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IntroductionAccurate and complete subsurface information is necessary for all types of civil engineering projects, for without this information it is not possible to arrive at a rational design for structure and proper construction procedures. Structures have failed because of inadequate or misleading subsurface data, and many so called successful structures could probably have been completed at much less cost because proper consideration have been given to obtaining more complete subsurface information. Boring and Sampling MethodsAuguring is a simple method of putting down holes a few inches in diameter to depths up to 20ft in soft sediments. Trial pits and trenches in addition to providing samples of the deposits excavated, allow inspection of the rocks in the walls and floor over an area. Boreholes allow much greater depths to be penetrated. Boring methods are broadly of two kinds: 1. Percussion DrillingIn percussion drilling the bit is suspended from the rods (or a cable) and is jumped up and down so that the rock is broken up by repeated rows. Water is added to the hole to keep the bit cool and make slurry and debris removed by means of a bailer. The pounded rock mixed with water from slurry, from which chips may be recovered for identification. The rate of progress of drilling, and the cost varies according to the hardness encountered. 2. Rotary DrillingRotary drilling methods include mud rotary drilling and core drilling. In the former the bit is rotated, and is attached to hollow drilling rods through which a fluid mud is pumped continuously. The mud is returned to the surface through the annular space between the rods and the hole, bringing with it small fragments of rock which can be screened out and examined. The rods are usually in 20 ft lengths, and successively added to the assembly as the hole is lowered. 3. Core DrillingCore drilling uses a tabular bit with a lower cutting edge, which is rotated in the hole; many forms of bits are available, some containing diamonds and other hard abrasives for penetrating hard rocks. Diamond drills with a diameter of 2 to 4 inches are commonly used, for sampling, or in exploratory bore from underground workings and holes can be drilled at any angle. As the bit is rotated, a core is cut out and enters a barrel mounted above the bit. The length of the barrel controls the length of the core which can be obtained at any time. The core is recovered by drawing the drilling rod and barrel. The cost of core drilling is greater than for any other method and increase greatly with increasing depth of the hole; but the recovery of the core is a great advantage, as it yields information from great depth and is a sample of rocks drilled through. 4. Core BarrelsThe aim of structural drilling is to recover undisturbed core upon which measurements of structural features can be made. This can be achieved either by the multiple-tube core barrels or by the use of large diameter barrels. In the multiple-tube core barrel, the inner tube or tubes are mounted on a bearing so that they remain stationary, while the outer barrel, which carries the diamond bit, rotates. The core, cut out by bit, is transferred into the non-rotating inner barrel where it remains undisturbed until the barrel is removed from the hole. Removing the core from the barrel is the most critical part of the operation. The most satisfactory system is to use a split inner barrel which is removed from the assembly with the core inside it and then split to reveal undisturbed core. 5. Geophysical MethodsGeophysical methods allow subsurface features to be located, mapped, and characterized by making measurements at the surface that respond to a physical, electrical or chemical property. These non-invasive measurements can be effectively used to provide reconnaissance to detailed geological information guide, subsurface sampling and excavation, and provide continuous monitoring. If all sites were simple (horizontally stratified geology with uniform properties), site characterization would be easy. Data from just one boring would be sufficient to characterize the site. However in most situations, this will not be the case. Even at sites where geology appears to be uniform, one must be alert to often-subtle variations that can cause significant changes in structural or hydrological properties. Traditional approaches to subsurface field investigations commonly rely only on the use of direct sampling methods such as boring of rock and soil samples, monitoring wells for gathering hydro geologic data points. Soil and rock sample programs and the placement of boring and wells are done mainly by educated guess work. Numerous pitfalls are associated with this approach that can result in an incomplete or even erroneous understanding of site conditions. These oversights are the cause of many structural and environmental failures. In many cases direct sampling alone is not sufficient to accurately characterize site conditions. This is the primary reason for the application of surface geophysical methods. Surface geophysical measurements can be made relatively quickly; they provide means to significantly increase data density. Because of the greater sample density, anomalous conditions are more likely to be detected, resulting in an accurate characterization of subsurface conditions. 5.1. ApplicationThere are four major areas where surface geophysical methods may be applied to environmental and engineering problems: 1) Assessment of natural geologic and hydro geologic conditions. 2) Detection and mapping of contaminant plumes, spills and leaks. 3) Detection and mapping of landfills, trenches or other underground structures and utilities. 