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The 1999 Glen Creek Landslide provides an example of a negative result of human interaction with a complex geologic environment. Excavation during mass grading exposed the basal rupture surface of an old, static landslide and weak shear zones within the weak claystone, leading to translational failure.

During remediation of the active landslide, the excavation for the buttress keyway exposed a downslope-dipping, deep-seated shear zone and reactivated it. The shear zone projected under an adjacent structure, and movement of the shear zone produced deflections in slope inclinometers located between the structure and the excavation.

The events leading to the failure of the Glen Creek Landslide represent a failure in application of the four Jahnsian steps to geologic safety: (1) hazard recognition, (2) site characterization, (3) risk assessment, and (4) hazard mitigation. First, the developer's geotechnical consultant failed to recognize the old landslides. Second, the extent of shearing within the claystone was not characterized. Third, the risk of translational failure along weak shear zones was not realistically evaluated. Lastly, mitigative measures were not implemented to address the risk of slope failure.

The postfailure mitigation of the Glen Creek Landslide was not planned with the Jahnsian steps in mind either. The potential for block failure along deep-seated shear zones was not recognized. Subsurface characterization for design of the keyway and a realistic translational failure analysis were not performed. If the first three steps were followed, the excavation plan should have been modified to be compatible with the adverse geologic conditions.

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