lines form the framework and the directions and lengths of
the survey lines are measured with the help of an angle measuring
instrument and a tape or chain respectively.
At the commencement of contract all the basic traverse points
will be checked and if any are found to be missing or appear to
have been disturbed, necessary arrangements should be made to
re-establish the points and traverse survey is carried out after
that.TBM TraversTBM traverse is done to establish the reduce levels
of each and every TBM with reference to the Permanent bench marks
established by us. Engineering level is used to establish
TBMs.Centre Line MarkingCenterline marking is the primary survey
part in road construction. Centerline is useful while setting out
for any road construction work. So it is very essential marking
centre line first, before any construction work.Equipment using for
centre line marking Linen tape Road marking paint Nylon cord
concrete nailsSafety equipment (e.g. Traffic cones, Bastinade
boards etc.)Centre Line Setting Out And Marking
Using total stations and approved coordinates of control points,
the road centre line should be marked at every 10m interval on the
road. With the aid of rope and road marking paint, the centre
points marked in every 10m intervals of the road should be extended
as a centre line and that established centerline should be
maintained until the end of the project.
Chain age MarkingChain age marking is done to describe the
location of the road. Chain age should be marked on the road centre
line in each 20m and 100m interval with meter and kilometer
interval respectively.Equipment used for chain age marking Linen
tape Road marking paint Nylon cord Concrete nails Ranging rods
Compass TheodoliteSafety equipment (e.g. Traffic cones, Barricade
boards etc.)Process of chain age marking Lay the nylon cord through
the 10m interval centre points and draw the centerline using chalk.
Write the chain ages using road paint.
Designed Data Of Traverse Survey
SIEVE ANALYSIS
Sieve analysis helps to determine the particle size distribution
of the coarse and fine aggregates.This is done by sieving the
aggregates as per IS: 2386 (Part I) 1963. In this we use different
sieves as standardized by the IS code and then pass aggregates
through them and thus collect different sized particles left over
different sieves.The apparatus used are i) A set of IS Sieves of
sizes 80mm, 63mm, 50mm, 40mm,31.5mm, 25mm, 20mm, 16mm, 12.5mm,
10mm, 6.3mm,4.75mm, 3.35mm, 2.36mm, 1.18mm, 600m, 300m, 150m and
75m.ii) Balance or scale with an accuracy to measure 0.1 percent of
the weight of the test sample.The weight of sample available should
not be less than the weight given below:-
The sample for sieving should be prepared from the larger sample
either by quartering or by means of a sample divider.Procedure to
determine particle size distribution of Aggregates.i) The test
sample is dried to a constant weight at a temperature of 110 + 5oC
and weighed.ii) The sample is sieved by using a set of IS
Sieves.iii) On completion of sieving, the material on each sieve is
weighed.iv) Cumulative weight passing through each sieve is
calculated as a percentage of the total sample weight.v) Fineness
modulus is obtained by adding cumulative percentage of aggregates
retained on each sieve and dividing the sum by 100.Reporting of
Results
The results should be calculated and reported as:i) the
cumulative percentage by weight of the total sampleii) the
percentage by weight of the total sample passing through one sieve
and retained on the next smaller sieve, to the nearest 0.1 percent.
The results of the sieve analysis may be recorded graphically on a
semi-log graph with particle size as abscissa (log scale) and the
percentage smaller than the specified diameter as ordinate.
WBM (Water Bound Macadam)MacadamFrom Wikipedia, the free
encyclopediaFor the Scottish family name, seeMcAdam
(disambiguation). For the regions of imperceptible colour
differences, seeMacAdam ellipse.
Macadam country roadMacadamis a type ofroad
constructionpioneered by Scottish engineerJohn Loudon McAdamaround
1820. The method simplified what had been considered state of the
art at that point. Single-sizedaggregatelayers of small stones,
with a coating of binder as a cementing agent, are mixed in an
open-structured roadway. 1Predecessors 1.1Pierre-Marie-Jrme
Trsaguet 1.2Thomas Telford 2Advent of the macadam 2.1John McAdam
2.2McAdam's methods 2.3The first macadam in North America
2.4McAdam's influence 3Water-bound macadam 4Tar-bound macadam 5See
also 6References 7Further reading 8External links
Predecessors[edit]Water-bound macadamMcAdam's road building
technology was applied to roads by otherengineers. One of these
engineers was Richard Edgeworth, who filled the gaps between the
surface stones with a mixture of stone dust and water, providing a
smoother surface for the increased traffic using the roads.[18]This
basic method of construction is sometimes known aswater-bound
macadam. Although this method required a great deal of manual
labour, it resulted in a strong and free-draining pavement. Roads
constructed in this manner were described as "macadamized."[18]
Construction of WBM roads
(I) - WBM (Water Bound macadam) roads construction:
The water bound macadam road construction technique was given by
the John Macadam. This technique in present day is used as given
below.For WBM construction we use three materials:1. Aggregates2.
