The Application of Self Drilling Anchor Bolt at the Tala Hydro Project for Tunneling in Poor Rock Mass Conditions

Time:2015-08-20View:

The Tala Hydroelectric Power Station in Bhutan has been a remarkable feat of engineering, harnessing the power of the Wangchu River to generate clean and sustainable energy. However, the construction of this project faced significant challenges due to the poor rock mass conditions in the area. Fortunately, the implementation of Self Drilling Anchor Bolts revolutionized the construction process, offering a robust solution to overcome the demanding geological conditions.

Project Background

Tala Hydroelectric Power Station is a run-of-the-river type hydroelectric power station on the Wangchu River in Chukha District, Bhutan. The run-of-the-river project is being managed by Tala Hydroelectric Project Authority (THPA). It is located on the Wangchu River and, at 860m, is the region’s largest high-head project. The station consists of a 92-metre (302 ft) tall gravity dam which diverts water through a 22 km (14 mi) long headrace tunnel to the power station. For the more details about the Tala Hydroelectric Power Station you can refer at Wikipedia-Tala Hydroelectric Power Station.

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Originally slated for completion in June 2005, the project faced significant geological hurdles, ultimately delaying its commissioning until March 2007. The rock formations, primarily Thimphu gneiss, exhibited challenging characteristics, including joint sets, fault lines, and varying thicknesses of foliation shears.

Problem and Challenge

Within the project site, the rock type is biotite gneiss with bands of quartzite, mica schist, and sericite schist with amphibolite. Rock conditions merit 3 - 4 on the NGI Q system, areas such as C2, C-3, and all of C-4 presented poor rock mass conditions, warranting urgent stabilization measures. Moreover, during excavation, the powerhouse and penstocks revealed a wide variance from the anticipated rock classification. The fragmented strata, prone to instability, posed a significant threat to the progress and safety of the construction efforts.

Solution

To overcome the geological challenges and ensure the structural integrity of the Tala Hydro Project, a pioneering solution was needed. Self Drilling Anchor Bolts emerged as the ideal choice to stabilize the desilting chamber walls and facilitate tunneling in poor rock mass conditions.

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Construction Technology

The application of Self Drilling Anchor Bolts brought about a seismic shift in the construction approach. These innovative rock bolts enabled simultaneous drilling and anchoring, drastically reducing installation time and mitigating the risk of hole collapse. At Tala, they played a pivotal role in stabilizing the RCC wall of Desilting Chamber No.3, where extensive cracks were detected during borehole camera investigations. The fragmented strata posed a challenge, making it difficult to maintain drilled holes long enough for the installation of longer rock bolts.

The construction team employed Self Drilling Anchor Bolts strategically, using a combination of 114 anchors with 20m length and 38mm diameter, spaced at 3m, and an additional row of 36 anchors with 24m length and 51mm diameter, also spaced at 3m. By securely anchoring the chamber walls to the deeper competent rock, these bolts provided the much-needed stability and ensured the safe continuation of the project.

Conclusion

The Tala Hydro Project serves as a remarkable testament to the power of innovation and adaptability in the face of challenging geological conditions. Through the application of Self Drilling Anchor Bolts, the construction team successfully overcame the obstacles posed by poor rock mass conditions, ensuring the stability of critical structures and facilitating tunneling operations. This case study highlights the importance of advanced construction technologies and showcases the pivotal role played by Self Drilling Anchor Bolts in the success of complex projects like the Tala Hydro Project.

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