Coastway Subsurface Laser Scanning Article - Civil Engineering Surveyor Journal July 2009

8/4/2019 Coastway Subsurface Laser Scanning Article - Civil Engineering Surveyor Journal July 2009

http://slidepdf.com/reader/full/coastway-subsurface-laser-scanning-article-civil-engineering-surveyor-journal 1/4

CIVILENGINEERING

SURVEYORJune 2009

XCES

Mapping

The Global Funding Gap

GPR & Sub-surface Scanning

The Journal of the Institution of Civil Engineering Surveyors



Sub-surface Surveys

22 CES June 2009 www.civilengineeringsurveyor.com

HAVE you ever had the unfortunateexperience of being told by yoursenior surveyor that today’s job is to

get togged up and be prepared to loweryourself down into a sewer, in order toprovide accurate survey data for the client?

Wastewater and stormwater manholesurveys are where boys become men andno matter what excuse you make to theboss, you simply have to put on your noseclip, wear the full waterproofs (hopefullywith no leaks), check your gas detectorworks and demonstrate to the councilinspector that your confined space training

certificate is current, clip your harness tothe tripod winch-line and lower yourself down into the darkest hole imaginable.

You’re also comforted that yourtetanus inoculation jabs are up-to-dateand you have your Weil’s disease card inyour top pocket, just in case you getbitten by a furry friend and have to getchecked out at the local infirmary. Nevermind the beautiful aromas, the scurryingof various rodents, floating objects (somestill warm) and the sound of rushingwater which washes your tripod legs awaywhen you think you’ve just found decentanchor points for the spikes. Thatexpensive new total station you purchasedlast week has sunk without a tracebeneath the rippling brown waves, neverto be found again.

Not to worry, you still have your Disto,your waterproof notebook, together withChina graph pencil and state-of-the-artmicro digital camera that will capture allthe data you need in order to provide theclient with its ‘picture’ of what liesbeneath the busiest road in Dublin.

The client requires a detailed record of the existing state of the manhole andintersecting pipes which are flowing intothe supersize manhole, 3m deep, from alldirections and at all levels. Your sketch andapproximate directions of the pipes is to beaccompanied by several high resolution

digital images from the new and expensivecamera you’ve just purchased at the sametime as the departed total station. You tugon the cable and shout to your assistantabove on the surface to haul you up,because you think you’ve got enoughinformation and you just can’t handle therodents gnawing on your wellie bootsbefore the slurry enters through thedeveloping toe hole. Unfortunately, it’s asyou almost reach the surface, see the sunstreaming through the small accessmanhole cover above, when the winch jarsand the new camera jolts from your pocket

and splashes into the murky torrents below,lost forever...

Now all of the above may sound like thesurvey from hell, but this is the wayCoastway used to carry out these surveysand many survey companies still do. Thenumber of complaints were rising rapidlyand surveyors were handing in their noticerather than be subjected to sub-surfacesurveys of the nature just described. Wesimply had to come up with an alternativethat involved little or no access by asurveyor with survey equipment into themanhole chambers.

The answer was literally staring us inthe face. We could use our laser scanner(a Leica HDS Scanstation 2) to surveyroads, buildings and surface manholesduring the day to provide the surfacetopographical survey, all connected toOrdnance Survey Ireland’s National Gridwith a Leica 1200 SmartNet GPS. We

Ground penetrating radar and sub-surface

laser scanning — the full 3D picture A light-hearted view of surveying water and wastewater pipes and manhole chambers

Mark Hudson, Director, and Jeff Hott, Survey and Laser Scanning Manager, Coastway,

and Dr James Hodgson, Senior Geophysicist, Minerex Geophysics Ltd

That expensive new total station youpurchased last week has sunk without

trace beneath the rippling brownwaves, never to be found again.

3D pipes and point cloud data – Leica Cyclone software image.

A typical manhole survey today.



Sub-surface Surveys

24 CES June 2009 www.civilengineeringsurveyor.com

could then use the laser scanner for thesurvey of the manholes with the lidremoved and a ‘low’ tripod setting andscan down into the hole from above.

Our partner, geophysicists Minerex, wasintending to carry out ground penetratingradar (GPR) surveys of the same area, abusy road junction in Dun Laoghaire,

Dublin, which could only be surveyed byGPR in the middle of the night (read morelater). That survey would complete part of the ‘hidden detail’ below the ground bylocating buried utilities. However, theproblem still arose with the large manholechambers and surveyed detail required.

Jeff Hott, the survey and laser scanningmanager, pondered on the use of a laserscanner for the job, but the Scanstationwas just not suitable, we needed thescanner to be physically inside themanhole. Then in a ‘Eureka’ moment Jeff shouted out, why not use the Leica HDS6000, turn it upside down, drop it down themanhole, turn on the scanner and ‘hey

presto’ you’ve got a 3D model point cloudof the whole manhole chamber andassociated interconnecting pipework. Notonly that, but you’d get a laser scan surveyof at least 25m down each pipe, giving youthe direction of each, the quality andcondition, all at the same time.

