FLOW SLIDE FAILURES ASSOCIATED WITH LOW LEVEL VIBRATIONS (LIQUEFACTION, LABORATORY TESTING, CASE HISTORIES, LOOSE SANDS, ANALYSIS, CALIFORNIA).

摘要

There have been a number of landslides reported in the technical literature which were associated with low level, non-seismic vibratory loads such as trains, blasting and pile driving. These landslides exhibited many of the characteristics of flow slides and occurred in loose, saturated cohesionless soil deposits or in other soils known to contain saturated seams and lenses of cohesionless material. The aims of this study were: (1) To determine the conditions under which saturated cohesionless soil could be made to flow, and (2) To determine whether this type of behavior could be predicted from the back calculations of two documented flow slide failures.;Soil response to undrained loading conditions was found to be either contractive in loose samples or dilative in denser samples. In tests on loose sand samples (D(,r) = 35%) subjected to either cyclic or monotonic loading, collapse-type failures occurred in which both the axial strain and pore pressure would increase rapidly (usually in less than 0.5 seconds) as the effective stress reduced to a low value. This type of failure could be responsible for the kind of soil behavior associated with flow slides.;In cyclic tests on denser sand samples (D(,r) = 55%) collapse type failure did not occur. Instead cyclic strains accumulated indefinitely with each cycle of stress and it was necessary to use a definition of failure in terms of limiting axial strain.;Two flow slide failures in railroad embankments were analyzed using the results of the laboratory investigation. Analysis of a failure in the San Francisco Bay Area indicated that a large zone of soil liquefied, which would have resulted in a downstream slope failure similar to that which was observed. The failure at Cajon Pass is known to have occurred on the plane of contact between the old and the new railroad embankments. Although analysis of this plane resulted in a zone of liquefaction caused by the train loading which would not have resulted in instability, a progressive liquefaction analysis indicated eventual failure of the embankment.;Series of anisotropically consolidated undrained (ACU) triaxial tests were conducted on samples of Sacramento River Fine Sand, a clean uniform alluvial sand. A total of 141 triaxial tests were performed in a 2.8 inch diameter triaxial apparatus.