Stability of colluvial slopes during earthquakes.

摘要

The stability problems associated with the colluvial slopes are rather common and longstanding in the Greater Cincinnati Area. The basic causes for the development of these slides under static conditions is fairly well understood, and corrective or preventive techniques have been developed and successfully employed. However, the effect of earthquakes on these slopes has not yet been considered and deserves attention. The possibility of catastrophic consequences of seismically-induced landslides in this region is of major concern, and it was the determining factor for undertaking this research study. Therefore, the principal objective of this dissertation was to investigate the effect of earthquakes on slopes consisting of colluvial soils overlying shale, and to determine if the exerted dynamic forces would trigger landslide movements.; Representative composite clay-shale samples, obtained from a typical colluvial hillside in the Greater Cincinnati Area, were tested in a cyclic direct shear apparatus, which was mounted on a frame and attached to the load cell from the MTS piston actuator. The samples were initially consolidated under a selected normal pressure, then sheared either to a predetermined fraction of the strain corresponding to their shear strength, or until their residual strength was developed. Pulsating strains were then superimposed that simulated seismic excitation, and the responses were recorded. The results from the laboratory experiments were then used in the analyses of "infinite colluvial slopes" for a wide variety of assumed conditions.; Generally, the stress-time history diagrams for nearly all the tests followed the same trend, i.e., drops in the magnitude of stresses mobilized during the first few cycles were well pronounced, and these drops diminished gradually during subsequent cycles. Thus, it was concluded that seismic excitation tended to deteriorate the bond at the clay-shale interface of a colluvial slope, with the potential consequences of large and fast slope movements that may continue even after the ground motion ceases.