4) Evaluation of soil and rock properties and man-made structures. The following is a summary of various geophysical methods: 6. Seismic MethodsSeismic measurements involve the measurement of seismic waves travelling through the subsurface. Stratigraphy, structure, and material properties can be assessed with seismic methods. All applications of seismic methods are based on the fact that the elastic properties of soils and rocks determine the velocities of wave propagation through them. The higher the elastic modulus, for example, higher the velocity is. In rocks the dominant factors that influence the velocity are the crystallinity and porosity. Rocks having crystalline textures and low porosity have higher shock wave velocities just as they have high elastic moduli and compressive strengths. Shock waves in earth materials follow multiple paths from source to receiver. In the near surface, waves take a direct path from source to receiver and the measurements of elapsed travel time for measured distance results in the wave velocity through that material. Waves moving downward into the earth may be refracted and reflected at velocity interfaces. The ray-path diagram is a convenient method of showing wave propagation by direct, refracted and reflected paths. Unless otherwise noted, all velocities refer to compressional waves. Seismic data are obtained by recording shock-wave travel time between a source and a receiver, or geophone, for various chosen distances. Two general types of seismographs are used in engineering applications. One type permits the simultaneous, multichannel recording of shock-wave arrivals at a number of geophone locations from a single energy source such as a buried explosive charge or a weight-dropping system. The output from the geophones may be recorded in analog and digital forms in a variety of ways, all having a time base to permit extraction of elapsed travel times to each geophone location. Two advantages of multi-channel recording are; (1) single energy source for all geophone channels, and (2) more sophisticated filtering, recording, data processing, and printout capabilities than simpler single-channel seismographs. Disadvantages include higher firs cost, greater operating cost, large size, and often the need for greater peripheral support such as computer hardware and software. The second type of seismographs is a single-channel instrument that records shock-wave travel time from a source to a single geophone location. As a result, the operation must be repeated for different geophone distances until a suitable number of travel times have been obtained. Single-channel seismographs may record geophone output in several ways such as on an oscilloscope; on a chart, as in multichannel unit; or only as a first-arrival pulse time digitally (or by some other means). Timing systems are inherently a part of each system. Single e-channel seismographs are low initial cost, small size and provision for tailoring of geophone recording distances to the given site as work progresses. Disadvantages include time require for obtaining data, lack of single energy source for the entire geophone spread, and usually a restriction of use to refraction seismic surveys. 6.1. Seismic RefractionIt is a method used to determine the P-wave velocity structure of the subsurface. Seismic P-waves are generated on the surface, propagate through the soil and rock, and are recorded by geo-phones at known distances from the source. When seismic waves encounter interfaces separating materials of different seismic velocities, the waves are refracted according to Snell's Law. At the critical angle for each interface (energy refracted 90 degrees) the seismic wave will travel along the interface with velocity of underlaying layer. A seismograph is used to record the travel times of these first arrivals, after which seismic velocities can be derived. Depths to the refracting layers can also be determined. Primary applications include determination of depth to bed rock and thickness of geologic strata, rippability and dredge-ability, and in-situ elastic modulus of soil and rock. It can provide data to depth of 100 ft or more and resolves up to 2 to 3 layers. It also provides a 2D cross-section of P-wave velocity. The source of seismic energy can be as simple as 8-pound sledge hammer. Deep measurements may require explosive as an energy source.If a velocity interface is not parallel with the surface, the velocities recorded at the surface are apparent rather than true velocities. The velocities recorded or plotted will be less than or greater than true velocity when energy is travelling down-dip or up-dip, respectively. The shallower down-dip end will exhibit a lower intercept time and critical distance compared to the deeper or up-dip end. 6.2. Seismic ReflectionSeismic reflection measures the travel time of seismic waves from the surface downwards to geologic contacts where part of the seismic energy is reflected back to hydrophones at the surface. A reflection will occur from geologic strata when the reflection coefficient (derived from density and seismic velocity contrasts) between strata is sufficient. After raw data are processed, a cross-sectional picture of subsurface strata and anomalous conditions can be developed. Primary application is for determination of depth and thickness of geologic strata, structural and anomalous condition. The depth ranges from as shallow as 30 ft to greater than 100 ft. 6.3. Down-hole seismic surveysThese are the simplest and cheapest method as they required only a single borehole. Seismic energy is generated on surface at a fixed distance from the top of the borehole. The travel times of the first-arrival seismic waves measured at regular intervals down the hole using string of hydrophones or in case of S-wave surveys, a single clamped tri-axial geophone that is gradually moved down the hole. P and S wave arrival time for each receiver location are combined to produce travel time versus depth curves for the complete hole. These are then used to produce total velocity profiles from which interval velocities and various elastic moduli can be calculated (in conjunction with density data from geophysical logging of borehole). 6.4. Cross-hole Seismic SurveysThis involves measurement of the travel time of seismic energy transmitted between two or more boreholes in order to derive information on the elastic properties of intervening materials. One hole is used to deploy the source while the other hole(s) are used to detect the arrival of the seismic energy. The travel time of the seismic waves are derived from the first arrivals identified on the seismic trace for each short-receiver position and are used with the known distances between the short/receiver boreholes to calculate the apparent velocities (P & S) for each depth interval. This data is then used to derive a vertical profile of the various elastic moduli. The relationship between the velocity of seismic waves and the density and elastic properties of the materials through which they are travelling means that seismic techniques can be utilized to provide information on various geotechnical properties of the subsurface, such as Poisson's ration and shear modulus. The most common method of measuring these properties in engineering studies through the use of cross-hole seismic surveys. 