Six precautions when surveying around underground buried objects with a total station

When surveying around underground utilities, it is necessary to proceed carefully, considering not only the operational accuracy of the total station itself but also site conditions, safety checks, cross-checking with existing records, and coordination with excavation activities. Underground utilities such as water pipes, gas pipes, power lines, communication cables, and drainage pipes do not always exactly match their positions on drawings. Past construction history, delays in updating drawings, on-site modifications, temporary piping, and lack of depth information can all result in utilities being located closer than expected.

The total station, an optical surveying instrument that measures distances and angles to determine the positional relationships of points on the ground and target surfaces, is not a device for directly locating objects underground. Therefore, when using it around buried utilities, it is important to carefully read visible ground reference points, manholes, valve chambers, inspection chambers, marker stakes, pavement markings, and structural interfaces, and to take measurements while cross-checking with drawings and on-site information. This article explains six points that field practitioners should pay attention to when surveying around buried utilities with a total station.

Table of Contents

• Do not rely solely on drawings to determine the locations of underground buried objects.

• Determine survey points and instrument points with priority given to work safety.

• Carefully measure the clues visible on the ground.

• Check the distance to excavation and test-pitting operations

• Record survey data in a way that makes its intended use clear.

• Share information with stakeholders before and after surveying.

• Protect safety across the entire site without relying solely on total stations.

• Summary

Do not rely on drawings alone to determine the location of underground buried objects

When surveying around underground buried objects with an optical total station, the first thing to be careful about is not to treat drawing information as the exact actual positions. Management maps, as-built drawings, occupancy drawings, equipment drawings, and past construction drawings are all very important documents, but the lines shown on the drawings do not necessarily fully represent the actual buried locations in the field. In particular, on old roads, sites that have been renovated multiple times, places where equipment was added after residential land development, or locations where temporary installations were converted to permanent ones, discrepancies can occur between the drawings and the actual site conditions.

When measuring around underground buried objects with a total station, you may need to transfer the buried lines shown on drawings to the field. In this case, it is dangerous to assume that those lines can be treated as definitive no‑dig or safety zones just because coordinates are available. It is important to check the drawing’s creation date, coordinate system, reference points, scale, stated units, and revision history, and to confirm with the manager or construction personnel as needed. If the drawings were digitized from paper, they may include distortions from scanning or errors introduced during digitization.

Also, in drawings of underground buried utilities, even when the plan position is depicted, depth, pipe diameter, material, presence of protective conduits, and details of bends may not be sufficiently described. Even if there appears to be clearance on the plan view, they may be close in the longitudinal direction or due to gradients. A total station can measure points on the ground but cannot directly determine underground depths. Therefore, do not judge safety based on plan position alone; when necessary, consider depth information, trial excavation results, and survey/investigation results together.

On site, before re-establishing the positions of buried utilities with an electronic total station, confirm nearby manholes, handholes, valves, fire hydrants, wastewater access chambers, stormwater access chambers, ditches, utility poles, service connection points, and meter locations. These provide clues for estimating the routes of underground utilities. If the lines on the drawings are unusually offset from the actual arrangement of structures on site, determine the cause before proceeding with surveying work. The appropriate response depends on whether it is a simple drawing error, a coordinate transformation problem, or a past relocation that has not been reflected.

Even if an optical surveying instrument has high measurement accuracy, if the reference information entered is incorrect, the reported position will also deviate from reality. Around underground buried objects, there are many situations where the consistency between the baseline documents and on-site verification is more important than the instrument's accuracy. The more detailed the measured values appear, the easier it is to trust the numbers alone; however, with underground buried objects it is important to distinguish between the "measured position" and the "actual position" where they are located.

In practice, we take a conservative view of hazard zones by combining the drawing location, on-site fixtures that can be verified, past construction records, interviews with stakeholders, and exploratory investigations or trial excavations as needed. Positioning with a total station is a means to support that judgment. When surveying, do not measure solely to lay lines on the drawings accurately; measure with the awareness that the purpose is to clarify the area where work can be carried out safely on site.

Determine survey points and instrument points with work safety as a priority

Around underground buried utilities, attention must be paid to the placement of total station instrument points and survey points. In ordinary surveying, priority tends to be given to locations with good line of sight that allow efficient measurement of many points. However, near underground buried utilities it is important to avoid interference with workers, heavy equipment, excavation areas, temporary materials, and traffic flows. Poor instrument-point placement can cause the instrument to intrude into the work zone during surveying, get too close to excavation areas, or fall within the turning radius of passing vehicles and heavy machinery.

