01.01.07
The new rail CPT truck
The new rail CPT truck, unique to Lankelma, has dramatically improved productivity in rail soil investigation. Soil tests can now be completed in 40 minutes and results are displayed real time, making it the ideal vehicle not only for weekend possessions but also for short weekday possessions
The condition of the soil under the track can now be assessed to a level of detail previously unavailable, providing supporting data for propositions such as increasing speed limits or rebuilding earthworks.
A cone penetration test (CPT) is performed by pushing an instrumented cone into the ground at a constant rate, with measurements recorded every 20mm. An instant analysis is displayed on a screen in the rail truck. In normal use the cone produces no spoil, although it does have the facility to extract a sample if required.
The rail CPT truck recently completed a large embankment research investigation for two reasons. Firstly, to look at the material of the embankment along its whole stretch. This was done by carrying out standard CPTs through the 4-foot. The tests were carried out at 50m intervals, over a length of 700m and down to a maximum depth of 15m.
Secondly, to carry out some work for a Network Rail research project. These works were carried out in a small test area at one end of the embankment. Two piezocones were carried out using a face filter. Testing through ballast using a piezocone normally results in the cone de-airing. To stop this from happening, starter pits were dug through the ballast and a plastic tube was inserted and back filled around. The face filters give better excess pore pressure results compared to the shoulder position, but are much weaker. Samples of the material at the interface between the ballast and subgrade were taken for analysis.
Three seismic CPTs (SCPTs) were also carried out down to a depth of 15m. These were done to look at the shear wave velocity through embankment with depth.
All testing was carried out over three shifts in a 27 hour possession.
Track access was gained at a level crossing, the rail wheels lowered, and the truck driven to where the ground investigation was needed. Ballast sampling and GPR can be carried out at the same time as the CPT.
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