Structural Community

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

The following points should be kept in mind while selecting pipe for a certain water supply system, Carrying capacity. Durability. Fire cost. Maintenance cost. Type of water to be conveyed. 1. Cast iron pipes (C.I)Most widely used for the city water supplies. Average life is 100 years. Corrosion my reduce its capacity by 70%. Must be lined with cement or bitumen. C = 130 for new pipe. C = 100 for old pipe (Selected for Design). "C" is the Hazen Williams Coefficient known as HWC. It is the important term used in the design of water distribution system. 2. Steel pipesContains less carbon than Cast Iron pipes. Frequently used for trunk mains. Difficult to make connections hence seldom used for water distribution systems. Much Stronger and lighter than Cast Iron pipes. Cheaper than Cast Iron pipes. Cannot withstand vacuum, hence collapse. Highly susceptible to corrosion, hence high maintenance charges are required. 3. Ductile pipesSimilar to Cast Iron pipes except increased ductility. Ductile iron is produced by adding a controlled amount of Mg into molten iron of low sulphur and phosphorous content. Stronger, tougher and elastic than Cast Iron pipes. More expensive than Cast Iron pipes. 4. Galvanized iron (G.I) pipesManufactured by dipping Cast Iron pipe in molten zinc. Resistant to corrosion. Mainly used for plumbing. 5. Concrete pipesUsual size of Reinforced Cement Concrete pipe is 400mm dia. and above. Not subjected to corrosion. Manufactured at or near site. Average life is 75 years. C = 138 to 152. 6. Asbestos cement pipes (A.C)Sizes are 100mm to 600mm dia. Average life is 30 years. Immune to actions of acids, salts, soil and corrosion. Less cost for laying and jointing. Less plumbing cost due to less friction. C = 140. Asbestos Cement pipes are economical and are generally preferred to use in the design of water supply systems. 7. Poly vinyl chloride pipes (PVC)Mainly used for domestic plumbing. Easy to install and easy to handle. Cheaper in material cost Weak to sustain load. Only available 350mm dia size. Expected life is 25 years.

Leveling equipmenta) LevelThere are different types of Levels as follows, 1. Dumpy levelIt is the type of Level in which whole body of level is cast in one unit. 2. Tilting levelStill being used, Level can be tilted in vertical plane with the help of tilting drum. 3. Automatic levelIn this type, the line of sight becomes horizontal when the Level is within certain limits. This system provides the works on the principal of gravitation. b) StaffIt is the graduated rod of maximum 5m length usually available in telescopic form. The gradations are both in feets and meters. Smallest graduation in feet is 0.01 ft or 1/100 ft and smallest division in meters is .005m. Technical terms in leveling1 - SightsA reading taken from a level on staff is called sight. 2 - Back sight (B.S)It is the first sight taken after setting of the instrument. 3 - Fore sight (F.S)It is the last sight taken before shifting the instrument. 4 - Intermediate sight (I.S)These are sights taken between F.S and B.S. 5 - Line of collimationIt is the straight line joining the intersection of cross hairs and optical center of object glass. 6 - Level lineIt is the curved line equidistant from the center of earth at all points. 7 - Horizontal lineIt is the straight line tangent to observer position. The of collimation obtained by a carefully leveled instrument is a horizontal line. 8 - Reduced level (R.L)It is the level of a point with respect to a certain datum whose level is taken as zero. 9 - DatumIt is a certain reference level to which levels of all other points are referred i.e in Pakistan Datum is mean sea level (MSL) at Karachi. 10 - Change point (C.P)It is the last position of staff after which the instrument was shifted.

