S
Horizontal controls involve in location of ground control points. These ground controls points cover the complete area to be surveyed. The boundary of the area to be surveyed can be found out by horizontal control. Horizontal control forms a frame or skeleton of survey of required terrain from which other details and contours can be located. "Working from whole to part" is the fundamental principle of surveying. Excessive error which may be accumulated, can be prevented by following the fundamental principle strictly. For establishing the horizontal control, there are two common methods employed into the surveying work are as follows: Triangulation Traversing Methods If the area is small, then only single station is taken in the horizontal control. The other points of the area involved in the boundary can be connected to the single station by measuring relative distance and direction which further forma the triangles. If the area is very large, then a traverse or series of connected traverses are involved in the horizontal control. Stadia survey is used for an uneven area. If the area is more extensive, then it is feasible to employ the survey into two system of horizontal control. The method of finding the elevations of various ground features is termed as vertical control. The frame work or skeleton of the area is formed by vertical control. Vertical control is very important because topographical map shows 3D or 3-dimensional relationship or relief of a required area. The main purpose of vertical control is To find the elevations of primary control points To establish bench marks (B. M.) at convenient interval. Bench marks covers the entire area so as to start the levelling operations from starting to end and bench marks also used as reference points for any future work The primary vertical control is done by running high order spirit levelling circuit for the survey having more larger areas The levelling work is possibly done on level or gental slope area The secondary vertical control is established by finding the elevations of traverse station and bench marks near to the station. The secondary vertical control can be done by tacheometric survey or spirit levelling. With the help of levels, the elevation of control station can be found out by running levelling circuits. Note that, it is important to establish the bench mark in such way that bench marks can be observed from nearby horizontal control points Degree of accuracy in case of vertical control varies from 10 √K mm to 20 √K mm in which K distance in km' The conventional method to check the verticality of the building is the use of plumb bob. The plumb bob is the most commonly used tool for maintaining verticality of the building. Verticality of the building can be maintained by two plumb bobs at the end of each face of a building, extending upto a fixed height from the base of the tower so that, same reference points are used at all times which give the best result of maintaining verticality of tall buildings. In advanced method, total station can be used for monitoring the northing and easting of the four corners of the building at each level. To do this, four reference pillars or fixed station are to be established on the ground away from the tower from where the corners of the building can be viewed through the telescope of total station till the building reaches its total height. Verticality of tall or high-rise building can also be done by laser beam. The laser plumb can be used for measuring the deviation the transmitter is fixed at the base and the target glass plate is attached to the moving form work. This method is used in the construction of circular silos, chimneys where the slip form method is used for raising the R.C.C tower. A field survey party examines the general character of a fairly broad stretch of land between the terminal stations in the field, along the proposed alternative alignments marked on the map is known as reconnaissance survey. In this survey, simple survey instruments like prismatic compass, abney level, tangent clinometer, barometer etc. may be used to collect additional details rapidly. Objects: To collect the details of obstruction along the route which are not available in the map. For example, valleys, ponds, lakes, marshy land, ridge, hills, permanent structure etc. To collect geological features of field. For example, soil type along routes from field identification tests and observation required for the foundation work of bridges of road pavements. To collect information regarding the availability of local construction material, water and labour. To determine the approximate values of gradient, length of gradients and radius of curves of alternate alignments. To locate the obligatory points along the alternative routes. To determine approximate estimate of the total cost of construction of the road along each route. To determine two or three best possible routes. Defination: The art of finding the details of alternative alignments found suitable during the reconnaissance survey is known as preliminary survey. In preliminary survey, the survey instruments to be used are chain tape, prismatic compass, levelling instrument, plane table, theodolite. To survey along the various alignments found after the reconnaissance and to collect all necessary physical information and