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PURPOSES OF SERVEYING
- Determining exactly the location of the items of construction
- Assessing specifically topographical conditions that need to survey, on that basis, proposing construction methods.
- Determining relatively accurate embankment volume of works, serving for design and construction.
- In addition, for important projects, in the process of construction and project operation, it is also necessary to monitore displacement of settlement, tilting to assess degree of stability and overcome timely if it exceeded allowed limitation.
With a team of experienced geological engineers and high skilled workers, Polycons will certainly bring to customers the survey results with the most reliable precision
II. SURVEYING SCOPE
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Topographical Surveying:
Surveying scope:
- Controlling the surface and controlling height
- Measuring the construction ground plot.
- Measuring longitudinal profile and horizontal profile
III. METHODS
1. Topographical surveying:
a. Controlling height:
- From the Hon Dau national high point system, measuring the height to construction site by 3rd-grade, measuring on and on about 5Km.
- National height will be measured and connect to all controlling coordinates points in the area.
- Measuring equipments: Leica NA2 Optical leveling machine, degree of accuracy 0.7mm/Km (used with normal pole) or Leica DNA03 Electronic leveling machine, degree of accuracy 0.9mm/Km (used with normal pole). Leveling pole 4m.
- The 3rd-grade will be measured on and on, closed loop error ≤ 10√L (mm), L is length of line in Km.
- Measuring adjustment closely by PVV = min method.
b. Controlling ground:
b.1. Measuring to link national coordinates VN2000 system:
- Measuring and establishing 2 points of national coordinates VN2000 system by GPS, degree of accuracy equivalent to 1st-level transmissions.
- Measuring equipment 1 frequency GPS machine, measuring time of 1 case is ~ 1 hour, degree of accuracy 5-10mm
b.2. Construction of grid to control the coordinates of area
- From 2 GPS points, establishing 1 area coordinates grid includes 4 points of 2nd-level transmissions, cover on all of area.
- Measuring equipments: Using Leica Total Station TC1800 Power, degree of accuracy for angle measurements 1’’, degree of accuracy for edge measurements. The machine is tested and calibrated exactly, the mirror is placed on the base plate with the optical projector mounted on the tripod
- Methods: Angle measurement 2 rounds (normal and reversed glass), the edge is measured 2 times, measuring on and on. Angle measurement error ≤ 12 ", closed edges relatively error reaches 1/10000.
- Controlling mark: iron rod ф10, length 1.2m which is embedded land deeply, on surface, concreting a block of concrete size 30x30cm, thick 20cm, mark is high as land surface.
- Measuring adjustment closely by PVV = min method.
c. Planimetric Survey:
- The Work of measuring height plan were performed by Leica Total Station TC405, TC307 Power
- Details Points which are measured includes: roads, electric poles, culverts, houses, fences…Height points are measured averagely ~5-10m/point. The topographic and geophysical points are drawn in topographic map symbols
- Height of manholes and bottom slab of drains in front of construction.
- Current status of construction Drawings will be drawn on PC by ACAD R2004 software.
d. Measuring longitudinal section:
The measurement points details shows the changing topography, materials of construction; distance measuring points must comply with standards and regulations; for special topography or sudden change is measured follow that topography, regardless of distance and must reflect the length of construction , distance and location of the cross section, the main characteristics of construction…
e. Measuring horizontal section:
Distance measuring points details may not exceed 23m; with special topographical distance measurement points can be shorter. For the special topography or sudden change is measured that topography, regardless of distance. The measurement points shows the changing topography and materials and the main characteristics of construction…
Machine is placed at the piles that were identified on the lines, Carrying out measuring the line horizontal section: Noting the measurement direction of sections must be perpendicular to constrution which need to survey and design:
f. Casting and deepening height mark:
Just 100m deepen 1 height mark. Mark size: 12x12x40 cm
2. Equipments is used for Topographical Surveying
Equipments is used for topographical surveying, must be tested to ensure technical requirements for the topographic survey.
