Pomme de Terre Dam of Earth and Rockfill

The design and construction of a composite earth and rockfill dam in Missouri on a foundation of saturated clay overlying dolomitic bedrock are described. Control works embody a tunnel and deep channel cuts in abutment rock. Special features include dry placement of rockfill in 5-ft lifts and a drainage blanket to facilitate consolidation of foundation clay. Pore pressures during and after embankment construction were relatively high, both in the basal clay fill and in the foundation clay and are dissipating slowly in the embankment. Weathering of upper bedrock was quite variable and resulted in a pinnacled rock surface in much of one abutment. Yet, grouting of the cutoff trench and tunnel showed bedrock was impervious. Line drilling provided sound bedrock walls in the unlined stilling basin. Of interest are the contractor's choice to line drill vertical rock faces at concrete structures to minimize quantities, to divert the river flow over riprapped impervious fill for a year, and to distribute riprap to grade with hand labor.