Construction of the longest railway in the world at elevations over 4000 m presents unique opportunities and challenges to our country. The railway traverses the famous Qinghai-Tibet Plateau and covers a distance of 1118 km, from Golmud in Qinghai Province to Lhasa, the capital city of the Tibet Autonomous Region.

The Qinghai-Tibet railway travels over a 632- km permafrost zone, 550 km of which is in continuous permafrost. The Plateau permafrost has a relatively high temperature, compared with permafrost temperatures in Siberia and the Arctic, and it is therefore more susceptible to thermal disturbance. Because the plateau is both an ‘initiator’ and a ‘magnifi er’ of global change, it will most likely respond early to climatic changes, and the temperature increase on the Qinghai-Tibet Plateau will be larger than the global average. Thus, permafrost in this particular condition willbring great diffi culties to design, construction and maintenance of the railway. Counter-measures to protect the permafrost and cool the subsoil must be taken because of the relatively hightemperature permafrost and the global warming. To monitor the situation, several different engineering tests are conducted based on principles of controlling radiation, conduction and convection. The tests for example concern shading the sun, using insulation material, changing the height of embankments, using heat semi-conductors, increasing ventilation, using thermopiles, using crushed stone embankment etc. So far, the idea of protecting the permafrost and cooling the subsoil has been applied widely to design and construction of the Qinghai-Tibet railway. Meanwhile, research on the following topics are conducted: How does the climate change ? How is permafrost responsible for climate change ? How is permafrost changed during engineering action ? How is permafrost changed with both climate change and engineering action ?

The Sixth Chinese Conference on Glaciology and Geocryology and International Symposium on Permafrost Engineering was held in Lanzhou, 19-22 September 2002. It was sponsored by the Chinese Society of Glaciology and Geocryology, the State Key Laboratory of Frozen Soil Engineering and Ice Core and Cold Regions Environment Laboratory of the Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academic Sciences, and co-organized by the Civil Engineering School of Lanzhou Railway University. About 130 representatives from thirty-three universities and research institutes in China, USA, Canada and Germany attended the conference. The symposium had three main topics: Cryosphere and the change of global climate; Engineering in cold regions and the Qinghai-Tibet railway; Basic physical and mechanical properties of ice, snow and permafrost. Post-conference fi eld excursions took place 23-30 September. The fi rst trip went from Lanzhou to Golmud with a stop at Dunhuang city. The second trip went from Golmud to Lhasa city along Qinghai-Tibet roadway, and studied permafrost-related and geotechnical problems in the construction of the Qinghai-Tibet railway.

Ma Wei (