Remedial Drilling and Grouting at Abiquiu Dam, NM and Fluid Losses in the Embankment, a Case History-Paper

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Abiquiu Dam, a rolled earth-fill dam on New Mexico’s Rio Chama, has experienced excessive seepage through fractured sandstone abutments since impoundment began in 1963. Its original foundation grout curtain was supplemented in 1966 and again from 1978 to 1980, including regrouting beneath the embankment. These later works required drilling through the dam’s impermeable core.<br /><br />Records document drilling-fluid losses in the core during both programs and during subsequent verification drilling. Some holes lost circulation for hours despite attempts to restore it with thicker drilling mud or other materials. Grout-pipe installation also involved pressure grouting, generally at about 20 psi but occasionally at substantially higher pressures. Modeling indicates that grout-column pressures could exceed local effective stresses, particularly near steep foundation benches and other low-confinement zones.<br /><br />The authors conclude that drilling-fluid pressures, surging or unstable boreholes, and grout pressures likely caused hydraulic fracturing of the core. Fractures may have extended only to the downstream chimney drain rather than through the entire core. The losses may also be associated with possible seasonal construction interfaces in the embankment or low-stress zones above abrupt changes in foundation geometry.<br /><br />The grouting programs improved curtain coverage, especially where later work used closer hole spacing, but closure was not achieved everywhere. Gaps and high grout takes remained in some areas, and grout pressures may have increased foundation permeability.<br /><br />The case highlights the risks of drilling through an earth-dam core. Current USACE guidance prohibits drilling fluids in the core and requires an approved drilling plan; staged grouting is required when casing is installed to reduce the risk of hydraulic fracture.

Keywords

Abiquiu Dam

earth-fill dam

Rio Chama

seepage

foundation grouting

drilling-fluid losses

hydraulic fracturing

impermeable core

pressure grouting

USACE guidance