A- Topographic Surveys

Topographic Surveys are used to identify and map the contours of the ground and existing features on the surface of the earth or slightly above or below the earth’s surface (i.e. trees, buildings, streets, walkways, manholes, utility poles, retaining walls, etc.). If the purpose of the survey is to serve as a base map for the design of a residence or building of some type, or design a road or driveway, it may be necessary to show perimeter boundary lines and the lines of easements on or crossing the property being surveyed, in order for a designer to accurately show zoning and other agency required setbacks.
Topographic surveys, may be required as part of real estate transactions, civil engineering design and construction projects, including:
Road or bridge design or improvements.
Grading or drainage projects.
New construction.
Remodeling projects to existing structures.
Utility design.
Topographical land surveys or geomatics, as it is becoming known, are carried out with the use of the latest Leica Instrumentation linked to full keyboard data logging equipment for fast and accurate data collection. All of our instruments have the facility of remote surveying with the use of those hard to reach places.

Purpose

The preliminary survey is a relatively large scale instrument survey conducted for the purpose of collecting all the physical information which affects the proposed location of a new highway or improvements to an existing highway. In the case of new roads, it consists of running an accurate traverse line along the route previously selected on the basis of the reconnaissance survey. In the case of existing roads where only improvements are proposed, the survey line is run along the existing alignment. During this phase of the survey, topographic features and other features, like, houses, monuments, places of worship, cremation or burial grounds, utility lines, existing road and railway lines, stream, river, canal crossings, cross-drainage structures, etc. are tied to the traverse line. Longitudinal-sections and cross sections, are taken and bench marks established. The data collected at this stage will form the basis for the determination of the final center line of the road. For this reason, it is essential that every precaution should be taken to maintain a high degree of accuracy.

Besides the above, genial information which maybe useful in fixing design features within close limits is collected during this phase. The information may concern traffic, soil, construction materials, drainage, etc. and may be collected from existing records as through intelligent inspection/simple measurements. Detailed investigations dealt with in section 10 through 16 are not envisaged at this stage. It may be found convenient to divide the road into homogeneous sections from traffic consideration and prepare a typical estimate for one km stretch as representative of each homogeneous section. With the data collected, it should be possible to prepare rough cost estimates within reasonably close limits for obtaining administrative approval, if not already accorded and for planning further detailed survey and investigations. particular, information may be collected regarding :-

(i) The highest sub-soil and flood water levels, the variation between the maximum^ and minimum, and the nature and extent of inundation, if any, gathered from local enquires or other records. These should be correlated to data about the maximum and minimum rainfall and its duration and spacing, etc. by appropriate hydrological analysis.

(ii) The character of embankment foundations including the presence of any unstable strata likes micaceous schists, poor drainage or marshy areas; etc. This is particularly necessary in areas having deep cuts to achieve the grade.

(iii) Any particular construction problem of the area, like, subterranean flow, high level water storage resulting in steep hydraulic gradient across the alignment canal crossings- and their closure periods. Information regarding earlier failure? in the area of slides or settlements of slopes, embankments and foundation, together with causes thereto may also be gathered from records and enquiry where feasible.

(iv) In cut sections, the nature of rock i.e., hard, soft etc. should be determined by trial pits or boreholes. This is essential to make realistic cost estimates.

Survey Procedure

1. The preliminary survey starts with running of a traverse along the selected route, adhering as far as possible to the probable final center line of the road. In difficult situations, a secondary traverse connected to the primary one at either end may also be run. In hilly areas, a trace cut 1.0 to 1 .2 m wide, if required may be made during the preliminary survey. For details in this regard, reference maybe made to IRC:52 'Recommendations About the Alignment Survey and Geometric Design of Hill Roads".

2. The traverse consists of a series of straight lines with their lengths and intermediate angles measured very carefully. In difficult terrain, the alignment may have to be negotiated through a series of short chords, preferably, done with a theodolite with Electronic Distance Measurement (EDM) and all angles measured with double reversal method. Global Positioning System (GPS) is also very useful and appropriate for preliminary survey. The GPS will give locations in co-ordinates all the necessary points on the traverse. GPS is very fast reasonably accurate for preliminary system and computer friendly for data transfer. Control pillars in cement concrete should be fixed at suitable interval (ranging from 500 m to 2 kms) to have control on accuracy. It also helps in repeating the survey, if required, within the control pillars.

