Survey for Cross-country Pipelines Onshore Pipeline

Survey and soil investigations are among the prime activities which are carried out after an onshore pipeline is planned. An appropriately and accurately surveyed onshore pipeline route dramatically reduces the efforts required for onshore pipeline design and construction. Therefore, survey is one of the foundation activity which is carried out to firm pipeline route centreline, explore dumpsites locations and intermediate station/ terminal facilities on ground, obtaining topographic features, ground profile and soil data along the pipeline route; collection of revenue maps/ data and preparation of cadastral maps for ROU/Land acquisition purposes; collection of population density data along the pipeline route.


This article covers various requirements and purpose of following different types of surveys carried out for onshore pipelines design and construction:

1. Pipeline route centreline survey
2. Detailed pipeline route survey
3. Soil investigation surveys
4. Population density survey
5. Cadastral survey

This article also includes introduction to modern survey equipment /instruments such as DGPS, GPS, EDM, Total Station, Theodolite, Inclinometers etc. utilised for the survey of onshore pipelines.

Following criteria must be followed for the selection of onshore cross-country pipeline route to ease the design and construction of the pipeline:

The starting activity for planning an onshore pipeline is to identify the termination (i.e. start & end) location and route of the pipeline. Identification of the pipeline route, during the planning stage of the pipeline, is carried out by desktop study consisting of marking the pipeline route on low resolution digital maps available in public domain. Based on the desktop study, initial approvals are sought. After obtaining the preliminary approvals for the planned pipeline, the pipeline route needs to be physically verified by centreline survey to start the design activities.

Objectives

During the centreline survey, reconnaissance survey is carried out by the SURVEYOR using Global Positioning System (GPS) and other survey equipment such as magnetic compass, inclinometer, theodolite etc. to orient the most practical alignment along identified route using his best judgement and experience to interpret the needs for pipeline construction. SURVEYOR shall locate and identify all existing features and obstructions within a corridor of 5 km on either side of the centreline of pipeline route (identified by Owner) that are not shown in the available maps and subsequently update the local topographic maps to reflect such changes. SURVEYOR shall establish stakes/ mark flag control points on ground along the centreline of route at all major road, rail, canal, pipeline, river crossings and terminal locations. Flag control points shall also be clearly identified on the route maps by the SURVEYOR so that same can be physically verified by the Owner after submission of centreline survey documentation.

SURVEYOR shall also collect the future development plans from the concerned authorities to gauge its impact on the pipeline route and consequently pipeline during its entire design life.

Pipeline Route Recce

SURVEYOR, in general, shall avoid any major deviation from the route identified by the Owner. During the pipeline route recce, SURVEYOR shall avoid route requiring to cross obvious man made and/or natural obstructions such as culverts, bridges, utility poles, building/structures, gorges, plantations, archaeological sites, reserve forest, environmentally sensitive areas, mining sites, future built-up areas etc.

While selecting the pipeline route in an undulating area, hand held inclinometer shall be used for the estimation of slopes. Following criteria shall be taken into account while selecting pipeline route alignment in hilly or undulating locations:

1. A longitudinal slope along pipeline route shall not exceed 1:5
2. A transverse slope across pipeline route shall not exceed 1:1
3. As far as possible ridges/spurs should be used to climb up or down from hill. Side slopes of hills requiring excessive side hilling should be avoided.

Centreline alignment thus established during the recce shall be marked prominently on the route maps. Additionally, chainage in kilometers, major turning points, intermediate facilities, planned developments, existing features/obstructions, flag control points etc. shall also be marked on the route maps.

Field Marking

Entire length of the surveyed route shall be staked on the ground by the SURVEYOR along the centreline of the proposed pipeline route. Stakes shall be installed at flag control points, major crossings, major turning points and at an approximate 1.5 to 2.0 km interval as dictated by field conditions. Consideration shall also be given to land use before placing the stakes e.g. stakes placed and left in cultivated land may not be acceptable to the land owner. Stakes in such areas shall be placed at boundaries between cultivated areas where necessary. Sketches/ photographs to facilitate location of stakes on the field shall be furnished by the SURVEYOR giving reference of existing features wherever major directional change has taken place. Stakes may be 8 mm dia. painted twisted rods.

