隧洞外水压力是深埋隧洞施工设计的重要参数,在深埋隧洞的前期勘察阶段,难以通过传统的垂直钻孔勘探来获取此参数,工程上一般采用折减系数法对隧洞外水压力进行估算。为更精确地评价隧洞外水压力,提出了基于定向钻孔的深埋隧洞外水压力测试技术,研发了一套以存储式压力传感器为核心的外水压力原位测试系统,并应用于引大济岷工程二郎山隧洞花岗岩体洞段。利用定向钻孔对隧洞外水压力进行了全孔段测试,揭示沿深埋隧洞轴线方向外水压力分布情况,并与折减系数法的计算值进行比较分析。结果表明:①基于Pearson相关性分析,测试得到的外水压力与裂隙密集带宽度总和呈极强相关,相关性强度r=0.85;与岩体透水率呈强相关,相关性强度r=0.64;与试段埋深呈弱相关,相关性强度r=0.16。②实测外水压力比折减系数法计算结果高20.47%~42.17%。本研究通过实测手段获取隧洞在天然地下渗流场中的外水压力值比折减系数法更具真实性和可靠性。研究成果为隧洞前期勘察阶段外水压力测试提供了一种实测量化方法,为深埋隧洞的设计施工及运行安全提供了更为科学的参考。

[Objective] External water pressure is a critical parameter in the construction design of deep-buried tunnels. During the early investigation stage, it is difficult to obtain this parameter through traditional vertical borehole exploration. In engineering practice, the reduction coefficient method is generally used to estimate the external water pressure of tunnels. To achieve more accurate evaluation, a testing technology for external water pressure in deep-buried tunnels was proposed based on directional drilling. An in-situ testing system for external water pressure, with storage-type pressure sensors as its core, was developed and applied to the granite section of the Erlangshan Tunnel in Dadu River to Minjiang River Water Diversion Project. [Methods] Full-depth testing of the external water pressure in the tunnel was conducted using directional drilling to reveal the distribution of external water pressure along the axis of the deep-buried tunnel. The calculated values obtained from the reduction coefficient method were analyzed and compared. [Results] Based on Pearson correlation analysis, the measured external water pressure exhibited an extremely strong correlation with the total width of the fracture-intensive zone (r=0.85), a strong correlation with rock mass permeability (r=0.64), and a weak correlation with the burial depth of the test section (r=0.16). The measured external water pressure was 20.47% to 42.17% higher than that calculated by the reduction coefficient method. [Conclusions] Compared with the traditional reduction coefficient method, this study analyzes the external water pressure of the tunnel using water pressure values obtained from segmented and continuous measurements in a natural three-dimensional groundwater seepage field through in-situ testing methods, providing more reliable analysis of tunnel external water pressure in engineering practice. This study provides an in-situ quantitative testing method for external water pressure testing during the early investigation stage of tunnels, thereby offering a more scientific reference for the design, construction, and operational safety of deep-buried tunnels.