Jeff was laughed out of the room, notleast by his director, who wasn’t willing todrop a £60,000 scanner down a black hole.There might be a chance it could producewhat was required, but it might also be lostin the murky waters, only to be found on adistant shoreline some months hence. Thinkagain his director said, but no, Jeff had avision and he knew he had seen somethingat a laser scanning conference which

caught his eye previously and just mightwork and provide the answer to the steadybut continual departure of surveyors whorefused to enter a confined space manholeever again – ‘not for all the tea in China’was muttered.

After scouring through the informationbrought back from a four-day meeting, theanswer to all the underground scanningproblems presented itself in two pictures.The inverted tripod! This tripod speciallydesigned for the HDS 6000 would solve allour problems. After receiving a healthybonus for presenting this truly remarkablesolution, Jeff and his team waited withbaited breath for their new piece of equipment to arrive.

Upon arrival the team assembled thenew kit and prepared for the initial test.After connecting the scanner to the tripodthe HDS 6000 preformed its first scanupside down with no problems. Ecstatic

and elated, the team decided that it wastime to perform their second test in a liveutility chamber. They packed theequipment and headed out to the back of an industrial estate to begin their first‘real’ manhole survey.

After a few moments the tripod was inplace, the computer at the ready and thelast thing to do was to attach the scannerto the underside of the tripod. The nextstep was to see who drew the shorteststraw and would have to attach thescanner onto the tripod over the openmanhole, some 3.5m deep. Laser scanning

surveyor Chris Byrne was about to becomehero or villain within the confines of thecompany hierarchy. With trembling handsand a sweaty brow Chris attached thescanner to the tripod successfully. Once

Jeff was laughed out of the room, not least

by his director, who wasn’t willing to drop a

£60,000 scanner down a black hole.

A 400MHz hand towed GPR unit.

Credit: Minerex.

Top: The GPR survey grid.

Above: The sub-surface utility map.

GPR sub-surface images.



25www.ices.org.uk CES June 2009

Sub-surface Surveys

attached, the utility chamber was scanned at multiple

levels and everything worked perfectly!With our confidence at its highest level and no

accidents, the next step was to perform thistechnique in a real world project. In the middle of thenight, using the HDS 6000 scanner and tripod system,we scanned three separate wastewater manholechambers below ground, in a three-hour time span inDun Laoghaire town centre. At the same time we setthe Scanstation 2 running and scanned the entirestreet scenes.

Ground penetrating radarGPR allows detailed images of the sub-surface to beseen in real time. A geophysical operator pushes or

pulls the GPR often mounted in a buggy. The baby inthis buggy allows the squiggles and wiggles to beinterpreted into pipes and cables and other sub-surface features, which can then be physically tracedacross the ground. This can all be done without theneed for excavation or dipping your head or equipmentinto dark holes.

The position of the identified services can either bemarked on the ground to be surveyed in later, andtheir position joined together — like a giant game of dot-to-dot — or the data can be processed dependingon the acquisition parameters back in the office toprovide a 3D/2D cross-section view of the servicescrossing the site.

Combining laser scan and GPRsurveysWith the scan data from both scanners back in theoffice, our modelling team was able to create a 3D sub-surface pipe network. We achieved fantastic results, asthe images in this article demonstrate.

GPR data of the same project was provided byMinerex to be combined with the laser scan surveys.Wastewater pipes were identified and extruded into 3Dobjects, all maintaining the same spatial geometry asthe surveyed scan data. The final combination of thethree surveys provided the full 3D picture we requiredand had been striving to achieve.

Existing and new clients are now able to work withan accurate and highly detailed 3D model of existingwater/wastewater pipework within the hidden world of sub-surface utilities. New pipework can be broughtinto existing manhole chambers, aware of the spatial

The next step was to see who drew

the shortest straw to attach the

scanner onto the tripod over the open

manhole, some 3.5m deep.

Sub-surface laser scanning software images.

Jeff Hott (right) and Chris Byrne with the laser scanners.

positioning of existing pipework. Reconditioning of manholechambers and connecting pipes can be analysed, programmed andmarked up for upgrade works.

All of above highlights the advances we have developed withthe inverted laser scanner for use in this highly inhospitableterritory, to provide a far superior end product to that providedpreviously. Health and safety issues are vastly improved by nothaving to send our surveyors underground and requests to leavethe company have ceased...

Mark Hudson, Director, and Jeff Hott, Survey & Laser Scanning

Manager, Coastway, and Dr James Hodgson, Senior Geophysicist,

Minerex Geophysics Ltd

w: www.coastway.net www.minerex.ie This article is derived from the presentation given at the ICES Ireland seminar held at Civilex, RDS, Dublin on 25 March 2009.

Documents

Coastway Subsurface Laser Scanning Article - Civil Engineering Surveyor Journal July 2009