Presentation of Centerline Survey Data

Centreline survey data shall be presented in the form of following drawings/ documents:

1. Pipeline route map showing route on Topo sheets of scale 1:50,000 or 1:25,000 with a distance of 5 km width on either side of pipeline centreline.
2. Overall pipeline route map in 1:500,000 scale.
3. Ground profile drawing and ground elevation v/s pipeline chainages in MicroSoft Access software (ground elevations to be furnished on an average at every 1 km interval or at locations where major change in ground elevation occurs).
4. Route report shall consist of but not limited to following::
   • Route description
   • Topographic features
   • Major Crossing details
   • Extent of reserve forest
   • Land use pattern and soil strata along route.
   • Developments plans
   • Estimates for land cost for RoU acquisition.
   • General metrological details
   • Site photographs. (Photographs shall be sufficient in numbers to represent the entire terrain features).
   • Dump site locations suitable for pipe storage (if specified)
   • Ground Profile along the route
   • Comparison of alternative routes considered.

Above documents and drawings shall be submitted by the SURVEYOR to the Owner for their review and finalisation of the pipeline route.

Once the centreline survey activity is completed and the preliminary route is identified, it can be said in broad terms that the identified route provides opportunity for laying the pipeline. Centerline survey data is also utilised for carrying out the feasibility studies and estimation of project cost for various route alternatives of route survey so that techno-commercial viability for laying the pipeline is established and compared. However, the data obtained from the centreline survey is not sufficient enough to detail design and construct the pipeline. Therefore, detailed route survey is carried out before the start of detail engineering and construction of the pipeline project.

Objectives

The main objectives of the detailed pipeline route survey are:

• To reconfirm the pipeline alignment on ground.
• Finalize crossing locations and crossing angles.
• To obtain cross-section details and topographic features at all crossings.
• To obtain detailed topographic features within 30 m on either side of centreline.
• To obtain ground levels and/or contours.
• To determine exact pipeline route length with due consideration to ground profile of the route.
• Establish survey monuments on ground along pipeline route.
• Gather details of land use pattern and soil characteristics

Requirements

Pipeline route and turning points (TPs) along the pipeline route shall be located by the SURVEYOR in consultation with Company/ Engineer-in-charge considering the following:

1. Avoid obstructions along the line, by ranging on ground and shifting the Turning Points if need be.
2. Terrain gradient to be checked by using hand held inclinometer.
3. Ensure proper angle of crossing by keeping as nearly right angle (to road/ canals/ rail/ rivers/ streams, etc.) as possible. The right angle may be laid on ground by using a chain or string lengths in ratio of 3, 4 and 5.
4. To check from construction point of view and avoid objects like power, telephone and telegraph poles, walls, tube wells or such other structures falling in the strip of land, 30m on either side of pipeline alignment.
5. To maintain minimum distance of 100 m between two consecutive turning points.
6. Parallel Alignment: The pipeline alignment wherever runs parallel to an existing or planned under/ over ground facility will be treated as parallel alignment. For underground facilities SURVEYOR shall identify and locate them with suitable pipe locator/ cable locator. The following clearances shall be observed in case of parallel alignment defined above unless specified otherwise:
   • Between existing/ planned electrical power cables/ lines and the proposed pipeline – 50.0 metres
   • Between existing/ planned communication cables/ lines and the proposed pipeline – 25.0 metres
   • Between existing/ planned pipeline and the proposed pipeline – 50.0 metres
7. Unless otherwise stated, when the pipeline alignment runs generally parallel to a road or railway it shall be kept sufficiently clear of the Right of Way limits of the facility.

