 Strainstall have recently installed a rock fall monitoring system on a section of cliff face in Dawlish (near Exeter). A railway line runs along side the cliff base which is part of the main Plymouth to Exeter line. The 40 metre high red sandstone cliffs are subject to erosion, making falling rocks a risk to passing trains. For some time, Network Rail have managed the risks associated with the rock fall by carrying out monthly inspections of the cliff face, with additional inspections following adverse weather condition such as heavy rain fall or severe frost, during which temporary speed restrictions are imposed.
Network Rail turned to Carrillion to develop a technical solution to the problem, and it was decided that rock netting, reinforced by vertical wire ropes, should be installed over the cliff face to hold the rocks in place. Strainstall Operations were then contracted to instrument all 57 of the ropes. 25 tonne load shackles and an accelerometer were attached to each one, which in turn were connected to a data logger system. The accelerometer is used to detect any vibration in the netting, which alerts the system of a potential rock fall. The shackles then confirm whether or not the netting is supporting a new rock fall and how large it is.
The five data loggers are linked to a site computer, which ultimately links to the Exeter signal box via broadband, enabling the signalman to see when a rock fall has occurred so he can determine what action is required in accordance with the severity of the risk identified. This means that train speed restrictions are only imposed when there is a recognised measurable risk to trains, as opposed to the current blanket restrictions. |