Screeners3. Binders.Aggregates:We use the aggregates of different
grades. IRC(Indian Roads Congress) has classified the coarse
aggregates into 9 grades, according to their size.
For the construction of the WBM roads aggregates are used in the
sub-base, base and surface course and so the aggregates are divided
into 3 grades according to their size.Grade 1 - particles of size
90 mm to 40 mm.Grade 2 - particles of size 63 to 40 mm.Grade 3 -
particles of size 50 to 20 mm.The grade 1 aggregates having size of
90 mm to 40 mm are preferred for the sub-base material and grade 2
for the base and grade 1 for the surface course. However, if we
only use the WBM as the surface course, it gets deteriorated fast
due to abrasion with the traffic so, bituminous surfacing over the
WBM is general practice.Screenersare the aggregates of the smaller
sizes, generally 12.5 mm or 10 mm, for grade A and grade B. They
are of the same chemical composition as of the coarse aggregates.
For economic considerations IRC has suggested non plastic materials
such as, crushed over burnt bricks, moorum, gravels, etc. provided
the liquid limit of the material is less than 20%, plasticity index
is less than 6.0% and the portion of fines passing 0.075 mm sieve
is less than 10%. However if crush-able type of aggregates are
used, use of the screeners may be disposed off.
Binders: Binders, are the layers of materials which are laid
after the compaction of the aggregates and the screening materials
one after the another. Kankar dust or lime stone dust may be
utilized if locally available. The binding material with plasticity
index value of 4% to 9% is used in surface course construction; the
plasticity index of binding course material should be less than 6%
in the case of the WBM layers used as base course or sub-base
course, with bituminous surfacing. However if the screening used
are of crushable material like moorum or soft gravel, there is no
need to apply binding material, unless the plasticity index value
is low. (II) - WMM(Wet mix macadam)road construction:Aggregates
used are of the smaller sizes, varies between the 4.75 mm to 20 mm
sizes and the binders(stone dust or quarry dust having
PI(Plasticity Index) not less than 6%) are premixed in a batching
plant or in a mixing machine. Then they are brought to the site for
overlaying and compaction.
The PI(plasticity Index) of the binding material is kept low
because it should be a sound and non plastic material. If the
plasticity index is more then there are the chances of the swelling
and more water retention properties. So this value should be kept
in mind.
WBM ROAD CONSTRUCTION WBM Stands for Water Bound Macadam which
is the most commonly used road construction procedure for over more
than 190 years.Pioneered by Scottish Engineer John Loudon McAdam
around 1820 Macadam is a type of Road Construction. The broken
stones of base and surface course,if any are bound by the stone
dust is presence of moisture is called WBM Roads.Macadam means the
pavement base course made of crushed or broken aggregate
mechanically interlocked by rolling and the voids filled with
screening and binding material with the assistance of water.WBM may
be used as a sub-base,base or a surface course.The thickness of
each compacted layer of WBM ranges from 10cm to 7.5cm depending on
size and the gradation ofaggregateused.
Construction Procedure:1.Prepare the foundation for receiving
the WBM course.2.Lateral confinement may be done by compacting the
shoulder to advance,to a thickness equal to that of the compacted
WBM layer and by trimming the inner side vertically.3.Spreading
ofCoarse Aggregate.
4.Compaction ofcoarse aggregateis done by wheeled power roller
of capacity 6 to 10 tonnes or alternately by an equivalent
vibratory roller.
5.Dry screening is applied gradually over the surface to fill
the interstices in these.6.The surface is sprinkled with
water,swept and rolled.7.Binding material is applied at a uniform
and slow rate at two and more layers.8.WBM Coarse is allowed to set
overnight.
