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Introduction to soil engineering
Published in J.A.R. Ortigao, Soil Mechanics in the Light of Critical State Theories, 2020
Soft marine and deltaic clays are common deposits in many countries, e.g., the San Francisco bay mud in the USA, the Osaka bay clay in Japan and the Fraser river deposits in Vancouver, Canada. figure 1.14 presents typical data on the Rio de Janeiro marine clay that covers Guanabara bay. Atterberg limits, in situ void ratios, total unit weights have been plotted, as well as the undrained shear strength cu that will only be discussed later on in chapter 12. Typical average values for this clay are: PL = 40%, LL = 120%, hence PI= 80%. A plasticity index of 80 % is a very large value. The water content is greater than LL, therefore the liquidity index is higher than 1. The in situ void ratio e is typically 4 on the top of the clay layer, decreasing to 3 at the bottom. The unit weight y varies between 13 to 14 kN/m3.
Engineering Seismology Overview
Published in Hector Estrada, Luke S. Lee, Introduction to Earthquake Engineering, 2017
During the 1989 Loma Prieta earthquake, the San Francisco Bay Area (some 100 km north of the epicenter) experienced more damage than the epicentral region. The reason for the extensive damage along the margins of the bay is because of the amplification of the PGA at soft-soil sites. The bay basin is filled with an alluvial soil deposit of silts and clays, along with some layers of sandy and gravelly soils. The upper deposit, or young mud, is composed of silty clay, known as San Francisco Bay Mud. This material is of loose-to-medium density, and very compressible. As shown in Figure 2.9, the ground stratum in the vicinity of the bay is divided into three zones based on underlying material seismic response, from soft mud to hard rock. From Figure 2.9, it is clear that the attenuation of seismic waves varied considerably in different regions of the bay due to the varying subsurface soil conditions. The rock material attenuated the seismic waves relatively quickly compared to the soft young bay mud found at the margins of the bay. The areas underlain by this bay mud experienced the most damage because the soft mud greatly amplified ground motions.
Measured end resistance of CFA and drilled displacement piles in San Francisco Area alluvial clay
Published in DFI Journal - The Journal of the Deep Foundations Institute, 2018
T. C. Siegel, T. J. Day, B. Turner, P. Faust
The subject load tests are all located in the San Francisco Bay Area which is recognised as part of Coastal Ranges geomorphic province. The Coastal Ranges are a series of alternating parallel mountain ranges and valleys trending from the southeast to the northwest along the coast of California that were formed when the Pacific Plate collided with the North American Continental Plate. During the last Ice age (Pleistocene epoch), the sea level was much lower than today, and the current San Francisco Bay Area was a series of broad valleys between the Coastal Ranges. At the beginning of the Holocene epoch, glaciers melted causing a rapid rise in sea level. The resulting influx of seawater through the Golden Gate filled the current San Francisco Bay. As inflow of sea water slowed, the rivers draining into the San Francisco Bay Area continued to deposit material derived from the Coastal Ranges. These youngest Holocene marine sediments continue to accumulate and are recognised as the Bay Muds. The clay that is the subject of this paper is Pleistocene alluvium deposited in the Coastal Range valleys outside the extent of the current San Francisco Bay before the end of the last Ice age. A detailed description of the geologic history of the San Francisco Bay Area is presented by Helley, Lajoie, Spangle and Blair (1979).