6.5. Cross-hole Seismic TomographyBorehole seismic tomography involves the measurement of the travel times of seismic ray paths between two or more boreholes in order to derive an image of seismic velocity in the intervening ground. Data is collected using one hole for the seismic source (normally a speaker) and measuring one arrival time using strings of hydrophones in the other. Travel times are collected at regular intervals (usually 0.5 m to 2 m) all the way down the hole(s) for each short position. This results in a network of overlapping ray paths that can be used to model the velocity profile. The resulting velocity image is termed a tomogram and enables identification of anomalous velocity zones laying between the boreholes as well as imaging individual velocity layers. The primary applications of borehole seismic tomography is in engineering studies for the identification of features such as fault zones and voids when combined with S-wave survey, the data can additionally be used to provide information in material stiffness properties. 7. Electrical ResistivityElectrical resistivity measurements are made by placing four electrodes in contact with soil or rock. A current is caused to flow in the earth between on pair of electrodes while the voltage across the other pair of electrodes is measured. The depth measurement is related to the electrode spacing. The resistivity measurement represents the apparent resistivity averaged over a volume of the earth determined by the soil, rock, and pore fluid resistivity, along with the electrode geometry and spacing. In contrast to wave velocities in refraction seismology, resistivity values are not representative of specific physical properties of earth materials no do they remain constant over time. The flow of current through soil and rock is by ion conduction, which is dependent on a combination of the conductivity of the fluid present, porosity, and percentage of saturation. Dissolved salts in water provide for ion conductance of electrical current. The conductance that is the reciprocal of resistance is directly proportional to amount of dissolved salt in water, or salinity. The amount of fluid regardless of its salinity that can be present is controlled by the porosity of material. The more interconnected the pore spaces, the greater the ease of ion migration through the material. In addition, the degree of saturation that varies with season, in turn affects conductance (or in the context of this discussion resistivity). Seasonal fluctuations in resistivity of as much as 200% have been reported. The rock forming minerals normally are highly resistive to current flow. An exception, which complicates resistivity work, is the presence of clay minerals. The exchangeable ions in the clays may separate from the lattice and make the pore water conductive even though the formation water may not be saline. As a result, clays have low resistivity – whether occurring as clay-rich soils or as shales. If we are certain that the groundwater in an area is fresh, low resistivity is representative of clay. Conversely, freshwater (a poor conductor) will cause high resistivity when present in the poor spaces of a clean or clay-free soil or in the pores or joints of a porous or dense, relatively clay-free rock. Note, however, that there is nothing distinctive about the kind of material that has high or low resistivity values, as is the case with seismic velocities. For instance, it would be possible on the basis of high resistivity to drill expecting to encounter porous, freshwater-bearing sand and instead encounter tight sandstone. Also saline pore water in sand or porous or highly fractured rock gives low resistivity values that are also indicative of clay or shale. Because of these perplexing problems, there is the need for subsurface control of materials and thickness from either exposures or boreholes. 8. MagneticThere are two primary applications for magnetic measurements; 1) locating and mapping buried ferrous metals, and 2) mapping geologic structures. The presence of buried ferrous metals creates a local variation in the strength of the earth's magnetic field permitting the detection and mapping of buried ferrous metal. Total field measurements made with one magnetometer, and gradient measurements made with two magnetometers are commonly used. Magnetic gradient measurements are made by a gradiometer, which is simple two magnetic sensors separated by a constant offset. Magnetic measurements can be used for geologic mapping by responding to the magnetic susceptibility of soil and rock. Generally total field measurements are used for geologic mapping. The primary application is for mineral exploration and for characterizing geologic structures such as faults. 9. MicrogravityA microgravity survey provides a measure of change in subsurface density. Natural variations in subsurface density include lateral changes in soil or rock density, buried channels, large fractures, faults, dissolution-enlarged joints and cavities. A microgravity survey consists of making sensitive gravity measurements at the micro Gal (µGal) level (1/1000 of a milliGal or 10E-9 of the earth's gravitational field) with a gravimeter. Gravity measurements are acquired at discrete points along a profile line or within a grid, and are corrected for instrument drift, tidal effects, elevation changes, and latitude. Gravity anomalies are directly related to lateral variations in subsurface density. This method is used to identify caves, voids, skin-holes and weathered zones. It is also used to map top of rock. It can also be used to identify man-made structures such as tunnels and mines. 10. Ground Penetrating RadarGround penetrating radar (GPR) uses high frequency electro-magnetic waves to acquire subsurface information. Energy is radiated downward into the ground from a transmitter and is reflected back to receiving antenna. The reflected signals are recorded and produce a continuous cross-sectional profile of shallow subsurface conditions. Reflections of the radar wave occur where there is a change in the di-electric constant or electric conductivity between two materials. These changes are associated with natural hydro-geologic conditions such as bedding, cementation, moisture, clay content, voids and fractures. Large changes in dielectric properties often exist between geologic materials and man-made structures such as buried utilities or tanks. This technique is also used for the location of rebar in concrete nondestructive testing of man-made structures. Ground penetrating radar is also used to map void space behind concrete tunnel lining.