Staking of pipeline route

The pipeline defining trench centre line shall be staked by placing suitably painted marker stakes at Turning Points (TPs) and at Intermediate Points (IPs) between consecutive TPs. All Turning Points (TPs) and intermediate points are referred as Intersection Points. The pipeline centre line shall be staked on the ground as follows:

• First, the Turning Points (TPs) shall be staked on the ground. After locating and marking the TPs, the intermediate points shall be staked while measuring slack distance. The staking shall normally be done at intervals of 500 m along the centre line of the pipeline.
• The Intersection Points (IPs) shall be serially numbered from the starting point. The serial number of each Intersection Point shall be boldly inscribed on the marker stake. In addition, the Turning Point (TP) marker stake shall identify the Turning Point reference number from the starting point.
• For Intermediate Points (IPs) letter "P" shall precede the serial number of the intersection Point marker. For Turning Points, the letters "TP" shall precede the Turning Point reference number, and the letter "P" shall precede the serial number of the Intersection Point.
• The marker stakes at Turning Points (TPs) shall be referred with three reference stakes around the TP. The reference stakes shall carry the Turning Point reference number and their respective distance from the TP marker stake.
• Change in direction of line shall be marked on the TP marker stakes. In addition, direction markers near TPs and other locations shall be placed wherever necessary.

Accuracies in Measurement

SURVEYOR shall incorporate corrections to the linear ground measurement due to standard errors (and variations from standard temperature and/or pull in case of chain survey). The error for angular closure for the work shall not exceed one minute per station and for linear measurements it shall be read to the nearest 0.001 m. The error on closure for measurements on vertical distance to establish bench marks shall not be more that 24√k millimetres (where 'k' is the linear distance in km). The observations for measurement of vertical distances on bench marks shall be read to accuracy of the nearest 5 mm and for Intersection Points and other points along the pipeline route and at crossings to the nearest 10 mm. The error of misclosure in vertical distance shall be distributed linearly.

Azimuth control shall be maintained by observations of the Sun or Polaris at intervals of 15 - 20 km by closing the traverse on existing control points. These observations of bearings together with deflection angles shall be recorded in survey notes. Azimuth misclosure based on bearings with observed angles at Turning Points shall be equally distributed over the number of stations observed in between. Accuracy of azimuth observations shall be acceptable if the three deductions agree within one minute when Sun is used for Azimuth observation. In case of stars/Polaris observation, computed values should agree within 10 to 15 secs. This check is not mandatory when DGPS system is used for establishing location/ co-ordinates.

Chainage measurement

Chaining shall be continuous in the direction of survey. The true bearing of all straights shall be observed and recorded. Data regarding the nature of terrain, viz. sandy, stony, vegetation, etc. and type of ground shall also be recorded along with chainages of change points. Distance measurement shall be made by Electronic Distance Measurement (EDM) equipment (or by using 50 m steel tape or 30 m chain). However, in case of abrupt slope change the tape/chain shall be used and it shall be straightened parallel to the probable grading. Distance between Intersection Points (IPs) staked along the pipeline route should be measured and recorded. In addition, distance between level points shall also be measured and recorded. Check on distance measurements shall be by Stadia method at the time of levelling.

Measurement of Horizontal Angles

Horizontal angles are measured to indicate the change in direction of alignment and specify the horizontal bend at the Turning Points. Theodolite, reading direct to 10 seconds or better, shall preferably be used. Angles shall be measured clockwise from back station to fore-station. Mean of two readings i.e. one on face left and other on face right shall be taken as the horizontal angle. The line at both ends shall be tied to the grid control system being used for end facilities. True bearing at the beginning, end and at every 15 - 20 km shall be observed to keep a check on errors in angular measurements.

Profile measurement

Continuous profile of the proposed pipeline route shall be established from the reduced levels taken.

• at the starting point,
• at all Turning Points (TPs),
• at all Intermediate Points staked on the ground,
• at all points on the pipeline route where there is a change in slope.

All levels shall be with respect to Mean Sea Level (MSL). When the terrain is flat, reduced level shall be additionally recorded along the pipeline route at 100 m interval and when the terrain is undulating, observation of reduced level shall be made at a sufficient number of points so as to give an accurate plotting of the ground profile along the route.

For road and railway crossings: the reduced levels shall be recorded at an interval of 5 m along the pipeline alignment and at closure intervals wherever there is a change in slope within the entire width of the Right-of-Use of the road/railway.

For river/ stream/ canal crossings: levels shall be taken at intervals of 5 m up to 30 m beyond the highest banks on both sides. Levels shall be taken at closer intervals, if there is a change in slope. In right-of-use having slope across the pipeline alignment, as encountered in hilly areas, Ghat regions, ravines and other similar areas, cross-sections at 50 m interval and for a length of 30 m on either side of the pipeline alignment shall be observed and recorded.

