Cedar Lake, a privately owned, man made lake
in central Oklahoma mysteriously failed November 7, 1986.
The 75 acre lake, 30 feet deep at the dam, dropped 15 feet
within a 36 hour period. Water exited the ground 250 yards
downstream of the earth fill dam leaving the embankment
intact.
The dam was located in the lower section of
a highly fractured, loosely cemented sandstone formation.
The most likely cause for the failure was creation of a
communication route between the preexisting fractures and
the waterbearing sandstone reservoir below the lake bed.
Western Sportsmen Club, owner of the dam,
awarded a $456,000 contract to The Judy Company to repair
the dam. Repairs included enlarging the breached section of
the dam, performing drilling and consolidation grouting, and
construction of a grout cutoff wall.
No significant voids were encountered where
the failure was suspected. Drilling continued along the
right abutment where voids from 2 to 3 feet were located
above the unconsolidated zone. Voids as much as six feet
were subsequently encountered up to 215 feet away from where
the failure was suspected.
891 C.Y. of sand/fly ash consolidated fill
and 250 C.Y. of cement pressure grout were placed. Four
piezometers were installed at the downstream toe to continue
monitoring the groundwater level as the lake filled.
The Judy Company services were performed
under the direction of Pat Carr with Dean Van Gorp
supervising in the field. McCormick Engineering provided
plans and specifications. The project was inspected by Cecil
Bearden of the Oklahoma Water Resources Board.
