在高原、高寒地区修建单线单洞特长隧道，面临隧道勘察选线、施工方法选择、长距离通风、深竖井施工、生态脆弱区环境保护以及低氧环境下施工等一系列世界性技术难题。结合敦煌至格尔木铁路当金山特长隧道的设计全过程，对特长隧道的勘察设计进行全方位介绍。针对当金山特长隧道“三高（高海拔、高地应力、高地震烈度）”、“两低（气温低、气压低）”的地域特点，以及“三长（单面坡长、独头通风距离长、反坡排水距离长）”、“两多（断层破碎带多、不良地质多）”、 “两大（埋深大、水量大）”等工程特点，对“钻爆法、TBM法、钻爆法+TBM法”3种施工方案进行系统的经济技术比选，最终确定大型机械配套的钻爆法施工方案。最后对单线铁路特长隧道的设计与施工提出了一些建议: 1）特长隧道选线时重视物探技术； 2）处理好勘察与设计的关系； 3）高海拔特长隧道应加大机械化施工； 4）特长隧道应充分发挥平行导坑的作用； 5）重视环境设计。

For superlong singletube singletrack railway tunnels in extremelycold highplateau area, worldlevel technological challenges in surveying and alignment selection, construction method selection, longdistance deadend ventilation, deep vertical shaft sinking, ecologicallyfragile environment protection and tunneling in lowoxygen environment are faced. In the paper, the design of superlong Dangjinshan tunnel on DunhuangGolmud railway is presented. Dangjinshan tunnel has the following characteristics: 1) high altitude, high ground stress and high seismic intensity; 2) low temperature and low atmospheric pressure; 3) long singledirection slope, longdistance deadend ventilation and longdistance antislope water releasing; 4) lots of fractured zones and lots of adverse geological units; 5) deep cover and serious water inflow. Comparison and contrast is made among three construction methods considered for the tunnel, i.e., drill and blast method, TBM method and “drill and blast + TBM” method, in terms of economy and technology, and drill and blast method assisted by heavyduty construction equipment and machinery is proposed for the tunnel. Finally, the following advice is made on the design and construction of superlong singletrack railway tunnels: 1) More attention should be paid to the geophysical prospecting technology in the selection of the alignment of superlong tunnels; 2) The relationship between the survey and the design should be well dealt with; 3) Mechanized construction should be adopted for superlong tunnels in highplateau area; 4) The function of the parallel service gallery should be fully used; 5) More attention should be paid to the design of the environment protection measures. 