ObjectThis System provides us with accurate horizontal and vertical measurements and gives us the position of observer in terms of Latitude and Longitude. AdvantagesThis system is fast replacing with conventional methods of surveying like Triangulation, Traversing etc. It no longer requires the inter-visibility of station points. The conventional techniques are still required for detail surveying. The horizontal and vertical control can easily be established with the help of GPS. InstrumentsThis system basically requires the receiver which is setup at the point of observation. The second part of the equipment is no of satellites which are 18, launched into 6 different orbits.Each orbit have three satellites with 120 degrees interval. The height of satellite is about 20,000 km with orbiting velocity of 11hr 58min. The GPS is controlled from an airforce base in California. ProcedureThe GPS position is achieved by the precise measurement of the distance between the satellite & the receiver at an instant of time. For a three dimensional measurements three or four satellites will be needed depending upon the quality of receiving equipment. It requires highly accurate clocks both in the transmitter and in the receiver to measure the precise distance between them. ApplicationsThis system gives us the accurate geographic position required for land surveying. It is used for navigation purposes in Aircraft,Ships,Submarines etc. It is now exceedingly used to locate the enemy targets and subsequently hitting them by GPS information guided missiles. For public use simpler version are available for locating the vehicles, the individuals and the parties, in hiking and mountaineering expeditions and other number of applications.

1. IntroductionSubsidence is displacement of ground surface vertically over a broad region or at localized areas. It may be either a gradual lowering or a collapse. This can have costly effect on facilities and structures over a subsiding area. Subsidence results from a number of different mechanisms. It can occur as a consequence of natural processes. The dissolving of limestone, salt, or other soluble materials creates underground openings that may collapse. Collapse may also occur in the roofs of lava tubes in areas underlain by volcanic rock. Withdrawal of fluids from subsurface reservoirs can create human-induced subsidence. This type of subsidence has resulted from extracting oil, gas and ground-water. Underground mining is another mechanism for creating subsidence by creating subsurface openings. Natural solution of rock leading to collapse of the overlaying surface can be a rather spectacular form of subsidence. A single sinkhole 324-ft wide and 100-ft deep was formed by collapse on May 8-9, 1981, in Winter Park, Florida. It destroyed a house, several cars, streets, parts of neighboring buildings, and the city swimming pool, causing losses estimated to exceed $2 million. Groundwater withdrawal for surface uses or dewatering of quarries and mines causes a general lowering of the water table. Construction activities are a less-common cause of collapse. Subsidence because of construction can result from loading the ground surface over a cavity or from the diversion of surface water, thus changing the groundwater system and increasing sinkhole development. Subsidence caused by underground mining results in severe economic losses in some areas. It is estimated that damage amounting to $30 million annually results from subsidence over abandoned coal mines. Underground mining notably coal mining, creates subsurface openings. Rock layers bridging these voids may fracture and collapse into the opening, with resultant lowering of the ground surface. Subsidence causes differential settlement, with the greatest amount near the center of the opening. Associated with this differential settlement are ground cracks. The extent and size of cracks will change until subsidence is complete in an area. Withdrawal of oil, gas and water has produced subsidence that has resulted in extensive losses in Arizona, California, and along the gulf coast of Texas. Subsidence causes damage in several ways. The most obvious causes are in tilting, cracking, and shearing of structures where subsidence produces differential settlement. Large-scale collapse can completely destroyed some structures. Destruction results when water-containment structures such as reservoirs and canals are breached. Subsidence causes damage impairing the function of some surface facilities. It can create low points in pipelines and alter the alignment of microwave transmission stations. A more-subtle consequence of subsidence is ground lowering that makes more land subject to flooding. 2. Evaluating Subsidence ProcessesIt should be clear from our discussion that evaluation of subsidence processes depends on a variety of methods. Evaluating possible underground openings will require a very different approach than estimating subsidence from fluid withdrawal. The potential of solution-caused subsidence depends on the presence of limestone or other soluble rock type. Examining the natural subsidence occurring where these rocks are present serves as an initial indicator. For example, a sinkhole-density map compiled by means of aerial photography is useful measure of relative collapse potential. Similarly, the potential for subsidence from underground mining exists only where mining is active or was conducted in the past. Historical records or the details surface surveys normally conducted by many present day mines provide a basis for evaluating subsidence potential. The extent of subsidence depends on factors such as: 1) thickness of mined coal, 2) mine geometry and mining methods and 3) thickness, lithology, structure, and hydrology of bedrock and surficial material in the mining area. Detecting solution cavities or abandoned mine openings is mostly reliably done with the drilling. However, expense limits such drilling over large areas. Earth-resistivity surveys can detect openings at depths up to 25m. Gravity