Hydraulic fracture in earth and rock-fill dams

Abstract

Unsatisfactory performance of earth and rock-fill dams involving excessive seepage, piping or failure has been attributed to hydrofracture of the core. Although the phenomenon has been reported for some time, important factors influencing hydraulic fracturing pressure, such as saturation and consolidation, have received relatively little attention; nor have results of laboratory tests or theoretical study been directly related to field performance. In this paper, laboratory hydrofracturing tests under well-defined conditions were performed. A simple theoretical expression for fracture pressure is developed involving only conventional soil strength parameters. Case histories involving hydraulic fracturing of the earthcore are reviewed, and "field" hydraulic fracture pressure and crack closure pressure are defined. The results of the laboratory tests show that hydraulic fracture pressure is not a unique soil property; its value depends on the degree of saturation and consolidation. A comparison of the data deduced from case records with test results and theoretical predictions indicates general consistency. The field hydraulic fracturing pressures are bounded in the upper limit by results from saturated-consolidated tests and in the lower limit by results of saturated–unconsolidated hydraulic fracturing tests. It is suggested that the methodology presented may be useful in the assessment of risk of hydraulic fracturing of dams. Key words: earth and rock-fill dams, hydraulic fracture, tensile strength, seepage, Teton Dam.

Operation and Maintenance of Hydraulic Structures

“…It may be associated with differential foundation settlement, differential embankment compression, embankment arching, contact with concrete structures, or drying out of the upper portion of the core during prolonged dry periods (Hjeldnes and Lavania 1980;Lo and Kaniaru 1990). It also may be associated with dissolution of dispersive clays, a defective layer in the core, poor material placement, or low permeability in downstream dam shell.…”

Embankment Dams

“…Cracking manifests within zones of tensile due to differential settlement, filling of reservoir, and seismic action (Lo and Kaniaru 1990). Since cracking cannot be totally prevented, the design must include provisions to minimize its adverse effects.…”

Laboratory investigation of multiple grout injections into clay

“…As most of the previous laboratory tests are reported for a single injection (e.g. Jaworski et al, 1981;Mori & Tamura, 1987;Panah & Yanagisawa, 1989;Lo & Kaniaru, 1990;Mori et al, 1990;Lefebvre et al, 1991;Mhach, 1991;Andersen et al, 1994;Yanagisawa & Ali, 1994), a series of multiple injection tests as well as single injection tests were performed in the laboratory.…”