Classification of Surveys
Different Types of Survey's in Civil Engineering
Surveys are often classified into two classes depending upon whether the spherical shape of the world is taken under consideration or not. In survey work requiring very high precision, as in triangulation for setting control stations, the curve of the earth’s surface is taken under consideration . it's then referred to as geodetic surveying. Survey conducted neglecting the curve of the earth’s surface is understood as plane surveying.
Plane Survey
In plane surveying, the curved nature of the earth’s surface is neglected. A line on the earth’s surface is taken to be a line . When three points lying on the surface of the world are joined, they form a plane triangle. Consequently, all plumb lines are assumed to be parallel. The methods of plane surveying are used when the extent of the survey is little and high precision isn't required. This assumption is justified within the case of surveys of small areas. this is often so because the difference between an arc of length 25 km and therefore the corresponding chord is merely 10mm. Further, the sum of the angles of a spherical polygon about 195 km2 in area exceeds 180° (spherical excess) by just i”. Surveys conducted for engineering projects fall into this category.
Geodetic Survey
Geodetic survey is survey finished works requiring high precision, as in triangulation surveys to determine control points and in surveys of huge areas. The equipment used for geodetic surveying are of very high precision and therefore the methods used also ensure a high degree of accuracy within the measurements. The curvature of the world is accounted for within the measurements taken during such surveys. Surveys are often further classified into categories counting on the aim , instruments, techniques used, etc
.
Instrument-based Surveys
linear times. few surveying instruments Vt ere in use, and surxevs “ere classified based upon the instruments used. Chaiiis. compasses, plane tables, and-theodolites were the sole instruments used. either alone or in connection With each other . more instruments are available now.
Chain survey
Chain survey is completed employing a chain or tape only. a sequence or tape measures linear distances. The chain triangulation of alittle area is completed by leIdlltg the world to be surveyed into variety of triangles. Using the edges of the triangles. other details are figured out . Chains and tapes meant for survey work are available in lengths of 20 or 30 m. If the length of the road to be measured is quite that of the chain length, then intemediate points need to be found out by ranging. For locating details, perpendiculars to a sequence line are often set by many methods.
Compass Survey
A compass works on the principle that a freely suspended magnet points within the magnetic north-south direction. this provides a reference direction, which remains parallel in the least stations if the world is free from magnetic influences. A compass, along side a sequence or tape, are often wont to survey a given area by many methods like triangulation or traversing.
Plane Table Survey
Plane table survey essentially combines fieldwork and plotting work. A surveying instrument may be a drafting board with modifications for attaching it to a tripod. With an alidade providing the direction, and with a sequence or tape, points are often plotted on a sheet. an idea are often prepared or, with stations already marked on the table, further details are often filled in.
Theodolite survey
A theodolite measures horizontal and vertical angles. it's a telescope which provides the road of sight and graduated horizontal and vertical circles, both with Vernier’s. Vernier theodolites with a least count of 20” are commonly used for ordinary work. Precision theodolites are made from larger diameter circles. Optic and electronic theodolites have greater precision and are easy to work . The theodolite may be a very versatile instrument and is employed for all kinds of survey work, from triangulation to traversing and filling in details.
Levelling
A level features a telescope for providing the road of sight and a supporting system for ensuring that the road of sight remains horizontal altogether directions. A graduated rod, referred to as the levelling staff, is employed with A level to seek out the difference in elevation between points.
Tachometry
A tachometer is extremely almost like a theodolite but features a stadia diaphragm having three cross hairs, The reading taken by a stadia rod or levelling staff against all the three cross hairs enables the horizontal and vertical distances to be calculated.
EDM Survey
Electromagnetic distance measurement involves the generation, transmission, and reception from a reflector at a station of sunshine , radio, or microwave signals. The phase difference between the transmitted and received signals enables the space between the instrument station and therefore the reflector station to be calculated and displayed or stored.
Total station survey
A total station may be a combination of an electronic theodolite and an EDM. Horizontal distances and horizontal and vertical angles are determined employing a total station. Total stations are utilized in triangulation surveys and other sorts of surveys needing a really high level of precision. a complete station can display and store the values required also as transfer the info to a computer for further processing.
Satellite-based instrument survey
The instruments and methods of remote sensing are often used for surveys conducted for various purposes. Global positioning systems, on the opposite hand, use an array of satellites strategically placed round the globe. Handheld trans-receivers or total stations with GPS capability receive signals from a minimum of 4 satellites and may determine the position of the receiver very accurately.
Depending upon atmospheric conditions and therefore the terrain, such instruments are often used for surveys.