surveys are marginally successful; only large openings near the surface are detectable. Subsurface radar techniques proved too unreliable for practical use. There are two field-based techniques for subsidence prediction where fluid is being withdrawn. One is the depth porosity method, and other is aquitard-drainage method. Estimating subsidence in an area where fluid withdrawal is being initiated is best done with the depth-porosity method. For the more complicated situation in which subsidence is already active, the aquitard-drainage method is recommended. Ground failures in areas subsiding owing to fluid withdrawal can be predicted. These ground failure range from tension cracks to surface faults. Prediction of ground failure in areas where deformation is underway requires monitoring of surface conditions for sign of failure. In areas not yet subject to subsidence, prediction requires determining the particular surface conditions conducive to failure. 3. Mitigating the Effects of Subsidence ProcessesControlling land use to avoid large-scale changes in the regional water table is one way to avoid subsidence in areas underlain by soluble rock. Avoiding withdrawal overdraft from compressible groundwater aquifers is equally effective in avoiding subsidence. Reservoirs from which oil, gas, or geothermal fluids is being withdrawn can be re-injected with water to compensate for the lost fluids. In some instances, subsidence over mines need not result in structural damage. This requires knowing the specific factors that influence subsidence at that locality and conducting mining in a manner that permits a general lowering of the entire area in which a structure is situated. This minimizes the differential settlement responsible for most of the distress to structures. Structures damaged or impaired by subsidence can be restored in many cases, this involves sealing the cleaned-out sinkhole, restoring the ground surface, ensuring that surface water to site is minimized, and promoting groundwater flow down gradient from the repair location. Some problems with solution-related subsidence are human related. This is especially true where natural sinkhole is used to drainage. Diverted water can increase the groundwater gradient in areas, leading to greater subsidence. Subsidence controls over mined areas generally takes the form of either providing selective support for the structure or filling the underground space to halt further subsidence. In an effort to control subsidence affecting an electric substation in Pennsylvania, both approaches to dealing with subsidence were used. Selective support involved placing drilled piers and piling seated into rock below the base of the mined coal seam. Fly ash was injected through drill-holes to fill some underground openings. In 15 selected locations, grout columns were constructed.

What is an adjustment?Adjustment of a theodolite means the operation of tightening or loosening of moveable parts to prepare the instrument for accurate measurement. It also includes other operations meant for this purpose. There are two types of adjustments for a theodolite - Temporary Adjustment & Permanent Adjustment. 1 - Temporary adjustmentsThese are required for each setting up of the instrument and includes following, a - CenteringThis is to center the instrument exactly over the ground station which is indicated by optical plummet. b - LevelingIt means to make the horizontal and vertical axes in their true position. It is indicated by the central position of plate level. c - Removal of parallaxThat is to bring the cross hairs and the object in focus simultaneously 2 - Permanent adjustmentsThese are to be tested after a long interval or at the beginning of an important project. The field party is only expected to carry out the test and adjustment, if required will be done by the trained for this purpose in a workshop. Permanent Adjustments for a theodolite have discussed below, a - Plate level adjustmentIts purpose is that bubble should remain central in all positions after the adjustment. Its procedure is as follows, After making the circular bubble central bring the plate level parallel to any two-foot screws. Move the two-foot screws inward or outward till the bubble is central. Rotate the instrument through 90° and with the help of third foot screw bring the plate bubble in the central position. Repeat the process at least two times so that bubble is central at the end of each step. Now, rotate the instrument through 180°, if the bubble remains central then Adjustment is correct otherwise it is to be done. b - Horizontal axis adjustmentIts purpose is that the horizontal axis should be remain truly horizontal after the instrument has been carefully leveled. Its procedure is as follows, Setup and level the instrument at a position where highly inclined sight is available. Move the telescope in upward direction to bisect a well-defined elevated point. Now, depress the telescope and take a staff reading on the horizontally placed staff below the elevated point. This observation is taken with face left. Now, change the face and again bisect the same elevated point. Depress the telescope and take the staff reading, if the two reading are same then Adjustment is correct. c - Line of collimation adjustmentThe line of collimation must pass through the point of intersection of cross hairs and optical center of the object glass (also the geometric center) and line joining the intersection of cross hairs. Its procedure is as follows, Setup and level the instrument carefully at a position from where about 100 ft long sights are available on the opposite sides. Fix the horizontal movement and fix an arrow at a distance of 100 ft and bisect it by vertical hair with face left. Transit the telescope and take the staff reading on the horizontally lying staff at a distance of about 100 ft. Rotate the instrument though 180° and again bisect the arrow. Now, again transit the telescope and take the staff reading, if the two readings are the same then the Adjustment is correct.

