The survey is carried out from the starting point to the end point by following the sequence given below:
MoRTH Clause No: 109 and technical specifications of the project shall be followed.
For the above task, the following precision survey instruments are used to maintain the required accuracy:
Project reference center line of the proposed cross-section shall be fixed by the surveyor and marked on the ground using nails. Chainage shall be clearly marked on the existing road using paint.
This marking shall be carried out at an interval of 20 m on straight portions and 10 m on curved portions. Offsets shall also be marked on the existing road wherever applicable.
Further, prior to the commencement of earthwork or structural work, as per MoRTH specification Clause 109.3 and 109.5, the centerline shall be referenced by providing chainage pillars at the Right of Way (ROW) edge.
The survey is carried out for fixing of the control network. The following methodology is based on the measurement of angles and distances on a horizontal plane along with satellite geometry.
Great Trigonometrical Survey (GTS) points are already established by the Survey of India with reference to Mean Sea Level (MSL).
Initially, pairs of ground control points are established at every 5 km interval. These points are connected to the DGPS network to obtain accurate X, Y, Z coordinates for the entire project.
Auto level instruments are used to determine the relative difference in elevation between two points. The survey is carried out between fixed DGPS datum points to identify misclosure in height.
Precision automatic levels, conforming to MoRTH Clause 900 and fitted with micrometer attachments, shall be used for all double run and TBM transfer works to ensure accuracy.
Precast pillars of size 150 mm × 150 mm × 750 mm, reinforced with 6 mm bars and provided with a central 8 mm rod (marked with a dot on the top surface), are used as TBM pillars.
These pillars are embedded such that 300 mm remains above ground level. Yellow, black, and red paints are used for marking their identification name and number.
Traverse stations are marked by fixing a nail at the center and highlighting it with a yellow paint mark on one edge of the existing carriageway surface at every 250 m interval. Each station is assigned a unique identification number.
The laid out reference line is taken as “0”. On the longitudinal section (L-section), cross-sections are taken at specified and prescribed offset distances on the original ground.
Levels are observed at every 10 m interval in the longitudinal direction and up to PROW in the cross-sectional direction.
The RLs (Reduced Levels) of OGL are observed and calculated from a known station and closed on another known station to ensure accuracy.
Internal calibration shall be carried out once every month for leveling instruments and total stations in specified formats.
Calibration certificates for level instruments and total stations must be submitted with valid certification from the manufacturer.
A “Survey File” containing necessary data such as DGPS details, traversing details, horizontal and vertical control points, reference pillars, survey monuments, and horizontal alignment setting-out details shall be submitted to the Client/Engineer.
The responsibility for implementation of this procedure lies with the surveyors deployed at various sections for different activities, along with the Survey Engineer and Section In-Charge.
