Impacts of landslides on trunk roads in Scotland

Once again I present you a very dated case study – I must have preempted this as I have since moved to Scotland so this suddenly seems interesting again.

Scotland is connected by a series of trunk roads. Trunk roads are roads of strategic importance and closure of one of these roads can have widespread impacts. Scotland’s trunk roads carry 35% of all Scottish traffic and are valued at £20.8 billion. In August 2004 there was a series of landslide events across Scotland. The landslides affected key parts of the road network and limited access to travel and services, highlighting the potential financial implications of landslides (Table 1).

Table 1: Major landslide events that impacted on the road network
Date August 2004 October 2007 
Road(s) A83 A9 A85 A83
Vehicles per day 5,000 > 13,500 5,600 5,000
Consequences Closed 2 day Closed 3 days 57 people airlifted to safety,

Closed 4 days

Closed for 17 days, Diversion of 70 minutes
Cost £395,043 £921,766 £685,405 £1,693,401
Rest and Be Thankful, A83

As a result, the Scottish Road Network Landslides Study (SRNLS) was published in 2005 with the aim of reducing the disruption to tourism and local and commercial road users as a result of landslides. The SRNLS used a GIS-based assessment to identify the most at-risk areas which were then assessed in closer detail. One these sites is the Rest and Be Thankful area on the A83 which and is highlighted in the figure below. 

Rest and Be Thankful Area of Influence

The impacts of a landslide on a road system go beyond the loss of use of the road; there is a lack of access to services for goods, employment, education and health. As a result road closures on trunk roads create a vulnerability shadow, the closing of a 100m section of road on the A83 in 2007 caused a vulnerability shadow of 2800km2 (seen above).

A variety of hazard reduction measures have been put in place as a result. A rain gauge has been installed as landslides are most likely to happen in times of heavy rain. These have been successful as they contribute to the understanding of landslides and local weather patterns as well as for prediction purposes. Furthermore, regular controlled explosions of large boulders have been undertaken, and protective fencing and netting have been installed.

Netting at the site

However, these are temporary fixes and require maintenance. Long-term solutions include the planting of vegetation to increase slope stability. This takes into account environmental impacts and needs little upkeep. Furthermore, the option of planting vegetation will also contribute to the improvement of noise and fume pollution.

Furthermore, the use of technology has been effective at the site. Tilt sensors which provide information in real time installed post the 2005 review has closed the road successfully in anticipation of landslides on several occasions. However, closure of the road creates lengthy diversions (Table 1). Hard engineering options have been considered such as the building of a tunnel or redirecting the road, though these were deemed as too expensive for the perceived risk.

In conclusion, closure of a trunk road is not an option, and the landslide hazard assessment is an effective way of mitigation cost, the risk to life and disruption to infrastructure.While successful at warning of imminent landslides, more action could be taken on preventing them in the first place such as improving drainage under the road and the planting of vegetation.

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