California Aqueduct Foundation Repair Using Multiple Grouting Techniques

On June 5, 2001, a major leak was discovered beneath the California Aqueduct embankment at Mile Post 4.25, discharging more than 4,200 L/min (1,100 gpm) at its peak. This situation prompted emergency action to control the leak to avert breaching the embankment. The leak was plugged after pumping 42 m³ (55 yd³) of concrete to fill the large piping void. Then a geologic exploration was conducted to delineate problematic zones beneath the embankment, followed by several grouting techniques used to investigate and improve the distressed foundation. The comprehensive grouting program included 27 compaction grout holes to explore and densify the soft alluvium foundation, 13 permeation grout holes to investigate and fill voids in the underlying fractured bedrock, and abandonment of an obsolete seepage collection system beneath the Aqueduct. This paper shows chronologically how data collected from the grouting program, geologic exploration, and construction records were used to better understand the mechanisms of the piping failure.