Technological innovations in construction of underground caverns in basaltic rocks at Baihetan Hydropower Station on Jinsha River

Abstract

The two underground powerhouses on the left and right banks of Baihetan Hydropower Station (BHT-HS) are symmetrically arranged inside basaltic rocks in the alpine gorge reach of the lower Jinsha River. Each of them is equipped with 8 sets of 1,000 MW hydraulic turbine generators, with the largest unit capacity, total installed capacity, span of main powerhouse (i.e. 34 m), diameter of dome-shaped tail-regulating chamber (max diameter of 48 m) and scale of underground caverns around the world. Due to complex layout, interaction between caverns and high hollowing rate, the construction process of the underground cavern group is faced many challenges. For example, the cavern excavation is located in the high ground stress area dominated by horizontal tectonic stress; the underlying basalt fractures are well developed, and the rock is hard and brittle, with low crack initiation strength; columnar jointed basalts develop locally; a number of large and weak gently-sloped shear zones develop diagonally cutting the main powerhouse. Following the construction ideology of “understanding, utilization, protection, monitoring, and feedback analysis on the surrounding rock masses during the construction period”, and with the engineering construction procedure of “the excavation, analysis, prediction and inspection of each rock layer”, this paper proposes a set of innovation construction technologies including “advanced pre-control, thin vertical layer, small planar partition, short excavation progress, fine blasting, strong and quick support, short interval monitoring, quick feedback, precise dynamic optimization” to control the internal cracking of the hard and brittle basaltic rocks, discontinuous deformation of staggered zones and spatio-temporal deformation of underground caverns in high geostress. It has promoted the safe and orderly construction of BHT-HS, the technical progress of the construction of hydropower station projects in China, and may also be applicable to the design and construction of similar projects worldwide.