SurveyingSurveying is a technique in by which measurements are taken on the surface of the earth and presented on the maps or stored in the digital format and vice versa. There are following types surveying, 1. Plane surveyingIt is meant for small areas where the surface of the earth is taken to be plane surface, i.e. curvature of the earth is ignored. e.g. for survey inside a city. 2. Geodetic surveyingIn this curvature of the earth is taken into consideration. e.g. National surveys, Basic triangulation network of a country. Geodesy is termed as actual shape of the earth. Surveying mapsThere are following types of surveying maps: 1. Topographic mapsIt shows natural and artificial features on the surface of the earth. Surveying done for this purpose is called topographic surveying. 2. Engineering mapsThes maps shows the detail of engineering projects, e.g. roads, bridges, dams. Surveying done for this purpose is called engineering surveying. 3. Geographic mapsThese are about the political boundaries of the country and used by general public. Surveying done of these purposes are undertaken by the state agency. e.g. in Pakistan state agency is "Survey of Pakistan" 4. Cadastral mapsThese shows ownership rights of individual or communities. Surveying done for this purpose is called cadastral surveying.

PhotogrammetryPhotogrammetry is the branch of surveying in which measurements are made from photographs. MeritsThis is a very quick and accurate method of surveying in which the ground observations are almost totally eliminated. This is very accurate method if true interpretations of photographs are made. It also provides means to develop a Contour map. DemeritsThis method requires fair weather conditions. The instrument is very expensive, and staff should be highly qualified and experienced to make full use of this method. Types of PhotogrammetryThere are Two main Types of photogrammetry - aerial photogrammetry and terrestrial photogrammetry. 1. Aerial photogrammetryIn these photographs are taken from specially manufactured plane. The characteristics of this procedure are following: The plane is made to fly along the center of longitudinal strips marked with the help of clearly visible ground monuments. The speed of aircraft being known the camera speed is adjusted accordingly to provide the requisite transverse and longitudinal overlap between successive photographs. The speed of the aircraft, its height and specification of the camera are already known. The photographs are then developed in laboratory with each photograph being placed in its proper position and by cutting the overlapped edges. This will provide a base map on the basis of actual photographs which can be processed further for particular requirements. The scale of photographs can be established by distances on the ground between two points and this dimension on the graph. The contours can be drawn by putting the photographs under the stereo plotter. Stereo plotter is an optical device which gives three-dimensional view of plane photographs. 2. Terrestrial photogrammetryIn this type, the photographs are taken from elevated ground stations. Further development of these photographs will take into account the elevations of camera and tilt of the axis of photograph. This method is very similar to previous one except that the camera is in stationary position. The camera used in this method is called photo-theodolite as it will require the same features as theodolite. This type of photogrammetry is much cheaper and can be carried out by individual surveying firms also.

By deflection angle methodBearing of the first line AB is measured with the help of prismatic compass or by any other method. Setup the theodolite and point B and with horizontal circle reading bisect point A. Transit the telescope and rotate it in the direction of next station point C and note the angle, this will be θ1 R and is called deflection angle at B. Repeat this procedure for the remaining points of traverse measuring the deflection angle and writing with them letter "L" or "R". For calculation of bearing we have to simply add the deflection angles right ® to bearing of previous line to find out the bearing of next line and subtract the deflection angle left (L) from the bearing of previous line to find out the bearing of next line. Examplelet θ1 = 35°, θ2 = 55°, θ3 = 45°, Bearing of AB = 65° 00′ 00″ Add 35° R = 35° 00′ 00″ Bearing of BC = 100° 00′ 00″ Subtract 55° L = 55° 00′ 00″ Bearing of CD = 45° 00′ 00″ By direct Bearing method Bearing of first line AB is determined by any method. Setup the instrument at point B. Set the horizontal circle reading at the Back Bearing of AB and bisect the back station A. Rotate the instrument in clockwise direction and bisect the next point C. The circle reading will give directly bearing of line BC. Repeat the procedure for remaining lines.

