July 2018

Best practice for carrying out 3D surveys and detailed inspections of manhole chambers with no man-access requirement.

The 3D documentation of deep drainage chambers presents survey teams with a number of logistical and health and safety challenges. These challenges are primarily linked with a historic requirement for confined space ‘man-entry’ to carry out such surveys.

1st Horizon inverted 3D Laser Scan

Use of Inverted 3D scanning technique.


Confined space entry is fraught with HSE issues and considerations; such as the potential for noxious fumes, reduced oxygen levels, risk of fire and problematic escape in the event of an emergency. Specially trained staff are required with emergency escape equipment and preventative safety measures to carry out confined space survey works.

The large number of considerations and safety measures required also makes these projects risky, laborious and very costly.

The ideal scenario therefore, (as a safety conscious contractor) is to completely eliminate the need for man-access, by utilising an inverted tripod and lightweight 3D laser scanner to capture the geometry and condition of the manhole chamber. The primary benefit of utilising this technique is to vastly reduce health and safety risk.

Risk is further mitigated because the job becomes a safe, one-man operation rather than a three or four-man operation needed for a ‘Safe System of Work’ under confined space conditions where man-access is required.

1st Horizon inverted 3D Laser Scan

Inverted tripod ready to deploy the 3D scanner into the chamber.

There are also significant cost savings for clients due to a much quicker capture time, less staff needed and minimal health and safety preparations as well as a reduction in required preventative measures.


The 3D laser scanner is first attached to the head of the inverted tripod. The tripod then forms a stable platform from which multiple telescopic attachments can be utilised to lower the scanner into the chamber in a carefully controlled manner. The scanner head can comfortably reach depths of up to 4.5 metres below the surface, with the device being operated remotely by the surveyor.

1st Horizon inverted 3D Laser Scan

Smartphone emulator used to control the 3D scanner remotely.

The surveyor utilises a software emulator installed on their smartphone or tablet device to control the 3D scanner remotely, exactly as they would if operating the scanner manually. The scanner connects through wireless LAN, ensuring that no man-access at all is required for the survey process.

To gain accurate positioning of the subsurface geometry in the chamber, a combination of scan targets and ‘cloud to cloud’ registration can be used to accurately relate all data captured to a common reference network. The scan data can also be linked to above ground survey control stations and other surveys such as terrestrial 3D laser scanning or 3D topographic surveys. A true appreciation of not only the underground geometry, but also its relative position and surrounding context can therefore be understood.

Where further investigation into the condition of the connecting drainage pipes is required a collaboration can be undertaken with specialist CCTV crews to perform digital inspection of the drainage runs between chambers where required.


An accurate and detailed representation of the chamber is documented by the 3D laser scanner, and 3D pointclouds are produced. Pointclouds from each individual scan are linked together to form a single unified pointcloud comprising of several scans taken at different depths within the chamber.

1st Horizon inverted 3D Laser Scan

360-degree image view from the 3D scanner within the chamber.

360-degree scan images are also produced and can be used for both general visualisation and understanding, or much more detailed inspections and analysis observing dimensions, damage, defects and any other potential issues.

The scan data can be used to produce CAD & BIM model information, this information greatly assists designers and contractors when planning remedial works.

Outputs include 2D CAD sections (which can be useful for verticality checks), 3D CAD Models and Revit Models.

1st Horizon inverted 3D Laser Scan

The end result is that clients receive a much more useful package of data offering a far greater appreciation of the chamber proportions and conditions than with conventional ‘man-access’ survey methods. This provides customers with a detailed understanding of drainage chambers, whilst at the same time eradicating the need for man-access and achieving a vast reduction in health and safety risk.

This very same ‘inverted scanning’ technique can be employed for many other similar applications such as the 3D documentation of underground storage tanks, shafts, silos, towers, caverns and sink holes.

1ST HORIZON specialise in 3D Laser Scanning solutions delivered by our highly experienced surveyors. Our extensive experience includes remote, non-contact measurement and projects where access is challenging. Find out more about 1ST HORIZON’s 3D laser scanning capability today.

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