29 January 2015
A very interesting slope problem appears to have developed at the site of the new Pakyong Airport in India. The airport project is described well in Wikipedia:
Pakyong Airport is an airport under construction near Gangtok, the state capital of Sikkim, India. The airport, spread over 400 ha (990 acres), is located at Pakyong village about 13 km (8.1 mi) south of Gangtok. It is the first Greenfield airport to be constructed in the Northeastern Region of India and the first airport in the state of Sikkim…The land for the airport was carved from the mountainside using massive geotechnical ‘cut and fill’ engineering works. These state-of-the-art geogrid soil reinforcement and slope stabilisation techniques were employed as traditional retaining structures and embankments were ruled out as being unfeasible. Irish geotechnical company Maccaferri executed the project that envisaged a 550 m (1,800 ft) wide, 1.7 km (1.1 mi) long corridor on which the runway and airport buildings are to be constructed. The company, which completed the project with partners Mott MacDonald and Punj Lloyd, won the ‘International Project of the Year’ award at the Ground Engineering Awards 2012 for its work in constructing 70 m (230 ft) high reinforced soil walls and slopes at the site. The project is among the tallest reinforced soil structures in the world.
The site is impressive – this is a recent Google Earth Image of the location:
Perhaps the most important aspect in terms of this blog is the very extensive slope cutting that has been required to create the bench for the airport site. Unfortunately, since the airport construction project started there have been repeated indications of slope instability on the upslope side of the airport site, although this is often reported in the media as subsidence. An example occurred this week (via the Tibet Earthquake Twitter feed):
The location of the monastery is shown as “temple” in the above image. Meanwhile, last week there were reports of landslides on other parts of the slope:
A key question must be what is occurring on this slope to cause these instability issues, and what are the implications for the airport site? Whilst the link between the airport slope works and the instability is of course not proven (and of course instability occurs naturally on slopes in this area), there must be real cause for concern.