Foundation Practices for Talbingo Dam, Australia

The dam site for Talbingo Dam, a 530-ft high rockfill structure, is located in shyolite lava flows except for the upper right abutment, which is in tuff beds. On the right abutment the rock is generally hard, durable and broadly jointed, but on the left abutment the rock is more weathered and relatively soft at the surface. Most of the dam site was covered with 2 ft to 5 ft of soil. Surface stripping was nominal on the left abutment but special treatment was required on the right abutment because of the presence of the weathered tuff. To assume an impervious cutoff, a cutoff trench was used and in some areas the rock was excavated to depths of 50 ft. Extensive foundation preparations, utilizing air and water jets, thick grout, mortar and concrete was also used in the core contact zone; in addition, a 2-ft layer of the more plastic soil compacted wet of optimum was placed against the abutments to further reduce the possibility of seepage along the core contact. Blanket and curtain grouting were also performed as an integral part of the foundation treatment.