3. Distances along the traverse line should be measured with EDM or total station An accuracy of at least 1 in 10000 should be aimed at mall distance measurement.

4. No hard and fast rule can be laid down as regards distance between two consecutive transit stations^ In practice, the interval will be dictated by directional changes in the alignment, terrain conditions and visibility. The transit stations should be marked by means of stakes and numbered in sequence. These should be protected and preserved till the final location survey.

5. Physical features, such as, buildings, monuments, burial grounds, cremation grounds, places of worship, posts, pipelines, existing roads and railway lines, stream/'river/canal crossings, cross-drainage structures, etc. that are likely to affect the project proposals should be located by means of offsets measured from the traverse line. Where the survey is for improving or upgrading an existing road, measurements should also be made for existing carriageway, roadway and location and radii of horizontal curves. In case of highways in rolling and hilly terrain the nature and extent of grades, ridges and valleys and vertical curves should necessarily be covered. The width of land to be surveyed will depend on the category of road, purpose of the project, terrain and other related factors. Generally, the survey should cover the entire right-of-way of the road, with adequate allowance for possible shifting of the center line from the traverse line.

6. Leveling work during a preliminary survey is usually kept to the minimum. Generally, fly levels are taken along the traverse line at 50 meter intervals and at all intermediate breaks in ground. To draw contours of the strip of land surveyed, cross-sections should be, taken at suitable intervals, generally 100 to 250 m in plain terrain, upto 50 m in rolling terrain, and upto 20 m in hilly terrain. To facilitate the leveling work, bench marks, either temporary or permanent, should be established at intervals of 250 to 500 meters. The levels should be connected to GTS datum.

7. Field notes of the survey should be clear and concise, yet comprehensive enough for easy and accurate plotting.

8. Apart from traverse survey, general information about traffic, soil, drainage should be collected while the traverse is being run, as mentioned in para 2.

Map Preparation

1. Plans and longitudinal sections (tied to an accurate base line) prepared as a sequel to the preliminary survey are referred to for detailed study to determine the final center line of the road. At critical locations, like, sharp curves, hair-pin bends, bridge crossings, etc., the plan should also show contours at 1-3 meter intervals, particularly for roads in rolling or hilly terrain so as to facilitate the final decision.

2. Scales for the maps should generally be the same as adopted for the final drawings. The following scales are suggested:

(i) Built-up areas and stretches in hilly terrain- 1 : 1,000 for horizontal scale and 1 : 100 for vertical scale.

(ii) Plain and rolling terrain- 1 : 2,500 for horizontal scale and 1:250 for vertical scale.

3. For study of difficult locations, such as, steep terrain, hair-pin bends, sharp curves, bridge crossings, etc. it may be convenient to have plans to a larger scale than recommended above. If necessary these plans may show contours preferably at 2 m interval, though this could be varied to 1.5 m according to site condition.

Traffic Survey

SPT was generally be conducted in boreholes at interval of 1.5 m. The tests were conducted as per IS-2131. For conducting the test, the bottom of the borehole was properly cleaned and split spoon sampler was properly seated in position in the borehole.
The test is basically a penetration test in which, a thick wall split tube sampler, shall be driven into the undisturbed soil at the bottom of the hole under the blows of a 63.5 kg drive weight with 75 cm free fall. The sampler shall be first driven through 15 cm as a seating drive. It shall be further driven through 30 cm in two stages of 15 cm each or until 100 blows have been applied. The number of blows required to drive the sampler in second and third stage for penetration of 15 cm each (total 30 cm) beyond the seating drive shall be termed as “Penetration resistance N”. The samples collected shall be used as disturbed soil samples for laboratory testing. The split spoon sampler shall conform to IS 9640-1980.
In case the blow count of SPT in soil (including the number of blows for seating) exceeds 100, the corresponding penetration was recorded and this particular test at that depth stopped.