INTELLECTUAL MERIT: Many of the commonly used procedures for evaluating liquefaction are largely based on field and laboratory testing of clean sands or sands with a limited amount of fines. For example, the liquefaction-triggering database of the well-used Seed et al. (1985) SPT-based correlation contains only 13 cases involving soils with significant fines (i.e. > 35% fines). The state-of-the-art lique-faction evaluation paper by Youd et al. (2001) and design guidelines commonly use the "Chinese Criteria" for identifying soils susceptible to liquefaction. For example, "Guidelines for Analyzing and Mitigating Lique-faction Hazards in California" (Martin and Lew 1999) states, "clayey soils are those that have clay contents (particle size <0.005 mm) greater than 15 percent," and "If clayey soil materials are encountered during site ex-ploration, those materials may be considered non-liquefiable."
However, research following recent earthquakes has identified a large number of cases where ground failure in fine-grained soils containing more than 15% clay-size particles caused significant building damage. For example, Bray et al. (2001) found that liquefaction and ground softening in the silts of Adapazari, Turkey were responsible for much of the damage observed in this city. These silty soils typically had clay contents greater than 15%. Recently completed cyclic triaxial testing of carefully retrieved soil specimens from Ada-pazari (Bray et al. 2004) confirm that low plasticity silts with high clay contents can liquefy under severe seis-mic loading. The response of these soils is less understood than that of clean sands. This research is ena-bling a much-needed re-evaluation of the liquefaction susceptibility of silty and clayey soils and provid-ing insight regarding the dynamic response of fine-grained soils based on their mineralogy.
The primary goal of this study is to assess the cyclic response of soils with significant fines (both plastic and non-plastic). The advanced cyclic testing of these soils is required to characterize the liquefac-tion susceptibility of fine-grained soils, to evaluate their liquefaction resistance, and to gain insight regard-ing their post-liquefaction response (i.e. volumetric strain and residual strength). Cyclic simple shear test-ing, with some complementary cyclic torsional shear and cyclic triaxial testing for comparison, are being performed on the silty and clayey soils that were previously retrieved from Adapazari, Turkey. These soils possess a range of soil characteristics that represent many fine-grained soils in the United States.
Specimens are being prepared in a uniform manner using wet-pluviation so that the specimen re-sponse reflects that of soils deposited in nature but without the inherent variability of natural soil deposits. With fairly uniform soil specimens, important effects that could not be isolated by testing "undisturbed" specimens of natural soils, such as the effects of soil plasticity, void ratio, confining stress, initial static driving stress, overconsolidation ratio, and time under confinement, can be systematically evaluated. The results of this program of cyclic testing will help redefine the liquefaction susceptibility of fine-grained soils. The screening for soils susceptible to liquefaction is the first step in evaluating the hazards associated with liquefaction. Preliminary findings from field observations from recent earthquakes and re-sults from tests on "undisturbed" specimens of fine-grained soils indicate that the engineering profession is currently classifying soils that are susceptible to liquefaction as "non-liquefiable."
BROADER IMPACTS: The implementation of California's Seismic Hazards Mapping Act and other related efforts are largely based on empirical methods that require re-evaluation and updating as important case histories emerge, such as the devastation of buildings in Adapazari, Turkey due to liquefaction and softening of silty and clayey soils. Critical lessons can be learned from this study, because the soils and intense level of earthquake shaking investigated in this research project represent one of the controlling earthquake hazards in the U.S. (i.e. poor soils close to large magnitude earthquakes). The responses of non-plastic silts and slightly plastic clayey silts are significantly less understood than that of clean sands, and the liquefaction-triggering database contains relatively few case histories involving soils with signifi-cant fines. This research allows for a re-evaluation of the state-of-the practice "Chinese criteria" for de-termining the liquefaction susceptibility for silty and clayey soils (readopted by Youd et al. 2001). It also complements numerous previous field, laboratory, and analytical studies of liquefaction triggering and the consequences of liquefaction, e.g. ground failure and its effects on structures.
