LIQUEFACTION HAZARDS AND THEIR EFFECTS ON BURIED PIPELINES. TECHNICAL REPORT

The research described in this work involves the evaluation of liquefaction-induced ground movements and their effects on buried pipelines. The work is divided into three components: 1) review of liquefaction phenomena and associated ground displacements, 2) characterization of liquefaction-induced lateral spreading through observations and measurements of lateral spread deformations during past earthquakes, and 3) parametric study to evaluate buried pipeline response as a function of soil properties and geometric characteristics of lateral spreads. Case studies of four earthquakes were reviewed in which occurrences of lateral spreading have been reported. These include the 1906 San Francisco, 1964 Alaska, 1971 San Fernando, and 1983 Nihonkai-Chubu earthquakes. From these case studies, the geologic and morphologic features which control the displacement patterns of lateral spreads are identified. The damage caused by lateral spreading to lifeline system, and pipeline networks in particular, are examined. A detailed investigation was performed of ground movements associated with the 1906 San Francisco earthquake. The direction and magnitude of soil deformations are plotted on the city street system, using as references both historical accounts and photographs of damaged parts of the city after the earthquake. The pattern of soil movements are related to former topographical features of the region, the location and nature of filled areas, and the location of breaks in the pipeline system. Displacement patterns typical of those observed during the 1906 San Francisco earthquake were used as a basis for a parametric study of buried pipeline response to lateral spreading. The soil/pipeline interaction was analyzed by means of a special computer code, UNIPIP, which is capable of evaluating the elasto-plastic behavior of both the soil and the pipeline material well into the post-yield range. The strains and deformation of a 610-mm-diameter continuous steel pipeline were evaluated as a function of the maximum displacement of a lateral spread, the width over which the maximum displacement develops, and the shear strength and density of the surrounding soil.