Study on Deformation and Control Measures of Columnar Jointed Basalt for Baihetan Super-High Arch Dam Foundation

Abstract

The Baihetan super-high arch dam is constructed under complicated geological conditions, including large-scale columnar jointed basalt with closely spaced joints and multiple interlayer and intralayer shear belts at the lower part of dam base. Due to large excavation depth and scale at the dam base, unloading deformation and relaxation of columnar jointed basalt and shear belts were revealed by field investigation, in situ testing, monitoring, and numerical simulations. It was found that the relaxation depth of columnar jointed basalt was related to geostress, rock mass quality, and gently dipping shear belts. The time effect of unloading relaxation is also obvious in the columnar jointed basalt. In terms of unloading deformation control, comprehensive reinforcement measures and proper construction sequence at the dam base were proposed, including reservation of a 5-m-thick rock mass layer as the protective layer, consolidation grouting on the protective layer, preinstallation of mortar anchors through consolidation grouting hole, excavation of protective layers with controlled blasting in small benches, timely anchorage by prestressed cables upon exposure of foundation surface, and additional consolidation grouting for shallow foundation rock mass under concrete cover weight. With the comprehensive reinforcement measures at the dam base, the relaxation depth of columnar jointed basalt was small and shear deformation of shear belts was effectively controlled. Thus, the proposed reinforcement measures were proven to be proper and effective, which could meet the requirements of dam base and provide some reference for similar hydropower projects.