When installing a total station, the basic rule is to place it on stable ground. Around underground utilities there are locations that are less stable underfoot than they appear, such as pavement cut lines, freshly backfilled ground, temporarily restored road surfaces, alongside gutters, and around manholes. Even if the tripod seems stable when set up, nearby operation of heavy equipment or passing vehicles can cause slight vibrations that may shift the instrument. Near underground utilities, prioritize being able to set the instrument stably over being close to the survey target.

When selecting an instrument station, check not only the line of sight but also how easily personnel can move to safety. When working on roads or internal passageways, there must be enough room for workers to move safely when vehicles approach. If you place the instrument close to the planned excavation area, you may need to relocate it if the work area later expands. More relocations increase the number of times the instrument station must be set up and backsight checks performed, which can lead to coordinate mix-ups or missed verifications. If measurements can be taken from a slightly more distant, safer location, that will ultimately lead to more stable operations.

Regarding survey points, there is no need to force them directly over the presumed location of an underground buried object or at the edge of an excavation. If the purpose of the work is to check the surrounding area of the buried object, you can take offsets from safe points nearby instead of entering the hazardous area directly. For example, establish safe survey points on both sides of the presumed alignment of the buried object and confirm distances from those points to understand the relationship with the work area. Ensuring that survey personnel do not stand in hazardous locations is as important as measurement accuracy.

When using a mirror, carefully determine the position of the worker holding the mirror. In areas where underground buried objects that are not visible from the surface exist, avoid actions such as driving stakes, hammering nails, or inserting pins deeply. Even when marking is necessary, follow site rules and choose methods that are unlikely to damage buried objects. In total station surveying work, there is a tendency to focus on leaving points, but around underground buried objects the way points are left can itself become a risk.

Once instrument points and survey points are decided, share them on site before starting work. Confirm who will stand where, which areas are off-limits, whether the work will be carried out concurrently with heavy equipment operations, and whether guides or observers are needed. Although measurements with an optical total station may seem to finish quickly, you will remain at the location for a certain period when sighting, recording, re-measuring, and checking are included. Around underground utilities, site conditions can change during surveying, so it is important to set instrument and survey points with a safety margin.

Carefully measure the visible clues on the ground

Because underground utilities cannot be seen directly, when surveying the surroundings with a total station it is important to carefully record visible surface clues. Manholes, inspection chambers, valve boxes, handholes, marker posts, marker plates, road markings, service pipe risers, equipment panels, and interfaces with exterior structures all provide important information for inferring underground routes and the extent of management. These should not be treated merely as surrounding structures but recorded as survey points that can explain their relationship to the buried utilities.

How point names are assigned is extremely important when measuring with a total station. For example, if you simply record "Point 1" and "Point 2", it will be difficult to tell what those points were measuring when you look back later. Assigning point names that indicate their purpose—such as manhole center, inspection-chamber corner, valve box center, marker-stake location, pavement marking edge, planned excavation line, and corner of an existing structure—makes it easier to cross-check in later processes. Even if things are clear on site, their meaning can be lost when you return to the office to produce drawings or hand the work over to another person.

Around underground buried utilities, it is important not only to measure the center point but also points that convey shape and orientation. For manholes, measuring not only the center but also points that indicate the cover’s orientation and its relationship to the surrounding pavement makes it easier to later reconcile field measurements with drawings. For rectangular structures such as inspection chambers or valve chambers, measuring multiple corner points reveals position and orientation. If a buried utility may run at an angle relative to a road or building, capturing multiple points of the related aboveground structures makes it easier to improve the estimation accuracy.

However, aboveground structures visible on the surface do not necessarily indicate the exact centerline of underground buried utilities. The center of a manhole may not coincide with the center of a pipe, and a pipe may bend and connect away from the location of an inspection chamber. Marker stakes and pavement markings are also reference aids used during construction or for management, and they may differ from the actual buried locations. Therefore, even if you measure aboveground cues with a total station, it is important not to treat those measurements as the definitive positions of the underground buried utilities.

When measuring above-ground clues, coordinating with photographs and notes is also effective. Measurement data from an electronic total station alone may not convey the on-site conditions or visual relationships well. If you record point names and photo numbers, measurement times, the surveyor, and the purpose of the measurement, it becomes easier to make judgments when reviewing later. In particular, around underground buried utilities, the measured points may serve as the basis for safety verification. If you intend to use them as evidence, you need to be able to explain which points were measured and for what purpose.

Also, inspect the condition of the roadway and ground surface. Pavement joints, repair marks, settlement, cracks, color differences, and the extent of temporary restorations may be traces of past excavations or buried installations. Of course, you cannot determine the location of buried objects from these alone, but when combined with drawings and information gathered from interviews they become important clues. It is important not only to measure positions with a total station but also to observe site conditions and select the necessary points to measure.

