The PANDOSCOPE is a coupling of the PANDA Instrumented Dynamic Cone Penetrometer (DCP) (tip resistance vs depth profile) and Geoendoscopy (imagery from down boreholes).
For rail applications, the PANDOSCOPE is used as a non-destructive rail track ballast fouling and formation condition assessment method.
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 subgrade (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 maintenance and renewal strategy.
The PANDOSCOPE also provides engineering services with reliable geotechnical data for track design purposes. The knowledge of mechanical and physical properties of existing subgrade and sub ballast layers is very important for the future track design. Such data can be acquired through geotechnical tests. The PANDOSCOPE overcomes the limitations of the majority of classical geotechnical tests (rigs) carrying out such tests on revenue service lines because of existing railway constraints (e.g. limited possession times (typically 4-5 hours at night for passenger lines), track access, no destabilization of the track, limitation in height for sounding equipment for electrified lines etc).
Rail network operators like the French SNCF and those in the USA have increased their use of the PANDOSCOPE method because of its economy, speed, enhanced data collection and elimination of unnecessary track disturbance. Indeed, over 30,000 tests have been done with the light and cost effective PANDOSCOPE method for railway track characterization and ballast condition assessment.
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 hydric 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.