Did the earth move for you? Load cells and landslides
Land slides may not be that common in the UK, but they can be incredibly disruptive when they do happen. The recent heavy rain, for example, caused a land slip on the main rail route into from London to Southampton, and required some major earth removals before the services could continue. Luckily, load cells can play their part in monitoring structures holding back the flow of earth.
Holding back the mountain
The issue of landslides takes on a while new dimension in the 10 Mile Slide region of British Columbian, Canada. The clue is in the name, as the region marks the edge of a post-glacial earth flow known as Tunnel Earth. In practice this means 13 million cubic metres of soil and rubble poised on a slope of the the coastal mountain range. This is in close proximity to a CN Rail railway line and Highway 99, the main route to the popular ski resort of Whistler and on to Lillooet and Kamloops.
The 10 Mile Slide section may only be 200 metres wide and 300 metres long, but with a depth of 18 metres, that’s still approximately 1 million cubic metres of earth creeping forward for years. As an article in the Journal of Commerce explains, the Ministry of Transportation and Infrastructure (MOTI) invested $60million for “tying down the mountain of dirt” with a programme of major soil anchor work.
Anchors and rods
Phase 1 invovled installing 44 precast anchor blocks with double corrosion protected (DCP) anchor bars made from 65mm Grade 150 Hot Rolled Threaded Bars.
“The anchors were drilled into the bond zone, which was undifferentiated glacial sediment, holding back the slide and transferring the load from the anchor into the ground. The bond length is composed of corrugated high-density polyethylene (HDPE) pipe encapsulating the pre-grout anchor bar, where the corrugation provides bonding between the anchor bar and the soil.”
Due to the remoteness of the site, off-site monitoring had to be by satellite (there is no mobile phone reception at the site). So the team decided to use vibrating wire load cells, a data logger and satellite-specific software for real time monitoring. The load cells offered significant advantages over the project-specified strain gauges which would have needed to been installed before each anchor was installed. Instead:
“The load cells on the bearing plates can be easily reused or replaced and indicate when the anchors are over-stressed and need to be de-tensioned or locked off.”
Load cells and landslides
Whilst this example is quite dramatic, load cells are used across the world every day to give early warning of earth movements around vital rail infrastructure, including:
- retaining walls at Italian rail stations
- areas with unstable rock mass in close proximity to rail tracks (they have great diagrams!)
- load cells installed on rail bridges and viaducts
- as part of the Development of Landslide Risk Assessment Technology along Transport Arteries in Viet Nam using shear load cells and stress load cell
Need specialist load cells for a major project?
Call us. We can help design a system to provide the level of monitoring you require, and relay the data in real time via cabled, wireless or other remote monitoring systems. We can also design and manufacture bespoke load cells to your specifications, or supply from our extensive stock here at our manufacturing base in Reading, UK.