details of topography. drainage and soil. To compare the different proposals in view of the requirements of a good road alignment. To estimate the cost of constructing the road including bridges and other construction aspects along each alternative alignment of the road. To finalise the best alignment from construction, maintenance and traffic operation point of view. Defination: The detailed examination of the field along the alignment finally recommended during the preliminary survey is called location survey. In this survey instruments used are theodolite, level, plane table, tape etc. The alignment finalized at the design office after the preliminary survey is to be first located on the field by establishing the center line The detailed survey should be carried out for collecting the information necessary for the preparation of plans and construction details for the highway project. To determine total cost of the road project. Locating centre line of the tunnel on ground. Constructing the shafts over the centre line. Transferring the alignment to inside of the tunnel. After fixing the route for the tunnel, its centre line (alignment) is accurately set out on the hills or ground. When the length of tunnel is small, the centre line can be located by means of theodolite. When the tunnel is long, and to be constructed under high mountains, the centre line is set out by triangulation preferably with the help of a micrometer transit theodolite. In the ground, pegs are driven at regular intervals and centre line is marked. If it is not possible to drive pegs into the ground, the surface of the rock pointed white and centre line is marked with black paint on it. The alignment is then finally set out by permanent monuments of stone or concrete. After locating centre line, shafts are constructed at regular interval. After constructing the shafts, the alignment of the tunnel is to be transferred down the shafts. For this, two small pillars are constructed on opposite edges of the shaft along the centre line of the tunnel. On the top of these pillars, the points corresponding to the centre line are correctly marked and wire is then stretched between them. Two plumb bobs are suspended inside the shaft as shown in above figure. By lowering both plumb- bobs to the bottom of the shaft, two points are marked. The line joining the points represents the centre line of the tunnel marked on the ground. This line is further extended into the tunnel, as work advances, by a theodolilte placed in the shafts as shown in Fig. Position of any object on the surface of the earth can be determined by spaced based positioning system (SBPS). SBPS receivers determine the position of any object existing on the surface of the Earth by trilateration of microwave signals from satellite moving in the orbit of the earth at an altitude of 20200 km. Tracks of a journey can automatically be recorded into the GPS receiver’s memory and can sub sequentially be downloaded onto the computer as a basis for drawing. sculpture or animation. Note that this track of journey may be on the surface (e.g., walking) or taken in three dimensions (3D) (e. g. while flying). It is important to note that the SBPS is the only fully functional global navigation satellite system. The satellites moving in orbits transmit precise microwave signals and the system enables a SBPS receiver so as to determine its location, speed, direction and time. SBPS is now-a-days used in navigation worldwide and it is very useful tool for map-making, land surveying, commerce and scientific uses. GPS also provides a precise time reference used in many applications including scientific study of earthquakes and synchronization of telecommunication networks. Definition of SBPS: Spaced based positioning system (SBPS) technology is a fast and accurate method of determining the location of any point of interest anywhere on the face of earth of any time during the day or night. The technology collects and processes signals from satellites in orbit around the earth to determine the location of points of interest on the ground. The basic principles of GPS are very simple. The GPS works on five fundamental concepts. These concepts are as follows. This system is based on Triangulation from satellites. For Triangulation, the GPS receivers measure the distance, for which the travel time of the radio message from the satellite is used. It needs to use a very high precision clocks, to measure the travel time (to measure the distance After the measurement of the distance the location of the satellite becomes important. There is a time lag as the GPS signals travel through the ionosphere (upper layer of the atmosphere above the stratosphere layer) from transmitting the signal by satellite and receiving the same by the receiver. Single Frequency Dual Frequency GAGAN system is an Indian Satellite Based Navigation Augmentation system. The GAGAN provides a civil aeronautical navigation signal consistent with international Civil Aviation Organisation (ICAO). GAGAN system is jointly developed by Indian Space Research Organisation (ISRO) and Airports Standards and Recommended Practices (SARPS) as established by the GNSS Panel (i.e., Global Navigation Space System) GAGAN implementation is carried out in two phases viz: Phase I: Technology Demonstration System (TDS) phase which