VERTICAL CURVE DESIGN
Parabolic Formulation
A Road Through Hilly Terrain with Vertical Curves in New
Hampshire
A Typical Crest Vertical Curve (Profile View)Two types of
vertical curves exist: (1) Sag Curves and (2) Crest Curves. Sag
curves are used where the change in grade is positive, such as
valleys, while crest curves are used when the change in grade is
negative, such as hills. Both types of curves have three defined
points: PVC (Point of Vertical Curve), PVI (Point of Vertical
Intersection), and PVT (Point of Vertical Tangency). PVC is the
start point of the curve while the PVT is the end point. The
elevation at either of these points can be computed asandfor PVC
and PVT respectively. The roadway grade that approaches the PVC is
defined asand the roadway grade that leaves the PVT is defined as.
These grades are generally described as being in units of (m/m) or
(ft/ft), depending on unit type chosen.Both types of curves are in
parabolic form. Parabolic functions have been found suitable for
this case because they provide a constant rate of change of slope
and imply equal curve tangents, which will be discussed shortly.
The general form of the parabolic equation is defined below,
whereis the elevation for the parabola.
At x = 0, which refers to the position along the curve that
corresponds to the PVC, the elevation equals the elevation of the
PVC. Thus, the value ofequals. Similarly, the slope of the curve at
x = 0 equals the incoming slope at the PVC, or. Thus, the value
ofequals. When looking at the second derivative, which equals the
rate of slope change, a value forcan be determined.
Thus, the parabolic formula for a vertical curve can be
illustrated.
Where: : elevation of the PVC : Initial Roadway Grade (m/m) :
Final Roadway Grade (m/m) : Length of Curve (m)Most vertical curves
are designed to be Equal Tangent Curves. For an Equal Tangent
Curve, the horizontal length between the PVC and PVI equals the
horizontal length between the PVI and the PVT. These curves are
generally easier to design.OffsetSome additional properties of
vertical curves exist. Offsets, which are vertical distances from
the initial tangent to the curve, play a significant role in
vertical curve design. The formula for determining offset is listed
below.
Where: : The absolute difference betweenand, multiplied by 100
to translate to a percentage : Curve Length : Horizontal distance
from PVC along curveStopping Sight DistanceSight distance is
dependent on the type of curve used and the design speed. For crest
curves, sight distance is limited by the curve itself, as the curve
is the obstruction. For sag curves, sight distance is generally
only limited by headlight range. AASHTO has several tables for sag
and crest curves that recommend rates of curvature,, given a design
speed or stopping sight distance. These rates of curvature can then
be multiplied by the absolute slope change percentage,to find the
recommended curve length,.
Without the aid of tables, curve length can still be calculated.
Formulas have been derived to determine the minimum curve length
for required sight distance for an equal tangent curve, depending
on whether the curve is a sag or a crest. Sight distance can be
computed from formulas in other sections (SeeSight Distance).Crest
Vertical CurvesThe correct equation is dependent on the design
speed. If the sight distance is found to be less than the curve
length, the first formula below is used, whereas the second is used
for sight distances that are greater than the curve length.
Generally, this requires computation of both to see which is true
if curve length cannot be estimated beforehand.
Where: : Minimum Curve Length (m) : The absolute difference
betweenand, multiplied by 100 to translate to a percentage : Sight
Distance (m) : Height of driver's eye above roadway surface (m) :
Height of objective above roadway surface (m)Sag Vertical
CurvesJust like with crest curves, the correct equation is
dependent on the design speed. If the sight distance is found to be
less than the curve length, the first formula below is used,
whereas the second is used for sight distances that are greater
than the curve length. Generally, this requires computation of both
to see which is true if curve length cannot be estimated
beforehand.
Where: : The absolute difference betweenand, multiplied by 100
to translate to a percentage : Sight Distance (m) : Height of
headlight (m) : Inclined angle of headlight beam, in degrees
To find the position of the low point on a SAG vertical curve: x
is the horizontal distance between the PVC and Low Point
: Grade Down (%) : Grade Up (%) : Length of Vertical Curve
(station) ei. 600 ft =6Passing Sight DistanceIn addition to
stopping sight distance, there may be instances where passing may
be allowed on vertical curves. For sag curves, this is not an
issue, as even at night, a vehicle in the opposing can be seen from
quite a distance (with the aid of the vehicle's headlights). For
crest curves, however, it is still necessary to take into account.
Like with the stopping sight distance, two formulas are available
to answer the minimum length question, depending on whether the
passing sight distance is greater than or less than the curve
length. These formulas use units that are in metric.
Where: : The absolute difference betweenand, multiplied by 100
to translate to a percentage : Passing Sight Distance (m) : Minimum
curve length (m)
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