The key technical points of design and construction of extremely large-span loess tunnel, i. e. high slope protection of tunnel portal, rapid tunneling, crossing underneath existing buildings and structures, tunnel deformation control,sinkhole backfill treatment of ground surface and ground surface fissures treatment measures, are discussed by taking engineering projects as examples. Some conclusions are drawn as follows:1)The tunnel portal excavation scheme should be selected according to the actual conditions; the high slope scheme can be adopted if it was of great risk by early tunnel portal excavation scheme. 2)Large tunneling footage should not be suggested when three-bench seven-step excavation method is adopted; the construction organization optimization, working procedure connection strengthening, short footage and rapid cycling are the keys. 3)The settlement of loess tunnel can be effectively controlled by adopting partial excavation method, strengthening advance support, decreasing excavation footage and closing inverted arch timely. 4)As for the sinkhole,the backfilling measure by using lime-soil with ratio of 3:7 and liquid cement is reliable. 5)The ground surface fissures are apt to occur in shallow-buried section and can be control by tunnel supporting;as for the existing fissures,effective measures should be taken in time.%针对特大跨度黄土隧道设计和施工过程中遇到的问题,结合工程实例,重点探讨洞口高边坡防护、快速掘进、下穿建(构)筑物措施、洞内变形控制、地表陷穴回填以及地表裂缝处理等技术要点,得到以下主要结论:对于黄土隧道的进洞方案,可根据实际情况进行灵活选择,如果"早进洞"存在风险时,也可选择高刷方进洞方案;三台阶七步法快速掘进不宜一味追求进尺,优化施工组织,加强工序衔接,实现短进尺、快循环才是关键;黄土隧道的沉降可以通过采取分部开挖、加强超前支护、减小开挖进尺和及时封闭仰拱等措施进行有效控制;黄土陷穴采用三七灰土、沙泥浆回填措施是可靠的;隧道浅埋段地表裂缝不易避免,但可通过洞内控制措施来减小其规模,对于已经出现的裂缝,应及时处理.
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