For open traversing Following procedure is adopted in case of open traversing with the help of prismatic compass, We will setup the compass at point A, B, C and so on and note the Fore Bearing and back Bearing of lines. The length of lines or legs are measured by chain twice and mean lengths are calculated. During taking measurements in the field, the method used angular measurement, and linear measurement should be of same standard of accuracy, i.e. either combination of Prismatic compass and Chain or combination of theodolite and metallic tape. For closed traversingIn case of closed Traversing while using Prismatic compass, the interior angles can be calculated by comparing the bearings of adjacent lines. The above rule also applied in case of closed Traverse with Theodolite. Check for closed traverse∑ Interior angles = (2N - 4) × 90°, where N is no of sides of closed traverse.

Vertical angleIt is the angle in the vertical plane between horizontal line passing through the intersection of cross hairs and inclined line joining intersection of cross hairs and the point being observed. Circle reading in case of vertical angleDuring Face left vertical angle will be computed in the following manner, When angle of elevation, vertical angle = 90° - Circle reading. When angle of depression, vertical angle = Circle reading - 90°. Now, during Face right vertical angle will be computed in th following manner, When angle of elevation, vertical angle = Circle reading - 270°. When angle of depression, vertical angle = 270° - Circle reading. Example for method of bookingAngle Face Circle reading (° ′ ″) Angle value (° ′ ″) Mean (° ′ ″) Remarks * L 69 58 30 20 01 30 20 01 45(+ve) Elevation R 290 02 00 20 02 00 In case of angle of elevation value of vertical angle will be +ve while in case of depression it will be -ve.

IntroductionSometimes it needs to approximate the distance between two points. One can do it without using any distance measuring instrument. But firstly, you need to compute your own pace length, then you can use your pace length to approximate the actual distance. However, it is not accurate enough to use into the calculations or computations. Procedureopen a chain and let it fly in straight position along the piece of ground. Walk along the chain and count the number of steps. The distance being known personal pace length will be equal to length of the chain divided by number of steps. Repeat the observation for two or three times. ExampleLength of chain No of Paces Pace Length 30m 44 0.68 30m 43 0.69 ApplicationNow, you just need to multiply the number of steps you walked between two points to your pace Average pace length. Approximate Distance = Pace length × No of steps walked Useful Conversions1 feet = 12 inch. 1 m = 3.28 feet. 1 inch = 2.5 cm. 3 inch = 0.25 feet.

1. PacingPermissible error ≤ 1 feet in 20 feet. 2. ChainPermissible error ≤ 1 in 1000. 3. Metallic tapePermissible error ≤ 1 in 1000. 4. Steel tapeThis tape is made of steel alloy of very small co-efficient of thermal expansion. Permissible error ≤ 1 in 1000. 5. Invar tapeThis tape is made of very expensive steel alloy of almost negligible co-efficient of thermal expansion and is used for very precise linear measurements. Permissible error ≤ 1 in 50,000. 6. TachometryPermissible error ≤ 1 in 50,000. 7. Electronic distance meterPermissible error ≤ 1 in 100,000.

LevelingIt is the branch of Surveying in which relative elevations of points are determined. There are following Types of Leveling 1. Ordinary levelingIt is general purpose Leveling and unless otherwise stated all types of Leveling will come into this category. 2. Reciprocal levelingThis is done when a site is unusually long, i.e. crossing the river. Sights are taken from the two banks by placing the staff on the opposite bank almost simultaneously and finding the average of apparent difference of level. This method eliminates the error due to curvature and refraction. 3. Precise levelingThis is a special type of Leveling using very precise level fitted with parallel plate micrometer and using precise staff with invar strip This is used for establishing new bench marks and therefore is undertaken by state agencies. 4. Barometric levelingThis type of leveling is used in higher surfaces of earth like mountains. Application of levelingLongitudinal Sections (L-Sections): It is done to determine the levels at given intervals along the center of level road. Cross Sections (X-Sections): These are the levels at a given cross section of a road or any engineering work Contouring Invert levels for sewers Head rooms from bridges: Staff is used in inverted position from the zero-end touching the ceiling of the bridge, the reading is entered as -ve and R.L of that position is calculated in usual manner.

