Monday, 26 November 2018

Advantages of Terrestrial Laser Scanning (TLS) Method for Train Tunnel

Recently JPSurveys utilised 3D Terrestrial Laser Scanning method to precisely determine the 3D as-built alignment of the existing LRT tunnels in order to facilitate design and construction work above the tunnel
Left: scanning work at the site; Right: 3D virtual point cloud created  

As the tunnels (3 stretches; few hundred meters each) are relatively short in length, the traditional, competitively-priced 'total station method’ could also be feasible. However, for this method to work, the exact locations of the required cross sections (initially estimated at 9 nos) needed to be specifically identified and confirmed before the start of field survey work.

Eventually, two options were proposed to our client for consideration: total station method (option A), or TLS method (option B). We are pleased with our client's farsightedness in choosing Option B albeit a costlier option. It was the right choice as changes were indeed made after completion of the field survey work: the final locations of the required 9 cross sections have since been altered and additional sections were also requested by the engineer/planner

If the client had chosen option A, it would have meant remobilizing our team for the second time to pick up those cross-sections. Thus, the advantage of TLS method enabled the entire tunnel to be captured as one continuous 3D model; thereby allowing an infinite number of detailed cross-sections to be extracted without the need to re-survey the site - significantly saving costs, eventually.

Precious time lost is also averted: the working time allowed in such a busy train tunnel is typically limited to a few hours past midnight i.e. between the running of the last train for the night and the start of the first train in early morning hours. This is compounded by the time-consuming process required to obtain permission and securing safety escort from the train operator or authority to resurvey the tunnel the second time.
Extraction of 2D cross sections from the rich and accurate 3D model

Tunnel 3D position (lower right)  is accurately determined  to validate  the  design and construction work on top of the tunnel

JPSurveys provides 3D laser scanning survey services for various applications; Kindly contact us

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