has the objective to demonstrate the feasibility of Space Based Augmentation System (SBAS). Phase II: Final Operational Phase (FOP): This phase is used for providing a certified satellite-based navigation system for all phases of flight by augmenting the TDS system suitably Fig. shows GAGAN satellite configuration and required ground infrastructure for final operational phase (FOP) It is an important segment since it comprises the orbiting GPS satellites or space vehicles (SV) in GPS parlance. The GPS design originally called for 24 space vehicles, eight each in three circular orbital planes. However, it is modified to six planes with four satellites each. The orbital planes are centered on the Earth and these planes are not rotating with respect to the distinct stars. The six planes have an inclination of 55° approximately with respect to Earth's equator and these planes are separated by 60° right ascension of the ascending node. 60° right ascension means the angle along the equator from a reference points to the intersection of the orbit. These orbits are arranged in such way that at least six satellites always remain within the line of sight from almost everywhere on the surface of earth. Satellites are orbiting at an altitude of 20200 km approximately with the orbital radius of 26600 km. Each satellite vehicles performs two complete orbits on each sidereal day and hence the ground track of each satellite repeats each sidereal day. The ground track repeat can be used the ensure good coverage in combat zones. Fig. shows the details of space segment. The track of satellite is well decided and the flight paths of the satellite are tracked by US air force monitoring the stations in Hawaii, Kwajalein, Ascension Island, Diego Garcia and Colorado Springs, Colorado along the monitor stations operated by the National Geospatial Intelligence Agency (NGA). The tracking information is sent to the air force space command's master control station at Schriever air force base in Colorado Springs which is further operated by the two-dimensional (2d) space operations squadron of the united state Air force. Two space operations squadron contacts each GPS satellite regularly with a navigational update by using antennas. These updates synchronize the atomic clocks on the board of satellites within a few nanoseconds of each other and adjust the ephemeris of each internal model of each satellite. The updates are produced by Kalman filter which uses inputs from the ground monitoring stations, space weather and information and also the various other inputs. It generates and transmit code, carrier phases and navigation message. Here input is navigation message and output are P code C/A code, L1 and L2 which carries navigation message. It produces GPS time. It predicts ephemeris It manages space vehicle Here input is P code observation and time and output is navigational message. It works out satellite orbit and clock parameter and passes the results to ground antennas. It gives the navigation solution. It also gives the surveying solution. Determining the boarders, making existing utilities like highway, municipal amenities photogrammetric and private site-specific projects make them more dense or compact. GIS data acquisition. Monitoring, well, soil bring and other types of sampling locations Establishing state plane coordinate or geodetic coordinates Used in 'As-built Survey and Topographic survey. Used for mine exploration Used in Baseline survey and traverse control survey or traverse verification surveys. Used in natural resource mapping Used in communication tower survey and certifications. Used in construction stakes out utilities, highways, facilities, pilling etc.
Unit - 5
Construction survey & Modern Techniques such as Space Based Positioning System (SBPS)
Q1) How to establish horizontal controls?
A1)
When the area is small:
When the area is very large:
When the area is more extensive:
Q2) How to establish vertical control?
A2)
Q3) How we can maintain verticality of tall buildings?
A3)
Q4) Explain Reconnaissance survey?
A4)
Q5) Explain Preliminary survey?
A5)
Objects:
Q6) Explain about location survey?
A6)
Objects:
Q7) Explain setting out of a tunnel?
A7) The survey work of a tunnel involves the following operations:
Locating centre line of the tunnel on ground:
Constructing the shaft over the centre line:
Transferring the alignment to inside of the tunnel:
Fig.: Transferring the alignment at the bottom of the shaft
Fig.: Transferring the alignment to inside of the tunnel
Q8) What is SBPS system?
A8)
Q9) Explain about GPS?
A9) Working System of GPS with SBPS:
Q10) What are the types of GPS?
A10) Types of GPS are as follows:
There are the basic types of survey grade systems in GPS.
Single Frequency:
This type of surveying with a single frequency system is called as 'static mode' GPS surveying.
Dual Frequency:
Dual frequency systems only require post processing when operating in static or fast static.
Q11) Explain about GAGAN?
A11)
Fig.: Configuration of GAGAN Satellite
Q12) Explain Space segment?
A12)
Fig.: Details of Space segment
Q13) Explain Control segment?
A3)
Q14) What is the importance and Role of Space Segment, Control Segment and user Segment in SBPS?
A14) Space segment
Control segment
User’s segment
Q15) Explain application of SBPS in surveying?
A15)
0 matching results found