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.

Loading tests on two timber piles and a Franki pile, embedded principally in a stiff clay, were carried out. Analysis of the results appear to indicate that the adhesion of the piles is the fully mobilized undrained shear strength of the clay. Reasons for this apparent anomaly with data reported in the literature are suggested.Pore water pressures set up in the soil adjacent to the piles during load testing were very small and calculations in terms of effective stresses, indicated that the ratio of horizontal to vertical effective stress at failure is approximately 1.2.

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