Confirm the distance from drilling and trial excavation operations

Surveying around underground buried utilities may be carried out in close proximity to operations such as excavation, test digging, pavement cutting, pile driving, foundation work, and exterior construction. In such situations, the purpose is not simply to determine positions with an optical total station, but to confirm—on the safe side—the relationship between the work area and the underground buried utilities. Therefore, survey personnel need to understand how the measured points will be used in the excavation work.

When measuring planned excavation lines or work areas, confirm how far they are from the estimated locations of underground buried objects. However, the concept of separation distances changes depending on site conditions, the type of buried object, instructions from the owner or manager, construction methods, depth, soil conditions, the type of heavy equipment, and so on. You should avoid judging "this much distance is sufficient" based only on a general sense. The distance measured by a total station is, at best, a planar distance and cannot, by itself, determine underground depth or oblique proximity.

Care must also be taken when staking out test excavation locations. Test excavations may be carried out to verify the positions of underground buried objects, but the excavation itself is an operation that approaches those buried objects. When staking out a test excavation location with an optical total station, check the buried lines on the drawings, surface clues, the workers' positions, and the excavation method, and avoid driving stakes or nails directly into hazardous locations. If necessary, consider establishing points outside the test excavation area or on a safe reference line and confirming positions by measuring dimensions from those points.

When indicating excavation areas with an optical total station, it is important to clarify the meaning of the measurement points. If it is unclear whether a point represents the excavation center, the excavation edge, the estimated center of an underground utility, or a reference point for safety checks, it can lead to misinterpretation on site. In particular, on sites that use multiple types of colored markings or stakes, survey points and construction points can easily be confused. Survey personnel should confirm point names, the meaning of markings, and how they will be displayed on site with all relevant parties.

When conducting surveys during excavation, be aware that the ground and structures may change. As excavation progresses, survey marks may be lost, lines of sight may change, and the area visible from instrument stations may be altered. If you need to check elevations and positions before and after backfilling, it is important to decide in advance when and what to measure. When measuring at the stage where buried objects are exposed, prioritize worker safety, preventing collapse, and restricting access, and avoid approaching too closely to take measurements.

A total station can measure points at a distance using a prism (mirror) or reflectorless measurements. However, with reflectorless measurements, readings can be unstable depending on the condition, angle, material, wetness, dirt, or sunlight on the reflecting surface. When measuring exposed pipes or structures around underground buried utilities, confirm which surface is being measured, whether the reflection point has shifted, and whether multiple measurements produce stable values. It is important not to adopt the measured numbers as-is but to verify their validity against the site conditions.

Record survey data in a way that makes its intended use clear

Survey data around underground buried utilities may later be used for construction decisions and safety checks. Therefore, data obtained with a total station should be recorded not merely as coordinate values but in a way that makes their purpose clear. If it is not clear which points relate to existing buried utilities, which points mark the excavation area, which points are reference points, and which points have been verified, the data will be difficult to use in practice even if measurement accuracy is high.

First, clarify the job names and data names. Around underground buried objects, multiple surveys such as road centerline, boundaries, structures, as-built measurements, and buried-object verification may be conducted in parallel within the same site. If data names are ambiguous, it becomes unclear which operation the data belong to, creating a risk of staking out positions using the wrong coordinate list. Using names that clearly indicate the date, location, task, and measurement purpose will make later organization easier.

Rules for point naming are also important. For points related to underground buried utilities, make their type and meaning clear. For example, assign consistent names, in accordance with site rules, for manholes, valves, inspection chambers, marker positions, estimated buried lines, planned excavation edges, trial excavation locations, verification points, escape points, and so on. If abbreviations are used, ensure that the parties involved can understand them. Point names that only the surveying staff understand tend to cause misunderstandings during handover.

Careful attention is required when handling elevations. Around underground buried utilities, not only plan position but elevation information such as ground surface elevation, pavement surface elevation, manhole top, pipe invert, and excavation bottom can be important. However, if it is not made clear what kind of elevation was measured with the total station, it may be used incorrectly later. Check mirror height, instrument height, reference height, temporary benchmark, elevation datum, and local height, and clearly specify the reference when handling elevation data.

Recording the coordinate system and reference points is also essential. Whether the management drawings for underground buried utilities were created in a public coordinate system, a site-specific coordinate system, or are managed using local construction coordinates affects how measurement data are handled. Mixing data with different coordinate systems can cause large positional discrepancies. Before measuring with a total station, verify the instrument station, backsight point, known points, and the source of the coordinate list, and after measuring you must also keep a record of which reference system the data were acquired in.