Method-based Surveys
There are different methods of surveying depending upon the instruments available, the terrain, and therefore the purpose of the survey. the subsequent are common methods. ‘
Triangulation
Triangulation may be a basic method of surveying. A triangle may be a stable figure, and measuring one among the edges , referred to as the bottom line, and therefore the three angles establishes a triangle on the bottom . the opposite sides are often calculated using several formula. lf the three sides are measured; the tactic is understood as trilateration. Triangulum are often extended by adding two more sides whenever to make another triangle, thus increasing the world covered.
Traversing
A traverse are often open or closed. the edges and their directions are measured with a compass and chain or a theodolite and tape. A traverse can enclose an outsized area and therefore the details along the edges or within it are often measured from the edges . An open traverse is line narrow stretches of land like river banks, roads, of railway lines. A closed traverse may be a closed polygon-shaped figure and is run to surround an outsized tract of land. Levelling: Levelling may be a method of surveying used for determining the elevations of points. A level is employed {ET this sort of survey. When, along side the elevations, the horizontal locations of points also are determined, 5 method is understood as contouring.
Tachometry
Tachometry may be a method of surveying wherein horizontal distances and differences in elevation between survey stations are determined Without directly measuring the distances. Tachometry uses the principle of stadia Surveying. The stadia diaphragm has three cross hairs and therefore the readings taken on a staff against all the three hairs enables the calculation of distances and elevations.
Trigonometrical levelling
In trigonometrical levelling, distances and elevations are determined by measuring vertical angles to graduations on staves using the principles of trigonometry. Elevations in many cases can't be determined by ordinary levelling due to the good differences in elevation. Trigonometrical levelling provides an answer in such cases.
Purpose-based Surveys
Based upon their purpose. surveys are often classified into the subsequent types.
Reconnaissance
Reconnaissance operations are conducted to urge a thought about the terrain and any special or difficult features which will be encountered during a daily survey. Generally, no instruments are used. Distances could also be roughly estimated by pacing. Sufficient notes and sketches are drawn for future use during such surveys.
Preliminary surveys
A preliminary survey is more detailed in its scope. It locates all the prominent features of a terrain also as any particular features to be represented on a map.
Engineering surveys
Engineering surveys are very detailed surveys required to locate engineering projects like roads, railways, factories, and dams. More precise instruments and methods are used for such surveys.
Geographical surveys
Geographical surveys are conducted to gather data for the preparation of geographical maps. These maps could also be prepared to serve different purposes like specifying national boundaries, land use, contours, and resources.
Mine surveys
Mine surveys include both surface and underground surveys. Special techniques are required to transfer surface data to underground points. The surface maps show the overall layout of the mine. Subsequently, underground maps are prepared for the planning of tunnels and shafts within the mine, underground plans. geological maps, etc.
Route surveys
Route surveys are surveys conducted for locating road or railway networks. the foremost convenient alignment of roads is set supported such Surveys. Other engineering aspects like road profile, earth add cutting and banking, and road curves and super elevation are taken care of subsequently.
Location surveys
Location survey are conducted to locate points on the bottom supported the plans prepared.
Geological surveys
Geological surveys are of economic importance, as both surface and sub-surface survey are conducted to locate ores and mineral deposit. additionally , geological features of the terrain like folds and faults are located.
Defense surveys
Such surveys are conducted by the military establishment to locate strategic positions in enemy area. Aerial surveys are conducted for this purpose. Knowledge of the terrain features from ground surveys also are important to organize strategic plans for defense and attack.
Archaeological surveys
Archaeological surveys are conducted to locate relics of antiquity, civilizations etc.
Place based Surveys
Based upon the place of survey. the subsequent sorts of surveys are often identified.
Land Survey
Land surveys are done ashore to organize plans and maps of a given area. Such surveys are conducted for the aim of partitioning land, determine their areas, locate boundaries of properties, etc. Topographical surveys are surveys conducted to organize plans or maps indicating the situation of important features like buildings, rivers, and woods, including the elevation of points from some datum. Cadastral surveys or public land surveys are conducted for the aim of locating land features like agricultural fields, buildings, houses, and other property lines. Both urban and rural areas are surveyed extensively to get such data. City surveys are similar surveys conducted in cities for similar purposes but with great refinement, because the cost of the land is extremely excessive and therefore the exact location and demarcation of features become important.
Hydrographic survey
A hydrographic survey deals with water bodies like lakes, rivers, streams, and coastal areas. the target is to get data to style water navigation systems, determine shorelines, help within the design of structures inbuilt water or along shore lines, and acquire data about the bottom surface underneath water.
Aerial survey
An aerial survey is completed from aircraft, which take photographs of the surface of the world in overlapping strips of land. Extensive areas are often covered by such surveys. this type of survey is additionally referred to as a photogrammetric survey. the tactic is extremely expensive. It is, however, recommended in large projects in difficult terrain where ground surveys could also be difficult or impossible.
Underground survey
Underground surveys are wiped out the case of mines and tunnels. These are done by transferring ground points to the underground level and conducting surveys of tunnels, caves, mines, etc.
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