Excavation Shaping and Damage Control Technique for the Breccia Lava Dam Foundation at the Bai-he-tan Hydropower Station: A Case Study

Due to complex geological conditions and strict requirements of excavation shaping and damage control for the breccia lava dam foundation, the development of a suitable dam foundation excavation technique become one of the most challenging technical issues during the construction of the Bai-he-tan hydropower station. To resolve this challenge, this paper develops a new energy-relief blasting (ERB) technique that uses a shock-relief structure arranged at the bottom of a borehole. The energy-relief structure consists of a spherical energy-relief block with high sonic impedance and a flexible cushion with low sonic impedance. The resulting reflection of the stress wave at the spherical shock-reflection block surface and the buffer effect of the flexible cushion can help to reduce the damage caused by the explosion load on the foundation rock mass. Furthermore, considering the irregular surface of breccia lava, the vertical boreholes used in ERB can solve the problem of drilling horizontal boreholes when using traditional excavation techniques, markedly improve construction speed. To verify the quality of the excavation shaping of the new technique, three comparative experiments were carried out at the Bai-he-tan hydropower station during field production. The results indicate that the ERB excavation technique can effectively control blast-induced damage in the host rock, protect the foundation rock mass, and yield a smooth foundation surface. Owing to the good excavation quality and high construction efficiency of the new technique, ERB has been successfully applied to the excavation of the left bank of the breccia lava dam foundation on a large scale. This new technique has wide application prospects in dam foundation excavation and other engineering fields.