研究目的:以兰渝铁路桃树坪、胡麻岭隧道施工为切入点，结合施工遇阻情况，重点分析兰州地区第三系砂岩地质背景、成岩特征、物理力学性质以及对隧道施工工作的不利影响。在大量施工数据，观测记录基础上，开展水稳性特征的专项科研攻关，增强对兰州地区第三系砂岩认识程度，提出较为前沿的施工处理方法。
研究结论:第三系砂岩具有异常复杂的水稳性特征，围岩受扰动及水浸泡影响，稳定性随时间显著变差，在国内外地下洞室施工中极其罕见。超前降水控制围岩含水率低于砂岩塑性变形含水率，保持围岩处于基本稳定状态，是有效解决第三系含水砂岩稳定性的重要措施。
Research purposes: Taking construction of the Taoshuping Tunnel and Humaling Tunnel of Lanzhou －Chongqing Railway as the breakthrough point and Combined with the construction difficulty，this paper analyzes the geological background，diagenetic characteristics，physical and mechanical properties of the tertiary system sandstone in Lanzhou area and their adverse effects on tunnel construction． Base on a large number of construction data and the observational records，the special research was done on the water － stability characteristics in this area to better understanding of them．The advanced treatment methods was put forward for construction．
Research conclusions: The tertiary system sandstone has unusually complex water － stability characteristics． Affected by the disturbance of surrounding rock and groundwater，its stability becomes worse obviously with time going on． Such situation was rarely seen in construction of underground cavern at home and abroad． The advanced lowering the groundwater for controlling the rate of water content of the surrounding rock below the the rate of water content of the plastic deformation of the sandstone rock and keeping the surrounding rock in basic stable state are the effective ways to solve the stability of the tertiary system sandstone．
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