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HMJV chooses GSaaS for subsidence monitoring

Identifying impact on road surface condition due to major tunnelling project 

“Access to highly accurate LiDAR data and high resolution ground-level imagery to identify road defects and features”  

Backround

National Grid is constructing a 32.5km tunnel across South London to house electricity transmission cables up to 60 meters underground. The project was developed to minimise disruption by eliminating the need to dig up existing 50 year old cable infrastructure reaching end of life.

Hochtief-Murphy Joint Venture (HMJV) was awarded the contract to deliver the tunnelling and shaft work of the second phase of the London Power Tunnels (LPT) project. They approached Getmapping to survey specific sections of the affected A2 and identify / analyse any changes to the condition of the road surface, during and post tunnelling works.

The Solution

The solution consists of three Mobile Mapping surveys of two separate sections of the A2:

  • an initial survey of all six lanes as a baseline / pre-condition survey
  • a survey during tunnelling works
  • a post-condition survey once tunnelling works underneath the A2 are complete.

The surveys provide highly accurate LiDAR data and high resolution ground level imagery, captured using Getmapping’s Leica Pegasus Two: Ultimate system and pavement camera, with targeted image capture along the road to identify any road defects such as potholes or cracks.

Getmapping processed the data and extracted the road features from the point clouds.

“Looking for a reliable pre-and post condition monitoring for the busy A2 stretch we are undertunnelling, LiDar methodology from a vehicle was chosen. The data delivers a detailed record of the existing road and of all changes caused by the tunnelling underneath.”

Christian Eidner, HMJV Survey and Monitoring Dept.  

Conclusions

The frequency of the survey data enables HMJV to run pre-condition, during and post-condition verification analysis, primarily on the road surface. The Mobile Mapping solution is:  

  • Highly accurate: Data was delivered to 5mm absolute accuracy with additional ground control
  • Cost-effective: The solution was quicker and more cost-effective than traditional topographical survey techniques. Getmapping ensured specific, structured mechanisms were in place to ensure ‘right first time’ data collection
  • Fast:  Data capture was up to ten times faster than a traditional topographical survey (source: Leica)
  • Non-disruptive: No traffic management or road closures were required 
  • Safe: Capture was from the safety of a moving vehicle, minimising risk to drivers and surveyors 

HMJV_subsidence_monitoring.pdf contains the full story in printable format.

To find our more about how we can help with subsidence monitoring, please call us now on 01252 849440.

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