For major water crossing sites, cross section as above shall be observed at both banks.

Method of RISE and FALL shall be used to compute reduced levels of various points. Check on computation shall be made by using the following formula:


Maximum misclosure shall not exceed 24√k mm where `k' is the distance in km. Maximum length of line of sight shall not exceed 100 m.

Co-ordinates and Grid

Differential Global Positioning System (DGPS) is used to determine co-ordinates of all intersection points and facilities along pipeline route. Accuracy of co-ordinates shall be within 0.5 metre. Non-differential or autonomous GPS are not accepted.

SURVEYOR shall submit a procedure for set-up & utilization of DGPS. All co-ordinates shall be indicated in UTM grid as well as geographic grid. In case more than one survey party is deployed, each party shall use same reference grid and DGPS system. Following information are required for the DGPS proposed by the Surveyor:

• GPS Receiver Model used
• Differential Receiver Type
• Guaranteed accuracy in metres

Levels and Contours

In addition to the elevation along the centreline of the pipeline route, ground levels within 30 m wide corridor on either side of route alignment shall also be obtained and recorded using Total Station along with the co-ordinates (in UTM grid) of each level point. All such level points shall be plotted in the planimetry portion of the alignment sheets. The levels shall be taken in such a manner that contour can be drawn with a contour interval of 5 m. Electronic data, in a format compatible with commercially available Digital Terrain Modelling (DTM) software shall be produced.

Drawing

As a minimum following drawings are prepared during detailed engineering survey:

1. Detailed Route Map (Scale 1:50,000)
2. Additional Route Map for Hilly, Ghat and ravinous regions (Scale 1:15,000)
3. Alignment sheets covering
• Right-of-Use Planimetry in UTM grid (Scale 1:2500 along the line & 1:2500 across the line)
• Ground Profile (Horizontal scale 1:2500 & vertical scale 1:250)
4. Crossing Details of Road/ Railway/ Stream/ Canal or Utility Crossings (Horizontal scale 1:100 and vertical scale 1:100)
5. Crossing details for River Crossings of width
• upto 250 m width (Horizontal scale 1:200, vertical scale 1:200)
• more than 250 m to 500 m (Horizontal scale 1:500, vertical scale 1:500)
• more than 500 m width (Horizontal scale 1:1000, vertical scale 1:1000)
6. Cross Section for sloping Right-of-Use (horizontal scale 1:100, vertical scale 1:100)

Crossing drawings are prepared using same horizontal and vertical scales as indicated above. However, in case one crossing cannot be accommodated in single sheet additional sheets may be used.

Pipeline route map shows all features including, but not limited to roads and railroads, canals, streams, lakes, rivers, villages, towns, and cities that are located within a distance of 5 km from the pipeline centre-line on either side of it. For the entire region, contours are plotted on the route map at 20 m contour interval. Additional information like cultivated areas, barren land, areas prone to flooding, rocky areas and forests including access paths/roads to Right-of-Use is also shown on the route maps. Additionally for areas which are undulating such as hilly areas, Ghat regions, ravines, and other areas, Pipeline route map to a scale 1:15,000 is drawn over a distance of 1.0 km from the pipeline centre-line on either side of it. For such areas, contours are plotted at 10 m contour interval.

Right-of-Use Planimetry drawings shows all objects within 30 metres on either side of the Pipeline in plan and spot level & contours at 5m interval.

The angle of crossing is mentioned for all rail, road, river, stream, canal and utility crossings. For rail, road, river, stream and canal crossings wider than 10 m, the distances at the start and at the end of the crossing from the nearest IP is also mentioned. For crossings less than 10 m, the distance of the centre line of crossing from the nearest IP is given.

For all river, stream and nala crossings, the level of water at the time of survey, high flood level recorded in last 100 years and the approximate surface velocity of the flowing stream (observed & recorded during survey) is reported in the survey drawings. Also, the general nature of the surface soil (soft/hard, normal soil or rock/boulders) at the bed and banks of the river/stream/nala is observed and mentioned in the drawings.

