What is A Topographic Survey?
A topographic survey is an Engineering survey to understand and analyze the ground features along the proposed alignment. By applying mathematical principles to the Survey data, existing or future horizontal and vertical position will be determined. The main objective of topographic survey for a road is to create a digital terrain model (DTM) by acquiring terrain data. Survey activities include road alignment, fixing center line of road, providing permanent grid lines and benchmarks as per the applicable standards.
The topographic survey helps the engineers to:
- prepare alignment drawings
- prepare cross-sectional profiles
- identify existing structures in the proposed road alignment
- finalize requirement of bridges, culverts, diversions etc.
- plan land acquisition requirements
- establish control of locations
- establish elevation difference between fixed points
- identify the presence of underground utilities like pipelines, electrical cables etc.
Purpose of this Method Statement
This method statement describes the procedure and resources required to do the work. Use any other resources and methods not referred to in this method statement to suit the project requirement. Always execute the work safely complying with the required standard.
This method statement summarizes suggested method of executing works safely within any constraints. This method statement offers advice and guidance to the personnel involved in this activity to:
- Carry works in a manner that’s safe at all times;
- Know the hazards involved in the activity;
- Ensure controls to steer clear of hazard exposure are in place.
The sequence of activities is a repetitive process and many aspects are common to distinct sites. Include with detail, any crucial aspects specific to the project. Always follow the approved checklists prior to the start of the activity.
What this Method Statement covers
The scope of this document covers
- A safe work method for performing a topographic survey
- Topographic survey for road work procedure
- Materials, equipment, and tools needed to carry out the activity
- Applicable standards to execute the work
- Specifications for Road and Bridge Works published by Indian Roads Congress
- IRC:SP : 19-2001 : Manual for Survey, Investigation, and Preparation of Road Projects
Equipment & Tools for topographic survey
- Total station with appropriate software
- Electronic distance measurement (EDM) reflectors
- Differential Global Positioning System (DGPS)
- Auto level and level staff
- Measuring tape
- Range poles
- Level Rods
- Digging Tools
- Pegs and nails
- Paint and paint application tools
Health, Safety, and Environment
Execute all activities with due regard to Health, Safety & Environment of all the employees and third parties.
- All persons involved in the survey activity must wear reflective vests and identity cards
- Provide adequate flaggers, warning taps and safety cones as required
- Make the necessary arrangement to provide drinking water
- Provide vehicle and cell phones as required
- DO NOT expose telescope to the sun
- DO NOT carry instrument along with stand
- DO NOT keep battery inside the instrument when the instrument is inside the box
Personal Protective Equipment (PPE)
Find more details about Personal Protective Equipment (PPE) here.
- Ensure valid calibration certificates for auto level and total stations through authorized agencies.
- Follow approved survey checklist
- Non-closures of own measurements and combined with the previous surveys shall meet the specified requirements.
- The data should be in a form amenable to digital terrain model (DTM) commonly used by highway design software like MXROAD Suite, AutoCAD Civil 3D or equivalent).
Procedure for Topographic Survey
- Collect Great Trigonometrical Survey (GTS) Bench Mark data along the road sections
- All reference pillars shall be of M20 grade of size 20 cm x 20 cm x 45 cm height. Fix a 10 mm dia steel bar inside the concrete pillar. Fix the pillars on a firm ground embedded in M15 grade PCC up to a depth of 30 cm and 5 cm wide all around. Paint the rest 15 cm of pillar above the ground with yellow color paint.
- All control point pillars namely horizontal control points and the benchmarks shall be of an M20 grade of size 20 cm x 20 cm x 60 cm height. Fix a 10 mm dia steel bar inside the concrete pillar. Fix the pillars on a firm ground embedded in M15 grade PCC up to a depth of 45 cm and 5 cm wide all around. Paint the rest 15 cm of pillar above the ground with yellow color paint.
- Fix horizontal control points using DGPS instrument at every 5 km.
- Establish Bench Mark (BM) stations at every 250 meters interval. Use double run leveling method with digital auto levels.
- Fix all cardinal points like horizontal intersection points (HIP), center points and transit points etc. with a pair of reference pillars fixed on either side of the center line at safe places within the ROW.
- Take spot levels at every 25 m interval for cross-sectional Topographic survey
- Establish reference center line and mark the same by nails on the ground. Mark by paint for the existing road surface. Take the spot levels at every 25 m interval along the center line for longitudinal Topographic survey
- Other physical features
Capture details of all existing structures like
- major bridges, minor bridges, culverts
- utilities present underground or overhead – electrical lines, gas pipelines, OFC etc.
- presence of water bodies
- religious structures
- Any other structure of significance
The details shall include location, chainage, invert level etc.