PANDOSCOPE Principles of Operation
The PANDOSCOPE is a coupling of the PANDA Instrumented Dynamic Cone Penetrometer (DCP) (tip resistance vs depth profile) and Geoendoscopy (imagery from down boreholes).
PANDA Instrumented Dynamic Cone Penetrometer (DCP)
The PANDA test is an instrumented variable energy dynamic penetration test. The tests consists of driving a set of steel rods equipped with a conical tip of 2cm2 cross-section through the material by hammering an Anvil with a standardised hammer. At each hammer blow, the energy is measured in the anvil with strain gauges.
Sensors measure simultaneously the settlement or vertical displacement of the cone. All the data is transmitted to the Central Acquisition Unit. The results are displayed immediately on the Dialogue Terminal as penetrograms, graphs that show the evolution of cone resistance according to depth.
For each blow, the depth of penetration and the driving variable energy are measured to calculate the dynamic cone resistance (qd) with the corresponding depth using the Dutch Formula, shown in this figure.
- A is the cross-sectional area of the cone
- E is the kinetic energy fed into the system during the impact
- e is the penetration per blow
- P is the weight of the driven parts during impact (impact head/anvil, rods and tip)
- M is the weight of the striking hammer
The PANDA collects mechanical information including cone resistance (direct measurement) or CBR or other parameters with correlations. This is presented in graphical format, knows as a penetrogram.
The PANDA is a versatile equipment with a total weight less than 20 Kg. Within the framework of the railway use, adaptations have been made to make it even lighter and tougher.
The Geoendoscopy test uses a tiny video camera (wired to a data logger with a soft cable) to observe the soil. The camera is introduced into the hole of a previously performed PANDA DCP test (15 mm of diameter). The collection of imagery from down the borehole allows a qualitative characterization of soil.
In the railway application, it enables condition monitoring of the railway track substructure layers. The layer characterisation for ballast and subgrade includes layer identification, layer thickness, water content (qualitative), condition (ballast fouling) and even the estimation of the soil grain size distribution.
The PANDOSCOPE is the coupled use of the PANDA Instrumented Dynamic Penetration (DCP) test and Geoendoscopy, combined with sophisticated data presentation and analysis software.