Documents

In addition to the drawings listed above, detailed survey report is also prepared indicating:

1. Details of survey methodology followed
2. Details of equipment used
3. Brief Route Description
4. Salient features of the route such as
• Total length of pipeline
• State wise distribution of pipeline route
• Terrain details and land use pattern summary
• No. of crossings (state wise & chainage wise)
• Details of River crossings
• State wise extent of forest/ reserve forest/ environmentally sensitive area
• Significant elevation changes along the pipeline route with chainages
• Nature of soil (sandy, clay, rocky, marshy, etc.)
5. Print out of information required to be submitted as data base including:
• Level & contour information for DTM
• Pipeline Profile data
• Turning Point (TP) detail

During the detailed engineering survey, one should also locate dump site(s) for storage of line pipe and other pipeline materials, along pipeline route during the construction period. Dumpsite(s) may be located at 75-100 km interval and have an area of 5 – 10 hectares. Following aspects shall be taken into account while selecting dumpsite location(s):

1. Dumpsite should preferably be a barren land free from water logging/ low lying areas.
2. The site shall be located in close proximity of identified/ established route.
3. It should be in the vicinity of Highway.
4. The site should be nearly flat with minimum undulation that might require earth work (fill-up and earth-cutting).
5. Site should not be under overhead powerlines.
6. Site should preferably be on government land.

The objective of soil investigation survey is to obtain visual engineering classification of soil and geotechnical properties of soil for design & engineering of various facilities required along the pipeline route. The soil investigation includes:

1. Boring
2. Collection of disturbed samples from bore holes
3. Visual engineering classification of soil along the pipeline route,
4. Carrying out Standard Penetration Test (SPT) at specified locations and
5. Testing the soil samples at laboratory for specified engineering properties

Location of Bore Holes

Boreholes shall be made at an interval of 250 m along the pipeline route, at all intermediate points where there is apparently a change in the type of soil. For canal, stream and river crossings, boreholes shall be made one on either bank and one on the bed of water crossing. For railroads, state highways and national highways, at least one bore hole shall be made at each crossing location.

Minimum diameter of boring shall be 150mm. Auger boring shall be resorted to above water table, whereas below water table the boreholes shall be advanced by rotary drilling with mud circulation through all kinds of soil other than rock. While boring above water table, no water shall be introduced in boreholes. Casing shall be used to support the sides of boreholes in soft to firm soil.

The boring shall either be terminated at a depth of 5 m below NGL or on top of bed rock, if rock is encountered at a depth less than 5 m for following types of crossings:

• Highway crossings
• Railway crossings
• River or major inland water body crossing
• Location of seismic fault line and
• One each at 500m on either side of fault line crossing

For all other types of crossing location, the boring shall be either terminated at a depth of 3 m below NGL or on top of bed rock if rock is encountered at a depth of less than 3 m. Additionally, bore holes shall be made at all SV stations, IP stations and at all terminal locations.

The bore-hole samples shall be laboratory tested for the following:

1. Natural Moisture Content
2. Bulk and Dry density
3. Grain Size Analysis
4. Tri-axial shear (unconfined un-drained) test for clayey soil
5. Box shear test for granular soil

Based on the above tests, following soil data along the route shall be generated:

1. Type of soil (sand, silt, clay, etc.) up to the boring depth (i.e. 5.0 m or 3.0m)
2. Bulk and dry density of soil
3. Maximum level of water table
4. Angle of internal friction (Φ)
5. Un-drained shear strength in case of clayey soil (c)

Presentation of Survey Data

Results of soil investigation survey and laboratory test carried out shall be submitted in the form of report covering as a minimum the following.

1. Visual engineering classification of soils encountered along the pipeline route in borelog form. Depth of Ground Water Table (GWT) below NGL shall also be mentioned if encountered.
2. Soil profiles along the pipeline route shall also be prepared and attached with the report.
3. Regions along the pipeline route where hard rock is present and special excavation techniques like blasting, etc. needs to be adopted for excavation of pipeline trench shall be clearly indicated in the report.
4. Summary of results obtained from various laboratory tests and their interpretation to evaluate various soil parameters.

