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由于尼泊尔喜马拉雅地区岩石强度较低,水平应力较高,因此在该软弱构造片岩带中开挖隧洞具有较大的挑战性。文章主要阐述装机容量为650 kW的塔玛科什3级水电工程17km长大跨度隧洞和大型地下发电厂房(这两项工程计划穿越夹杂有软弱构造片岩带的坚硬眼球状片麻岩区域)所面临的重大技术挑战。穿过片岩带开挖的隧洞长度约占总长的15%,由于此岩层带岩石强度较低,具有剪切特性和渗流现象,且水平应力较高,围岩挤压和隧洞塌方都是可预期的问题,因此该工程地下开挖主要关注的问题是大尺寸隧洞的可施工性和工期。为了解决可预期问题,进行了更进一步的研究,主要集中在隧洞最大可建尺寸、方位、减少围岩挤压的开挖方法,以及地下发电厂房稳定性和合理岩石支护设计上。研究发现,在构造片岩带中可施工的全断面隧洞最大尺寸可达9m,为改进的马蹄形(有弧形仰拱)。通过对隧洞三种不同方位方案(即正交、斜交、平行)的分析发现,与叶理面正交的方案最佳,可减少围岩挤压近50%。
Due to the low rock strength and high horizontal stress in the Himalaya region of Nepal, it is more challenging to excavate tunnels in this weak structural schist belt. The paper mainly describes the 17km long-span tunnel and the large underground powerhouse of the Tamarkax Class III hydropower project with an installed capacity of 650 kW, both of which project through the hard and gneissic gneiss area with weak structural schist belt Faced with major technical challenges. The length of the tunnel dug through the schist belt is about 15% of the total length. Due to the low rock strength, shear characteristics and seepage phenomena and high horizontal stress in this rock zone, the surrounding rock extrusion and tunnel collapse are both predictable Therefore, the main concern of the underground excavation project is the construction of large-size tunnel and the construction period. In order to solve the predictable problems, further studies were carried out, focusing on the maximum size and azimuth of the tunnel, the excavation method of reducing the surrounding rock extrusion, the stability of the underground power plant and the design of reasonable rock support. The study found that in the construction of schist belt can be constructed full-size tunnels up to 9m in size, is an improved horseshoe (arched arch). Through the analysis of three different azimuth schemes of the tunnel (ie, orthogonal, skewed and parallel), it is found that the scheme orthogonal to the leaf surface is the best, which can reduce the compression of surrounding rock by nearly 50%.