Recording the conditions at the time of measurement is also useful. Weather, line of sight, presence of nearby work activities, condition of the measured object, reflection conditions, measurement method, whether re-measurement was performed, and similar details serve as material for later judging the reliability of the measurement values. For example, information such as the road surface being wet due to rain, being unable to approach the survey point because of traffic controls, measuring from a long distance using a non-prism, or the ground changing due to excavation cannot be determined from coordinate values alone. Around underground buried objects, it is important to record not only the numerical accuracy but also the circumstances under which the numbers were obtained.

Be careful when outputting or sharing data. When transferring data extracted from surveying instruments to drawings or tables, check that point names, coordinate values, elevations, and remarks have not shifted. In the process of deleting unnecessary points, changing point names, or reordering coordinates, the meaning can be altered. Points related to underground buried objects can lead to safety problems if misused, so it is desirable to reconcile the final data with the original data and keep a record of any changes.

Share information with stakeholders before and after surveying

When surveying around underground buried utilities, it is important that surveyors do not make decisions on their own. Depending on the type of buried utility and the scope of its management, many stakeholders may be involved, such as facility managers, the main contractor’s representative, construction managers, heavy-equipment operators, excavation workers, guidance personnel, and those responsible for nearby works. Before measuring with a total station, share the survey purpose, the target area, no-entry zones, work procedures, and the buried-utility information that needs to be confirmed to reduce misunderstandings on site.

In pre-survey meetings, we decide which drawings will be treated as the authoritative ones, what area to survey, which points to mark on site, and who will verify the measurement results. Information about underground buried objects may be split across multiple documents. When old drawings, new drawings, as-built drawings, management drawings, and field notes are mixed together, different personnel may be looking at different information. Before determining positions with a total station, it is important to assemble the materials to be used.

When taking measurements on site, confirm the meaning of each survey point there and then. Even if the surveyor intends to say "this is the estimated location of the buried object," it is dangerous if the construction team interprets it as "this is the line up to which you may excavate." Estimated location, verified location, reference location, construction location, and safety boundary each have different meanings. Around buried objects, differences in wording directly translate into work risks, so make the terminology used on site clear.

Sharing information after surveying is also important. Rather than simply handing over the acquired coordinates and drawings, convey the assumptions under which the measurements were taken, which points have been confirmed on site, which points were reconstructed from drawings, and where uncertainties remain. Data from total stations can appear as precise numbers, causing recipients to misconstrue them as definitive information. If there is uncertainty about the location of underground buried objects, make that clear.

When coordinating with heavy machinery or excavation operations, confirm how the survey results will be used on site. Whether survey points will be used as references to determine excavation locations, to define the extent of test excavations, or to set the positions of temporary enclosures and protective materials will affect the required accuracy and the way the information is presented. It is important that all stakeholders share the same understanding so the meaning of the points does not become unclear after the surveyor has left the site.

Also, in areas around buried underground utilities, new information may be discovered on site. If trial excavations reveal a pipe located differently from the drawings, an old pipe remains, there is piping not shown on the drawings, or an unknown structure is found under the pavement, these findings must be reflected in the survey data. Do not treat the initially measured data as fixed information; be prepared to update it based on on-site verification. When updates are made, manage the data to ensure that old and new data do not become mixed.

When sharing information, it is important not to rely solely on verbal communication. Verbal explanations can be conveyed quickly, but they are difficult to verify later and are easily lost when the person in charge changes. Combining survey maps, point-name lists, site photographs, brief notes, and work records makes it easier to make judgments in later stages. Because surveying around underground buried objects is also part of safety verification, it is important to share it in a form that remains as a record.

Protect safety across the entire site without relying solely on total stations

A total station is an effective instrument for understanding positional relationships around underground utilities, but it alone does not ensure safety. A total station can basically measure points on the ground or target surfaces that can be sighted. It does not directly confirm the actual positions, depths, bends, branches, or the condition of protective materials of pipes and cables hidden underground. Around underground utilities, it is necessary not to overtrust survey results and to combine them with comprehensive on‑site safety checks.

First, surveying with an optical total station is a means of estimating the positions of underground buried facilities, laying out drawing information on site, and organizing the relationship with the work area. To make a final determination about the presence or absence of buried facilities, it is necessary to integrate multiple sources of information such as owner/manager information, on-site markings, surveys, trial excavations, construction history, and confirmation with relevant parties. Even if the survey measurements are accurate, if the underlying drawings are outdated or the underground route has changed, there is a risk of overlooking hazards.

