In order to study the safety issues in the excavation of long and large cross-section loess tunnel with CRD method, with reference settlement of ground surface and primary support is measured, and test and analysis of the settlement in the processes of primary supporting and support demolishing and the change of internal force are conducted with reference to the practices in the high speed railway between Zhengzhou and xi’an. The results show that: CRD method can ensure the safety of excavation in large cross-section loess tunnel; sandy shallow buried loess section of the surface subsidence value is over 20 cm; the temporary end brace transverse swing is up to 9. 8 cm; when the demolition of temporary support arch sinks 2 mm and the range of demolishment is more than twice of the tunnel excavation width, the arch sinking grows significantly, reaching 40% of the settlement before demolishing. Research conclusions:temporary bearing brace stiffness should be strengthened in the design; in comparison with three-steps method, CRD method is ineffective to quick closing of inverted arch to control final settlement;the control of surface subsidence is not obvious; the length of support demolition should be controlled.%为了研究长段落大断面黄土隧道CRD法开挖安全问题,依托郑州至西安高速铁路工程实例,开展地表及初期支护沉降量测,临时支护内力及拆除临时支护过程的沉降、内力变化测试分析。研究结果表明：CRD法能保证大断面黄土隧道的开挖安全；砂质黄土浅埋段地表沉降值多在20cm以上；临时竖撑横向摆幅达9.8cm；逐榀拆除临时支护时拱部下沉2mm,拆除范围大于1倍隧道开挖宽度时,拱部下沉增长显著,达到拆除前下沉量的40%。研究结论：设计中应加强临时横竖撑刚度；相比三台阶法,CRD法不利于仰拱尽快封闭而控制最终沉降,地表沉降控制效果不明显；控制拆撑长度。
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