The video cone was used to
confirm depth of the contact between the sand and gravel and the highly
weathered Chalk, which is sometimes hard to distinguish from normal
CPT's. The results from using the video cone can be of economical importance
saving a true indication of the amount of grout needed, and importantly
reducing the danger of under grouting so eliminating chances of a costly
failure. Figures 4, 5 and 6 show the different soils.
fig 4: Sand
fig 5: Clay
On
Thursday 18th April Lankelma CPT Ltd demonstrated the future in cone penetration
testing, the video cone. The cone, developed by GeoDelft, uses a small
video camera mounted in the side of the cone with a halogen light behind
sapphire glass to record a constant image as it is pushed into the ground,
see figure 1.
The resulting imagery gives you a clear undisturbed
picture of the ground with 7 times magnification allowing you to see individual
grains and colours of the material.
The demonstration was carried out on a site
where there are large solution features in chalk in filled by sand and
gravel. The solution features are to be grouted to improve their stability,
see figure 2.
Conventional CPT's were used
to profile these large features (some up to 30m in length), see figure
3
fig 3
fig 6: Chalk
The video cone can be used for any number of applications.
For example it was used on a creosote-contaminated site in Holland. The initial
SI using boreholes showed a plume in sands with a vertical extent of 3.5m. When
the video was used on the site it delimited the plume to be 1.2m thick. The
additional 2.3m found by the boreholes were cross-contamination as the borehole
was drilled. The use of the video cone saved tens of thousands in remediation
costs.
The video cone in conjunction with normal a CPT
cone giving both geotechnical and visual data could be the future of site investigation.
A future when we can truly see what we are working with.
If you would like a demo CD of the video cone or
any other information please contact Darren Ward at darrenward@lankelma.co.uk.
Alternatively you can download a video clip by clicking
here
To
view videos on this page, you will need RealPlayer. If you do not have it and
wish to download it, please click here (file size
is 5 Mb and will take approx. 10 mins to download - you only have to do this
once).
M2 Motorway
Lankelma was asked by W.S.Atkins for
Carillion Highways Maintenance to carry out an extensive test program on the
M2 motorway in Kent. In 19, 6 hour night sessions, a total of 349 tests were
carried out. Factual reporting was carried out on a daily basis. Using cone
testing techniques ensured a cost and time effective investigation.
A combination of different special cones were used in the investigation. Cone
and friction CPT’s were carried out to determine the material and grade
of the chalk layers present. Our new Gamma Cone was used to detect variations
in the natural radioactivity of the stratification. This helps to determine
between the infilled clay and the highly weathered chalk. Finally we used the
videocone for visual confirmation of the material.
Factual reporting was carried out on a daily basis allowing the investigation
to be tailored to the site conditions. Using cone techniques ensured a cost
and time effective investigation.
