Accurately mapping underground utility and telecom network assets represents a growing opportunity for professional surveyors. In order to ensure continuing improvement in the accuracy of location information about underground utilities, some international jurisdictions are requiring that new or modified underground infrastructure be surveyed by a registered surveyor. Technical advances are making it easier for surveyors to conduct underground surveys. For construction projects owners, engineers and contractors are increasingly recognizing that surveyors who can offer a combined above- and below-ground survey are able to add significantly more value than the traditional above-ground-only survey.

Technical advances enable surveyors to conduct underground surveys

Utility locating involves remote-sensing and safe excavation technologies for identifying, detecting, and labelling underground utility infrastructure including telecommunication, storm and sanitary sewers, water, electricity distribution, natural gas, cable television, fiber optics, heating and others. Underground locate practitioners use all the information that is available to them including as-builts (however unreliable), site surveys, remote sensing tools such as electromagnetic induction, ground penetrating radar, and other techniques, and potholing. Industry standard tools are electromagnetic induction and detection (EMI), which can only detect metallic objects and has limited vertical accuracy and ground penetrating radar (GPR) which can detect nonmetallic objects and provide 3D location, but is not reliable with certain soil types. Until recently interpreting GPR scans has required a trained geotechnologist, which has limited the adoption of GPR by surveyors and other potential users. Furthermore, most EMI and GPR devices are intended to operate at a walking pace making them dangerous and inefficient for large scale surveys. Recently there has been accelerating innovation in advancing technology for detecting underground infrastructure by startups and by established firms such as Leica Geosystems and Bentley. Recent advancements to the remote sensing technologies commercially available for detecting underground infrastructure are enhancements in GPR and the development of inertial locating and acoustic surveying.

Traditional output from a GPR scanner showing hyperbolas reflected from underground utilities

A major inhibitor to broader use of ground penetrating radar for detecting the location of underground utilities is the difficulty in interpreting radar scans. non-geotechnical professionals including surveyors found it a challenge to interpret GPR scans consisting of images with hyperbolas showing the reflections of RF waves from underground objects. GPR remained the preserve of highly trained geotechnical and other underground engineering professionals. In 2019 Leica Geosystems released the DSX ground penetrating radar system that is the first to address this gap in a compact, portable system. As a result of the growing interest among the surveying community to expand their professional offerings to include above- and below-ground surveys, Leica Geosystems is focusing on simplicity with its latest GPR devices and software.

Output from the DSX with DXplore software showing tomographic image of detected underground utilities

A key feature of the DSX GPR device and DXplore software is analytics to interpret the GPR scans and visualize underground infrastructure in the form of tomographic images, rather than radar hyperbolas. For accurate locating the DSX supports seamless integration of positioning sensors (GNSS antennas) and is the first device to be integrated into machine control workflow through avoidance zones based on an underground utility map generated by the DSX. In a semi-outamted process software processes captured GPR images are used to idenitfy the location of underground cables and pipe. The resulting 3D model can be exported as a 2D or 3D vector file in a CAD compatible file format.

This may not be useful for experienced GPR practitioners. Geotechnical experts are trained to work with B-scan/radargram data representation and interpretation. But for surveyors and others who don’t have GPR experience and recognize that underground surveying represents a significant business opportunity, this represents a way to incorporate underground surveys underground into their practice.

Requiring a survey crew to be on-hand throughout an excavation to survey exposed utilities can be cost prohibitive. A research project by Costain and Bentley found accurately surveyed contral points enabled photogrammetry using a consumer grade smartphone can generate a 3D model of comparable accuracy to a traditional survey and is much more cost efficient. It was shown that a simple workflow is adequate to capture enough information with a smartphone to accurately determine the location of underground utilities.

Mark ground control points (GCPs) around the area. They have to be visible in the pictures taken with the smartphone.
Take pictures from varying angles and heights around the exposed utilities with a smartphone.
Survey the GCPs with a total station, at least three are needed to accurately determine the location of the 3D model created from the pictures.
Upload the photos taken with the smartphone and process them and GCPs together to create a georeferenced 3D model of the exposed utilities.

This process has been found to result in a 3D model of comparable accuracy to traditional survey and after the control points have been surveyed it is something that anybody can do. Typically it involves taking 40-60 pictures with an ordinary smartphone. After uploading the pictures, processing them with Bentley’s ContextCapture software to create the georeferenced 3D model, the resulting 3D model can be made available to others on the construction project using an online web link that allows the 3D model to be displayed along with existing 2D utility as-builts.

To visualize the location of underground infrastructure in 3D mixed reality applications are available from many companies. A recent example that is dedicated to construction is Trimble’s SiteVision. It not only enables visualizing above and below-ground infrastructure, but also allows accurate measurement of positions and distances between objects.

Capturing accurate locations for new and modified underground infrastructure

In order to ensure continuing improvement in the accuraty of location information about underground utilities, some international jurisdictions require that new or modified underground infrastructure be surveyed by a registered surveyor.