During measurement work with a total station, focusing too much on sighting can reduce awareness of the surroundings. Around underground buried utilities, heavy machinery, vehicles, pedestrians, materials, openings, steps or uneven ground, temporary piping, traffic control devices, and the like are often nearby, so it is also important for the surveyor to ensure their own safety. While looking through the instrument or aligning the mirror, it becomes difficult to notice movement around you. When necessary, assign a person to watch over the work and clearly define the areas where entry is permitted during surveying.

When performing surveying and excavation work at the same time, it is also important to decide the priority of the tasks. Forcing measurements close to operating excavation machinery not only compromises the surveyor’s safety but can also make readings unstable due to machine vibrations. Decide in advance whether to pause heavy equipment to take measurements, measure from a distance, or separate the working times. Even if it would only take a short time, avoid inserting surveying at a dangerous moment.

Care should be taken when handling markings and stakes around buried utilities. Marks may be placed on the ground to clearly indicate positions, but if the meaning of a mark is misunderstood it can be dangerous. Also, any items driven into the ground must be carefully evaluated to ensure they cannot damage buried utilities. In locations where the proximity of buried utilities is suspected, avoid marking methods that require deep driving and choose safe methods that comply with site rules. Colors, symbols, and lettering used for markings should also be standardized so that all relevant personnel can understand them.

Don't forget that site conditions can change after surveying. Temporary structures may have moved, pavement may have been cut, excavation extents changed, backfilling progressed, road markings erased by rain, or work crews changed; on-site conditions at the time of surveying and at the time of construction can differ. Around underground utilities, be aware of how long the information obtained at the time of surveying remains valid, and if conditions change, reconfirm. In particular, if markings have disappeared or reference points have shifted, do not reconstruct past points by guesswork—re-measure as necessary.

Total stations enable efficient surveying, but when working around underground utilities it is important not to prioritize efficiency alone. If you cut corners on safety checks, document verification, sharing with stakeholders, measurement records, and rechecks, it can lead to major rework or accidents later. Surveyors are not merely people who measure points; they are responsible for organizing on-site positional information and supporting safe construction decisions. By maintaining that awareness, the measurements from a total station can be made more useful in practice.

Summary

When surveying around underground buried objects with a total station, confirming preliminary information and taking safety precautions is even more important than in ordinary positional surveys. Because underground buried objects are not directly visible from the surface, it is necessary to combine drawings, on-site clues, information from relevant parties, and, when necessary, investigation or trial excavation results to make a judgment. Even if the total station displays detailed numeric values, that alone does not confirm the actual position of the underground buried object.

In practice, what's important is not to rely solely on drawings but to carefully verify on-site features such as manholes, inspection chambers, valves, markings, and traces of pavement restoration. Instrument and survey points should be chosen not only for sight lines and efficiency but also with consideration for worker safety, clearance from heavy equipment, stable footing, and ease of evacuation. When working close to excavations or trial pits, it is essential to clarify the meaning of survey points and avoid confusing estimated positions, construction positions, and reference points used for safety checks.

Also, surveying data must be organized so that their purpose is clear when reviewed later. By retaining point names, the coordinate system, the vertical datum, measurement conditions, and associations with photos and notes, the data will be easier to use for construction management and handovers. Because survey results around underground buried objects can be related to safety assessments, it is important not to share them with ambiguous point names or unknown reference datums.

Sharing information with stakeholders is also a key point. Before surveying, confirm the documents to be used, the area to be measured, the meaning of the points, and the work procedures; after surveying, communicate the assumptions behind the measurement results and their uncertainties. If new information is discovered on site, update the survey data and manage it so that it does not get mixed with old information. Around underground buried utilities, surveyors, construction managers, workers, and facility managers having the same understanding leads to safer work.

Total stations are effective instruments for organizing the positional relationships around underground buried objects. However, because they are not devices that directly confirm subsurface conditions, it is necessary not to overtrust the survey results and to use them in combination with on-site verification. By planning survey points with a margin for safety, keeping careful records, and sharing information clearly, you can reduce rework during excavation and construction and help lower the risk of contacting underground buried objects.

If you want to further streamline on-site position verification and record-keeping, it is effective to combine total station survey results with a digital recording environment and data management methods that are easy to use in the field. By clearly preserving measured positions, managing them together with photos and notes, and making them easy to share with stakeholders, the process of checking around underground buried utilities becomes safer and more reliable. Rather than relying solely on specific equipment or services, choose methods that suit site conditions, company rules, and the instructions of clients or managers, and link survey results to safe construction decisions.