The Neelum–Jhelum Hydropower Project, commissioned in April 2018 and located in the Azad Kashmir region of northeast Pakistan, is one of the most challenging and technically complex projects in the region. The project’s 28.6 km headrace tunnels are constructed in a highly mountainous region with relatively complex geology that includes various sedimentary rocks of Murree formation. The hydro-mechanical behavior of the deep headrace tunnels with a maximum overburden of 2000 m and underground powerhouse at a depth of 450 m are of particular interest. The project generates electricity by diverting water from the Neelum River to an underground powerhouse through a tunnel system crossing beneath the Jhelum River. The pressurization of the hydraulic tunnels was an important milestone and necessitated intentional planning down to the smallest detail for the first filling. Successful filling was a governing criterion for proper functioning of the tunnel lining that was supplemented by monitoring instruments, a drainage system, and ground treatments during construction of the project. Ground re-saturation during the first filling of the concrete and shotcrete-lined waterways constructed in the diversified rock mass is interesting to study. The rock mass in this area is sheared and fractured, with open fissures. In this study, we investigated the ground re-saturation and water leakages in adits, plugs, and surface outflow after the first filling of the headrace tunnel. A load rejection test was conducted to evaluate overall fitness of the power waterways, plant, and to study any change in leakages due to sudden oscillation in the waterway tunnels. Surfer3D software was used to analyze the data collected from the piezometers, which showed abnormal water pressure built up in a localized zone between penstocks three and four. This study was also supported with two-dimensional finite element modeling of the project, at a location where the tunnel has minimum rock cover susceptible to hydrojacking. Numerical analysis results were compared with field data results during the first filling process and both showed close proximity.

中文翻译：

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衬砌压力隧道首次充填期间的地面饱和度响应：案例研究

Neelum-Jhelum 水电项目于 2018 年 4 月投产，位于巴基斯坦东北部的阿扎德克什米尔地区，是该地区最具挑战性和技术复杂性的项目之一。该项目的 28.6 公里引水隧道建在一个多山地区，地质相对复杂，包括 Murree 地层的各种沉积岩。最大覆盖层为 2000 m 的深引水隧道和 450 m 深度的地下厂房的水力力学行为特别令人感兴趣。该项目通过穿越杰赫勒姆河下方的隧道系统将尼勒姆河的水分流到地下发电厂来发电。液压隧道的增压是一个重要的里程碑，需要有意识地规划到第一次填充的最小细节。成功的填筑是隧道衬砌正常运行的管理标准，在项目施工期间辅以监测仪器、排水系统和地面处理。研究在多样化岩体中建造的混凝土和喷射混凝土衬里水道的第一次填充期间的地面再饱和是很有趣的。该地区的岩体被剪切和破碎，具有开放的裂缝。在这项研究中，我们调查了引水隧道第一次充填后地沟、塞子和地表出流中的地面再饱和度和漏水情况。进行了负载拒绝测试以评估电力水道的整体适应性，工厂，并研究由于水道隧道突然振荡而导致的泄漏变化。Surfer3D 软件用于分析从压力计收集的数据，这些数据显示在压力管 3 和 4 之间的局部区域建立了异常的水压。该研究还得到了项目二维有限元建模的支持，在隧道具有最小岩石覆盖层的位置容易发生水力提升。数值分析结果与第一次填充过程中的现场数据结果进行了比较，两者都非常接近。该研究还得到了项目二维有限元建模的支持，在隧道具有最小岩石覆盖层的位置容易发生水力提升。数值分析结果与第一次填充过程中的现场数据结果进行了比较，两者都非常接近。该研究还得到了项目二维有限元建模的支持，在隧道具有最小岩石覆盖层的位置容易发生水力提升。数值分析结果与第一次填充过程中的现场数据结果进行了比较，两者都非常接近。