Visual engineering classification of soils obtained from bore holes shall be shown in Alignment sheets also, if the preparation of alignment sheets is included in SURVEYOR’s scope of work.

Location class is required to be recorded for the survey of cross-country gas pipeline as per ASME B 31.8 “Gas Transmission and Distribution Piping Systems” along with chainages at change points of each class location. Location classes along the pipeline route shall be determined as follows:

“A zone, 400 m wide (one quarter mile), shall be considered along the pipeline route with the pipeline in the centre-line of this zone. Then the entire route of the pipeline shall be divided into lengths of 1600 m (one mile) such that the individual lengths will include the maximum number of dwellings intended for human occupancy. The number of such dwellings which are intended of human occupancy within each 1600m (one mile) zone shall be counted and reported along with other survey data. Areas shall be classified based on guidelines as given below:

Location Class 1	:	Any 1600 m (one mile) section that has 10 or fewer dwellings intended for human occupancy.
Location Class 2	:	Any 1600 m (one mile) section that has more than 10 but less than 46 dwellings intended for human occupancy.
Location Class 3	:	Any 1600 m (one mile) section that has 46 or more dwellings intended for human occupancy except when a Class 4 Location prevails.
Location Class 4	:	Areas where multi-storey buildings are prevalent, and where traffic is heavy or dense and where there may be numerous other utilities underground.

In addition to the criteria indicated above, while classifying areas, additional consideration must be given to possibilities of increase in concentration of population along the pipeline route such as may be caused by the presence of schools, hospitals, recreational areas of an organized character, places of assembly, places of worship etc. If one or more of these facilities are present, the area shall be classified as a Class 3 Location. Also, due consideration shall be given to the possibility of future development of the area during the design life of the pipeline. If it appears likely that future development may cause a change in the Location Class, this shall be taken into consideration while determining its Class Location."

The objective of cadastral survey is to identify the ownership & land use details and collect data/ all other details sufficient for acquisition of RoU along the pipeline route identified by Company and duly surveyed and established on ground.

Requirements

The SURVEYOR is responsible for collecting all revenue and other maps as well as arranging all necessary forms required for carrying out cadastral survey. SURVEYOR is required to carry out plane table survey, as may be required, along the pipeline route covering an area 30 m on either side of centreline to show the following details in cadastral maps to be prepared on 1:2500 scale.

1. Pipeline alignment as per details made available.
2. RoU limit on either side of centreline as per details given in Data Sheet. RoU limit at turning points shall be marked in a curve having turning radius of 50 times pipeline outside diameter for pipeline size 18” & above. The pipeline diameter shall be indicated in data sheet. In case of multiple lines in same RoU, the largest pipe size shall be considered for this requirement.
3. Property identification/ survey number, Part on survey numbers as per the latest official revenue records.
4. Identification of RoU of existing pipelines/utilities/ rail, roads, canal, river and other pipeline crossings on the Cadastral maps.
5. Number and type of trees within RoU limits.
6. Other major features such as given below:
• All built up areas.
• Religious places, schools, hospitals etc.
• Railway lines, Highways and district / village roads.
• Creeks, rivers, canals, drains etc.
• Forest land (Reserved/Protected/Social)
• Wildlife sanctuaries
• Industrial Land.
• Quary/ mining and other prohibited areas.
• Over-head/ underground utility crossings

The above information shall be adequate in all respect for RoU acquisition and obtaining forest clearance (if any).

SURVEYOR shall also prepare a schedule, as per format to be approved by Company/ Engineer-In-Charge, showing information on part and details of ownership (for obtaining pipeline Right of Use (ROU). SURVEYOR shall prepare a summary of ownership details of land covered within 30 m on either side from the centreline of pipeline giving all relevant details village wise including land cost and crop cost supported by the relevant documents from respective District headquarters.

Presentation of Survey Data

The SURVEYOR shall submit all survey data in the form of following drawings /documents:

• Cadastral maps in scale 1:2500.
• Cadastral Survey Report including summary of ownership details, land and crop cost detail and other documents as above.
• All revenue maps collected by the SURVEYOR from various authorities.
• All forms/ performas necessary for estimation of land cost.