Characteristics of Vertical Ground Motions Recorded During the Lorna Prieta Earthquake

A study of a limited number of vertical ground motion acceleration-time histories recorded during the Loma Prieta earthquake of October 17, 1989 has been made. It has been found that maximum vertical ground motions may be greater than the horizontal ground motions in the near vicinity of the fault rupture zone. The limited records suggest that there is more spectral energy at very short structural periods in the vertical ground motions as compared with the horizontal ground motions. At longer periods, the vertical energy is significantly less, however, there is an increasing trend for very long structural periods

Investigation of Ground Cracking at the Van Gogh Street School, Granada Hills, California

The Van Gogh Street School, located in the northern portion of the San Fernando Valley in the City of Los Angeles, suffered damage from the January 17, 1994 Northridge earthquake having a moment magnitude of 6.7. The school experienced significant cracking in some of the building walls and asphalt paving. The school, located approximately 7 miles from the epicenter, was within a zone of surface cracking coincident with the east-northeast to northeast trending Mission Hills syncline. There was speculation that either fault rupture, liquefaction and/or seismic settlement may have occurred at the school site. A geotechnical investigation was performed to evaluate the ground cracking at the school. The comprehensive exploratory program consisted of mapping and shallow trenching of the surface cracks, closely spaced cone penetration tests (CPTs} and borings to characterize the stratigraphy of the underlying alluvial materials, and high resolution seismic reflection surveys to map the underlying geologic structure and determine if faults were present within the bedrock. This combination of exploratory tools was utilized simultaneously to provide the necessary data to accurately evaluate the shallow and deep structural and stratigraphic conditions beneath the school site

Case History of Seismic Base Isolation of a Building –The Foothill Communities Law and Justice Center

The Foothill Communities Law and Justice Center, located in seismically active Southern California, is the first building in the United States to be base isolated for seismic resistance. Natural rubber isolators with layers of steel plates were used to make the fundamental period of vibration of the base isolated building about twice as long as that for a comparable conventional fixed base building. Most earthquake energy is present in the shorter period ranges, and at longer periods, a building should be subjected to less earthquake input; this will allow buildings to be designed more economically and increase the likelihood of less damage, both structural and non- structural. The experience of the Law and Justice Center after three small earthquakes suggest that the concept is not only feasible, but may be the wave of the future for what would be relatively short period buildings

Performance of Shored Earth Retaining Systems During the January 17, 1994, Northridge Earthquake

The performance of several temporary deep shored earth retaining systems during the January 17, 1994 Northridge earthquake in Southern California is documented. These shoring systems ranged from 30 to 70 feet in depth and were subjected to severe ground motions with little deflection or distress

Settlement of Shallow Foundations Constructed over Reinforced Soil: Design Estimates vs. Measurements

Faced with difficult soil conditions for the support of two 6-story office towers in Dublin, CA and of a 6-story parking garage in Sacramento, CA, engineers recommended the use of Geopier Rammed Aggregate Piers to reinforce the soil for the support of high bearing capacity spread footings instead of deep foundations. Foundation selection for both sites was influenced by long-term settlement performance, schedule and cost savings, and seismic uplift resistance. Rammed aggregate piers were installed to strengthen upper weak and compressible soil layers resulting in a substantially stiffer soil layer on which shallow, high bearing capacity spread footings were constructed. Several rammed aggregate piers were also installed with steel anchors to resist seismically induced overturning forces. Design parameter values were confirmed by full scale aggregate pier modulus tests and uplift tests and a 24 hour load test at the Dublin site. Total settlements were estimated to be less than 1½ inches for the Sacramento site and less than 1 inch for the Dublin site. Measured settlements are less than 1 inches total for both projects with differential settlements less than ½ inches, confirming the design approaches and soil properties used for design. Site selection, rammed aggregate pier design methodology, modulus and uplift load test results, and measured settlement performance are presented for two projects in California

Osterberg Load Cell Testing of a Deep Reinforced Concrete Pile

A pedestrian bridge was constructed between two portions of a hospital in Southern California. Potentially liquefiable soils were present to a depth of about 72 feet below the ground surface. Because of the liquefiable soils, the bridge was to be supported on 30- inch-diameter cast-in-place piles drilled to a depth of approximately 90 feet below the ground surface. A test pile was constructed to confirm the soil capacities for the bridge. An Osterberg Load cell (O-cell) was placed near the middle of the test pile, and the downward load capacities of the deeper soils (below the elevation of potentially liquefiable soils) were tested using the upper portion of the pile to provide reaction. Instrumentation of the test pile consisted of four pairs of vibrating wire strain gages mounted on the pile reinforcing cage at four depths. The strain gages were connected to a data acquisition unit used to record data during the pile load test. A pair of tell-tale rods connected to electronic dial gages monitored the movement of the lower plate of the O-cell. Another pair of tell-tale rods was used to monitor the movement of the top of pile during the test while a third pair of tell-tale rods was used to monitor the compression of the upper portion of the pile. The pile load test was successful in confirming the predicted pile capacities, and the production piles were installed. The Osterberg Load cell was an economical method of testing the pile for this particular application

Investigation of Sanitary Landfill Slope Performance During Strong Ground Motion from the Loma Prieta Earthquake of October 17, 1989

This paper evaluates the performance of landfill slopes (refuse fill slopes) during strong ground motion from the October 17, 1989 Loma Prieta Earthquake (M7.1) that affected the Santa Cruz Mountains - San Francisco Bay region. The earthquake\u27s occurrence in a highly populated area that contains the waste disposal sites for this large population offered a unique opportunity to review the performance of slopes on the landfills. Current state and federal regulations require the analysis of stability of landfills under seismic loading. To date, these evaluations have relied on gross simplified assumptions. This paper examines whether these assumptions are reasonably correct. There are approximately 35 active landfills in the seven counties surrounding the epicentral area. The landfills are underlain by a variety of geologic materials ranging from Bay Mud (soft sediments) to hard rock. Fill slopes at the landfills range from a few feet to 250 feet high with inclinations as steep as 2:1 (horizontal to vertical). Contact with operators and regulatory agencies indicate that there was very little damage to landfill slopes during the earthquake. The probable ground accelerations at the landfills during the earthquake are estimated based on comparison with accelerations recorded at nearby CSMIP stations or USGS strong motion stations and the site geologic conditions

Correlations of Seismic Velocity with Depth

Correlations of seismic velocity have been made with depth for various geotechnical classifications of soil and rock described. The seismic velocities have been found to be dependent upon geologic age, gravel content, water table depth, dry density and depth of overburden