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Soil liquefaction and cyclic mobility evaluation for level ground during earthquakes

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    ABSTRACT: Based on existing methods eight common parameters affecting the soil liquefaction are considered and weighted through the principal component analysis. To reduce the dimensionality of the data set, four principal components are obtained by projecting the multivariate data vectors on the space spanned by the eigenvectors. Using the available field liquefaction and non liquefaction data, the influence of various parameters in evaluation model is quantified by golden section search. The field data gathered from the Chi-Chi earthquake of Taiwan in 1999 is also used to perform the verification of evaluation model. The results reveal that the proposed method is simple and effective.
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    ABSTRACT: The Chi-Chi Earthquake induced extensive soil liquefaction in many areas in central Taiwan, and caused substantial damage to buildings, roadways, bridges, and water front structures. Field inves-tigation and explorations were performed in Yuan-Lin and its neigh-boring towns, Da-Chun and Sheh-Tou. Thin-walled tube "undisturbed" soil samples were taken during the subsurface explorations. Labora-tory dynamic tests were conducted on these samples collected by Na-tional Taiwan University and the National Center for Research on Earth-quake Engineering. The liquefaction test results provide the relation between cyclic shear stress ratio and number of stress cycles to initial liquefaction. The stress-strain relations during the stress-controlled and strain-controlled cyclic triaxial tests, and resonant column test re-sults were obtained to study the characteristics of shear modulus and damping of these soils at various strain amplitudes. The results can be used in seismic ground response analysis in the Yuan-Lin area. The stiffness reduction versus pore pressure generation under cyclic load-ing was also studied. The results can be used for the evaluation of the soil-structure interaction and the design of foundations under earth-quake loading.
    Journal- Chinese Institute of Engineers 07/2002; 25(5). · 0.21 Impact Factor
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    ABSTRACT: A series of tests undertaken to investigate the undrained shear behavior of sands with different grading is presented. The tests were conducted by means of a new ring shear apparatus at different relative densities and normal stresses. Silica sands constituted to various uniformity coefficients were classified as well graded (WG), intermediately graded (ING), narrowly graded (NAG) and gap graded (GAG). Results of the investigation show that in medium and dense states the values of their peak strengths are ranked as WG> ING> NAG> GAG. However, their steady state strengths are in the order of NAG> ING>WG>GAG. From the viewpoint of public safety, the narrowly graded sample in medium and dense states has the lowest potential for large travel distances following a slope failure. In loose state however, the narrowly graded specimens readily undergo complete liquefaction, described in this paper as the reduction of steady strength to zero after failure. Although the steady state strengths of WG, ING graded and NAG specimens in loose state are very low, only the steady strengths of NAG and ING specimens have steady state strengths of zero. These results show that while higher uniformity coefficient may equate to or translate into higher peak and higher steady-state strength in soils at a given set of conditions, it might not when the set of conditions are altered; and that under certain circumstances, engineers might want to choose poorly graded soils over better graded ones.