A tunnel is an elongated, narrow essentially linear underground opening with a length greatly exceeding its width or height. Most tunnels are nearly or exactly horizontal but for special purposes, tunnels may be driven at angles up to 30 degrees from the earth's surface. The one which is greater than 30 degrees from horizontal are designed as shafts. When rocks in tunnels are highly in-competent, especially when underground water is present, tunneling becomes a very costly and hazardous operation, and excavation and containment of such rocks present a challenge that requires maximum use of highly technical skills and ingenuity. History of tunnelingThere is abundant archaeological evidence that in Europe stone age man sank shafts and drove tunnels to recover flint for the fabrication of sharp-edged implements such as knives, axes etc. later as an elementary knowledge of metallurgy was acquired by premature people, possibly for the first time central Asia, underground excavation became necessary to supply the increasing demands for metals and alloys. Very early underground excavations for metal-bearing have been identified in Caucasia, between the Black and Caspian Sea, and date back to approximately 3500 BC. Many tunnels were built in ancient times by the Babylonians, Indians, Persia and Egypt in search for precious metals. Stone-age man used very primitive tools in underground excavation. Particularly useful to him were picks made of deer antlers, flint axes and hammers and wedges made of bone and wood. The production of metals and alloys provided materials for increasingly efficient rock excavation. Later on, explosives were used in the seventeenth century. For hundreds and perhaps thousands of years underground working in hard rocks, especially those containing few fractures and fissures, were advanced by building fires against rock faces to cause expansion and spalling. In some operations spalling of the heated rock was accelerated by dowsing it with water. The fractured rock was than separated from the working face with picks, gads and wedges. With the increasing use of explosives first the black powder later nitroglycerin, steel temping techniques were perfected and permitted efficient and economical hand drilling of holes for explosives. Tunneling machines have been used to excavated tunneling with diameters of about 6 ft to more than 36 ft. Rate of excavation of over 400 ft per day have been recorded in soft ground. In hard rocks it can be less as 100 ft per day. It includes a rotating cutter head and provision for controlling forward thrust and alignment. In the hardest of rocks, near the middle of the nineteenth century steam powered piston drills and later percussion drills, powered by compressed air, made their appearance and at the same time several tunneling machines such as moles were invented. Tunnels have been driven in a variety of natural materials ranging from unconsolidated water-soaked clay, sand and gravel to dry very hard un-fractured rocks. It is one of the costliest and at the same time one of the most hazardous of all engineering under-takings. In case of long tunnels in area of geological complexity, all types of uncertainties arise, including design and construction techniques and including estimate of cost. The location of a tunnel like the site of bridge often does not allow much freedom of choice. It becomes necessary at given place to maintain an alignment. Before designing and planning a tunnel the undesirable underground conditions must be anticipated. Tunnels through massive un-fractured granite or through horizontally layered sandstones that are well cemented and un-joint present no special problems in design and preparation of cost estimation, whereas in geological complex areas it is an art and intelligent guess work. Purpose of tunnelingTunnels have been constructed for great variety of purpose, and they are classified as follows: Tunnels driven to gain access to economic mineral deposits and to provide haul-ways for extracted minerals. In some mining operations tunnels are driven to provide adequate circulation of air in underground workings. Transportation Tunnels, including pedestrian highness navigational and railroad tunnels. These are among the largest and at time the most difficult of all tunnels to excavate. Water or Sewage Tunnels: These tunnels may or may not be constructed so as to transport liquid under pressure, and a distinction is made between gravity flow tunnels and pressure tunnels. The latter are designed to contain without leakage water under hydrostatic pressure or force-pressure head. Military Tunnels: These tunnels are driven in connection with underground military operations. Tunnels to provide protection from atomic explosion. Utility Tunnels. Built to contain power and communication transmission line, gas line, etc.

Tunnel sectionsTunnels range in dimensions of cross-sections from those of small galleries driven by miners working with hand tools, to tunnels large enough to accommodate railroad trains, double lane of highway traffic, or to transport very large volume of water as in diversion structures in dams. A minimum size of tunnel is 9 ft high and 4 ft wide at the working face. Designed shapes or sizes of tunnels in x-section conform to a planned uses to tunnel and some extent to the nature of the material that is anticipated will be encountered during excavation, x-sectional shapes vary from square or rectangular as for example in mining operations in strongly bedded sediment rocks, to circular. A common type of x-section is horseshoe shaped to provide maximum stability in the roof portion of the tunnel. Geological explorationThe geological conditions that are likely to meet in any given work of construction must be predicted. The line of the tunnel and the neighboring ground is geologically surveyed and sub-surface data obtained by exploratory boring. Careful control of such trial boring operations is necessary in order to extract the maximum amount of information from the ground. The cost of tunneling in general is least where construction is carried out in sound rock, and in one kind of rock throughout. Straight forward geological conditions such as simply dipping strata allow cost to be estimate easily; more uncertainties arise in connection with folded and faulted beds. Geological structures such as faults and joints should be mapped along the line of a tunnel. Strongly developed joints systems are potential channels for underground circulation and should be recorded. Badly fractured ground is to be avoided if possible. If unavoidable it may require special timbering or other treatment, and a prediction of where faults are likely to meet underground is therefore of greater importance. Hard rocks where excavated may stand with little support (some tunnels are unlined throughout) because they are strong enough to withstand the lateral pressure exerted by surrounding rocks but if soft bands are present there may be a tendency to slipping on these weaker layers and suitable support for the walls of the excavation will be necessary. Inter- bedded hard and soft rocks, such as sand-stones and shales may give rise to many difficulties. Ground-water percolating through the sand-stones soaks into the shales and softens them and hence the slipping is promoted.