The PANDOSCOPE is a coupling of the PANDA Instrumented Dynamic Cone Penetrometer (DCP) (tip resistance vs depth profile) and Geoendoscopy (down the hole imagery).
For rail applications, the PANDOSCOPE is used as a non-destructive rail track ballast and formation condition assessment method when planning track maintenance and renewal.
Other PANDOSCOPY applications include tunnels and underground space condition assessment, pavement works platforms and concrete segregation.
Here are some of the research papers on the PANDOSCOPE technology applications.
In rail applications, the PANDOSCOPE measures geotechnical and geophysical aspects of the track bed and provides pseudo-continuous track monitoring with the following outcomes:
- Layer characterisation for ballast and formation (identification, thickness, water content (qualitative), estimation of the soil grain size distribution and ballast condition (ballast fouling) assessment)
- Mechanical information: cone resistance (direct measurement) or CBR or other parameters with correlations
PANDOSCOPY is typically done by rail asset managers / infrastructure managers on the existing rail track network with a view to prioritising and allocating rehabilitation efforts and funding only to the sections that require priority attention whilst minimizing track downtime. This is to maintain the current usage requirements or accommodate increases in safety, train frequency, speed and load. The PANDOSCOPE data helps them optimise the track maintenance and track renewal strategy. Sometimes, PANDOSCOPE testing is combined with network Ground Penetrating Radar (GPR) data to provide more information in problem areas.
The PANDOSCOPE also provides engineering services with reliable geotechnical data for track design purposes. The knowledge of mechanical and physical properties of existing formation (subgrade and sub ballast layers) is very important for the future track design.
The PANDOSCOPE overcomes the limitations of the majority of classical geotechnical tests (drilling rigs, pot holing). Benefits include:
- Proven approach
- Tried and tested investigation strategy for track maintenance and renewal (localised or cross network)
- Stand alone PANDOSCOPY or the coupled use of PANDOSCOPY and GPR
- Several thousand kilometres of investigations – over 50,000 tests
- Passenger and heavy haul freight networks
- Several countries including France (SNCF), Belgium, USA, Canada, Singapore and Australia
- No destabilisation / disturbance of the track
- Important if renewal works are delayed or do not proceed
- Better informed decision making
- Speed and versatility
- Limited track possession time required (e.g. can test between trains working under lookout protection)
- Light weight portable equipment enables track access onto embankments and into cuttings
- Testing not limited by the height of equipment e.g. due to overhead electrification
- Cost effective methodology
- Reduced cost per hole compared to conventional approaches like potholing
- Reduced head count on site
- Less flights/accommodation required for remote site working
The PANDA Instrumented Dyamic Cone Penetrometer (DCP) involves driving a variable energy cone penetration device into the rail track substructure to collect the strength (and modulus by correlation) profile with depth. Condition monitoring of the rail track substructure layers is accomplished through insertion of a camera into the same hole, also called Geoendoscopy. The combined system is referred to as the PANDOSCOPE. The PANDA, PANDOSCOPE and Geoendoscopy are all systems developed by Sol Solution.
Once the PANDOSCOPE data has been processed, the results can be presented.
The right hand chart shows the Penetrogram of the PANDA cone resistance according to depth. The left hand window shows the stratigraphy of the track layers (thickness, nature and hydrous state). The degree of ballast fouling is clearly visible, even if there if there is no distinct interface between clean and fouled ballast.
Why is Rail Track Ballast Condition Important?
Rail tracks are positioned on railway ballast, a granular material, generally comprises large, angular particles of typical size ranging between 25 and 50 mm. The main functions of railway ballast are:
- to provide high load bearing capacity which reduces pressure from the sleeper bearing area to acceptable levels at the surface of the subgrade soil
- to provide rapid drainage
Rail ballast usually contains uniformly graded material creating a sufficiently large pore structure to facilitate rapid (free) drainage. When ballast is aged and degraded, fine particles accumulate within the voids (fouling) thus impeding drainage. The process of ballast fouling, when it becomes extreme, can also generate excess pore water pressure under fast moving trains (i.e., high cyclic loading), thereby reducing the track resiliency and stability (undrained).
The maintenance costs of ballasted tracks can be significantly reduced if an accurate estimation of the different types and degree of fouling materials can be related to track drainage.