Building on firm foundations.
If the engineers responsible for the construction of the tower
in Pisa had access to the specialist soil testing equipment
designed and produced by GDS Instruments Ltd, then it
may never have gained such fame as the 'leaning' tower.
Based in Hook, Hampshire, GDS has more than a quarter of a
century's experience of developing top quality soil testing equipment
that today enjoys a well-earned reputation with research and testing
laboratories around the world. Playing a key role at the heart of this
equipment are LVDTs supplied by RDP Electronics Ltd.
Screen display from the test setup
Determining how soil samples perform under load provides critical
data for engineers concerned with calculating building loads for
foundations of structures such as dams, bridges, railways and buildings.
GDS has developed a triaxial testing system where cylindrical soil
samples are subjected to a confining pressure, an internal pressure
and then use LVDTs to measure axial and radial strain in order for
engineers to understand how the ground itself will deform.
Test sample showing radial and axially
mounted LVDT sensors
For test purposes the soil sample is encased in a rubber membrane
and sealed with a top cap. Low pressure (up to 3500kPa) versions
of the system use water as the confining medium and high pressure
(up to 200 MPa) use oil. A confining pressure is applied to simulate
the surrounding soil and an internal pressure is applied within the
A pair of RDP's D5/200H LVDTs are mounted in radial callipers
to create a local strain measurement device while a further LVDT
measures axial strain. According to Associate Director Clayton
Dodd, RDP's D5 LVDT5 are selected because, 'they are small
and light and so minimise disturbance to the sample'. As the
sample 'barrels' under axial load, the LVDTs pick up these very
small movements, accurately outputting data to a GDS signal
conditioning and data acquisition unit.
Within the Data Acquisition unit are three RDP S7AC in-line signal
conditioning amplifiers that convert and amplify the output from the
LVDTs in the test set-up. This output is utlised by GDS's specially
developed software to produce graphical and numeric data that
is presented on a PC screen.
For sales and technical information contact:-
RDP Electronics Limited
Grove Street, Heath Town, Wolverhampton WV10 0PY. UK.
Tel: +44(0) 1902 457512. Fax: +44(0) 1902 452000