1. TripodIt should be of a rigid type capable of fixing the position of the instrument with a small lateral movement on its top when required. 2. Foot screwsThese are provided for leveling the instruments. 3. Plate levelProvided for checking the level of the instrument. 4. Horizontal clampProvided to clamp the movement in horizontal plane. 5. Vertical clampFor clamping movement in vertical plane. 6. Slow motion screwsThese screws are used to move Theodolite either vertically or horizontally in small fractions. 7. TelescopeIn a telescope vertical hair is used for horizontal angle measurement while horizontal hair is used for vertical angle measurement. Focusing arrangement for the object glass is usually provided in the body of the telescope. Collimator is provided to bring the object in the field of view. 8. Vertical axisIt is the axis around which the telescope rotates in horizontal plane. 9. Horizontal axisIt is the axis around which telescope rotates in vertical plane. 10. Optical plummetIt is provided for centering the instrument over a ground station. 11. Angle reading arrangementIn screen display you can note angle measurements taken with Theodolite.

Fore bearingIt is the bearing of line when the first letter of line say AB is taken as origin. This is to be written as Fore Bearing (F.B). Back bearingIt is the bearing of line when second letter of line say AB is taken as origin and this is to be written as Back Bearing (B.B). Theoretical difference between Fore Bearing (F.B) and Back Bearing (B.B) should be 180°. Local attractionIf the difference between magnetic Fore Bearing and Back Bearing of a line is not exactly 180°, it may be due to presence of local attraction at one of both stations. If this difference is exactly 180° then both stations are free from local attraction. Local attraction may be due to following reasons. Overhead electrical wires Magnetic materials in the vicinity Practice problemIn the following table observed Bearings are given, we will compute the corrected bearings and Internal Angles. Line Observed Correction Corrected F.B B.B F.B B.B AB 70° 00′ 251° 00′ A= +30′ , B= -30′ 70° 30′ 250° 30′ BC 328° 00′ 145° 00′ - 327° 30′ 147° 00′ CD 225° 00′ 71° 00′ - 257° 30′ 77° 30′ DA 139° 00′ 316° 00′ - 136° 30′ 316° 30′ By observing the table, it may be noted that no line has a difference of exactly 180° between Fore Bearing and Back Bearing. In such a case, a line where the difference is closest to 180° is selected. Such a line is called line of least disagreement, for this line correction is assign to each of the two stations of that line with opposite sign. In the above table line AB is selected for error distribution. Now, we will compute internal angles from these corrected Bearings. A = (360° - 316° 30′) + 70° 30′ = 114° 00′ B = 327° 30′ - 250° 30′ = 77° 00′ C = 257° 30′ - 147° 30′ = 110° 00′ D = 136° 30′ - 77° 30′ = 59° 00′ Before computation of internal angles, you need to draw a rough sketch of scheme based on corrected bearings so that you can judge which angle is lying in which quadrant.

Latitude and DepartureIn order to do start with Theodolite Traversing you should be familiar with the Latitude and Departure which are discussed briefly below, OA is the line with whole circle bearing equal to θ. OC = Latitude = lCosθ OB = Departure = lSinθ By using the above formulae for Latitude and Departure with whole circle bearing, calculator will be giving algebraic sign automatically for Latitude and Departure. For a closed Traverse ∑ of all Latitude is equal to zero and ∑ of Departure is also equal to zero. Consecutive co-ordinatesWhen the Latitude and Departure are calculated at second point of a given line taking first point as a origin then it is called consecutive co-ordinates. Independent co-ordinatesIndependent co-ordinates are the Latitude and Departure of points of a traverse with respect to a common origin, so that all the values are +ve. These are used for plotting purposes. Bowdich RuleThis rule is used to apply the correction in Latitude and Departure which states that correction in Latitude/Departure is equal to Length of Line multiply by Total correction in Latitude/Departure and then dividing by the perimeter. Traverse TableFor the following traverse ABCD, I have applied the correction in Latitude and Departure using Bowdich rule. Line L (m) Bearing (° ′ ″) Latd. Depr. Corrections applied Consecutive co-ord. Independent co-ord. Latd. Depr. Latd. Depr. Latd. Depd. AB 148 115 30 -63.27 133.58 -0.26 - -63.98 133.58 500 500 BC 172 42 25 126.98 116.02 -0.30 - 126.68 116.02 628.68 616.02 CD 201 205 30 -181.42 -86.53 -0.36 - -181.7 -86.53 444.90 529.49 DA 202 306 15 119.44 -162.9 -0.36 - 119.08 -162.9 563.98 366.59 ∑ 723 +1.28 +0.17 -1.28 0 +0.17 As you can see, correction was not applied in Departure as the error was too small to be neglected. Using Bowdich rule we can apply correction in Latitude and Departure for respective line