Canada

A Professional Surveyors Canada report recommends requiring that all new underground infrastructure be surveyed and mapped in 3D with high precision and reliability and sharing basic information on the type, location and depth of underground infrastructure in a standardized form through a common, accessible system. It is also recommended that all underground infrastructure surveyed should be in a common format that can update a master map/GIS data set.

Singapore

In Singapore the standard guidelines for new installations of underground infrastructures specify that new underground assets should be surveyed by a registered surveyor using total station, RTK or laser scanning devices. There are special provisions for using inertial locating for assets installed by trenchless digging.

In August 2017 the Singapore Land Authority (SLA) released a standard and specifications for the procedure and practice of utility surveying in Singapore. The Standard and Specifications for Utility Survey in Singapore has progressively been included in contractual agreements for all newly built utilities by utility regulatory authorities. The standard is for open trench cases only. It covers the surveying technologies to be employed, the data to be captured, and specifies that a qualified professional (a Registered Surveyor at the Land Surveyors Board of Singapore) is required.

The standard specifies the data that should be captured for new underground utilities including telecommunication, sewerage, water supply, electric power, gas, and drainage. It specifies that after installing utilities and prior to filling the trenches an as-built survey should be performed by a registered surveyor to capture the location of the utilities with horizontal accuracy of ±100mm and vertical accuracy of ±100mm. It specifies that the survey equipment to be used should be a total station, GNSS Real Time Kinematic (RTK), or 3D Laser Scanning.

This standard is not mandated by the Singapore Government but is intended to provide a baseline to be incorporated in construction contracts. Since 85% of land is owned by the Singapore government, if a major government agency such as the Urban Redevelopment Authority (URA) routinely incorporated this standard in its contracts as part of standard procurement practice, it would effectively become a de facto mandate.

In addition to location, the standard also defines the attribute information to be captured. For example, for an electric power cable, the standard specifies that x,y,z should be surveyed at 20 meter intervals for a straight line cable and more frequently for a curving cable. In addition, height, width, number of columns, number of rows, number of ducts, number of cables and quality level should also be captured. The quality standard used in Singapore is; 1) ±100mm, 2) ±300mm, 3) ±500mm, 4) Unknown accuracy and 5) Trenchless method. In Singapore most underground utility work is open trench, although there is some trenchless which requires gyro surveying.

The standard does not specify format or what is to be done with the as-built information. Currently in Singapore there is nothing in place to require sharing of information about the underground like Netherland’s BRO or the British National Underground Asset Registry (NUAR) project. But there is a Digital Underground project underway to create an ecosystem for a digital twin of the underground as part of the Mapping Singapore in 3D project. The digital underground project was initiated by the Singapore Land Authority with the support of the Urban Redevelopment Authority. The standard for underground utility surveying would create a basic data model for sharing information about underground utilities.

France

In France, contractors are required to survey all new and changed underground structures. These surveys must satisfy certain conditions. Location coordinates of structures in an open trench must be surveyed by a certified surveyor. If remote detection technology such as GPR is employed, the firm performing this work is not required to be certified, but a certified surveyor must be involved in georeferencing the data. Whatever the method of measurement used , direct or remote, the accuracy of the locations of new or changed structures reported by the contractor must be accuracy class A, in other words 40 cm or better. For each structure the data recorded must include the name of the project manager of the site, the name of the company that provided the location information, the name of the certified surveyor responsible for determining the location of each structure, the maximum measurement uncertainty (for x, y, and z ), and in the case of remote detection such as GPR or EMI, the type of measurement technology used.

Bern

Bern, Switzerland has instituted regulations to ensure that accurate data is captured for new construction projects involving underground infrastructure. For example, there is a 24 hour rule that requires a contractor to notify the city survey department 24 hours before closing a trench. For large projects city surveyors periodically verify surveys of underground works.

Calgary, Alberta

The City of Calgary has legislated a by-law that is designed to share information about underground utilities and improve the quality of this information. The by-law requires all network operators with underground infrastructure under public rights-of-way to submit to the city electronic as-builts showing the location of newly installed network equipment. The bylaw requires that each network operator submit digital as-built drawings to the City within 60 calendar days following completion of installation of its equipment on a public right-of-way. The as-builts are required to comply with two key provisions

The equipment is less than 35 centimeters horizontally and vertically from the centre line approved in the utility alignment permit
It adheres to the CSA S250 quality standard.

Furthermore, the City reserves the right to carry out on-site inspections to verify submitted as-builts the cost of which is shared between the network operator and the City.

Conclusion

In order to ensure continuing improvement in the accuraty of location information about underground utilities, international jurisdictions are requiring that new or modified underground infrastructure be surveyed by a registered surveyor. Technical advances are making it easier for surveyors to conduct underground surveys. For construction projects owners, engineers, and contractors are increasingly recognizing that surveyors who can offer a combined above- and below-ground survey are able to add significantly more value than the traditional above-ground-only survey. Surveyors who offer combined above and below ground surveys are finding that a combined offering increases their profit margins.

This information was first published on https://geospatial.blogs.com/geospatial/2020/04/opportunities-for-surveyors-in-underground-locating-and-mapping.html