A38 Western Interchange, Liskeard
Geotechnics Limited were commissioned to undertake a ground investigation to assess the ground conditions behind the four wing walls supporting the A38 at the Western Interchange near Liskeard, Cornwall and monitor any movements of the walls.
In order to do achieve this, several methods of ground investigation were required, along with in-situ and laboratory testing and instrumentation. However, the access to site was quite restricted and needed to be carried out within traffic management with specific time constraints. The slopes of the wing walls were relatively steep and sections of crash barrier also had to be removed to gain access.
The investigation comprised trial pitting, hand held window sampling and hand excavated inspection pits on the slopes of each wing wall, windowless sampling and dynamic probing at the crest of the wing walls. Subsequent laboratory testing to obtain specific details on the properties of backfill, such as effective angle of internal friction was also undertaken.
In order to measure and monitor the rotation of the walls in the vertical axis, six uniaxial Tiltmeters were installed on three of the walls at approximately 1/3rd and 2/3rd height. The cables were routed and hard wired into a datalogger mounted on one of the wing walls. These were installed using a scissor lift enabling access to heights of over 6 metres up the faces of the walls.
An existing datalogger with solar panel, installed in 2000 for use with strain gauges, was inspected and deemed to be unsuitable for monitoring of the tiltmeters. This datalogger was removed, but the solar panel was suitable for keeping the battery in the new multi-channel datalogger fully charged.
Remote monitoring was made possible by equipping the datalogger with a GSM modem, which transmits data to an off-site server. Argus monitoring software then processes the data and presents it on a website for real-time viewing by the Client.
The wing walls will be monitored for movement for 18 months and the data collected will hopefully confirm whether the walls are actually moving!