Mechanics of the Lone Mountain landslides, San Francisco, California

Abstract

This study was initiated for the purpose of determining the mechanics and causes of three landslides that had occurred on Lone Mountain. A careful survey was made of the geology at the slide localities. By means of graphical methods based on the principles of soil mechanics, the frictional resistance to sliding, which the ground exerted when motion impended, was determined. The inherent frictional properties of the ground were evaluated by laboratory experiments on samples of material obtained from the slide localities. Discordance between the graphical and the experimental values for the friction coefficients points to the presence of an agent which nullified, in part, the action of friction. The natural stability of the hillside on which the Parker Avenue slide occurred was reduced through a series of civic improvements which, in combination with the unfavorable geologic structure and the presence of water, ultimately caused tile landslide. The two smaller slides along Turk Street may be attributed to the hydro-dynamic action of water in the highly porous and unconsolidated sandy ground, with the consequent reduction of friction between the sand grains, and resultant liquefaction of the hillside mass.