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Shi J.,Institution of Engineering Mechanics
Applied Mechanics and Materials | Year: 2011

Based on liquefaction survey of 2003 Xinjiang Bachu earthquake of Ms6.8 and in-situ shear wave velocity testing data, the feasibility and applicability of five typical liquefaction evaluation methods which use shear wave velocities as criteria are presented herein. Analysis showed that none of the five liquefaction evaluation methods can provide a satisfactory result in Bachu area. The successful judging rates are only 36% to 64%. The intensity method which is employed to evaluate liquefied and non-liquefied sites in Bachu area provides only 40% successful judging rate, and the method is risky in intensity VII area and conservative in intensity IX area. The critical lines of the five methods deviate greatly from the actual lines. in intensity VII area all the five methods incorrectly misjudge. Further work has to be conducted to research on the soil properties in Bachu area and to establish the regional liquefaction evaluation method in Xinjiang. © (2011) Trans Tech Publications.

Sun R.,Institution of Engineering Mechanics | Sun R.,Harbin Engineering University | Chen H.-J.,Beijing University of Technology | Yuan X.-M.,Institution of Engineering Mechanics
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2010

By using the test data, the uncertainty of the dynamic modular ratio G/Gmax and damping ratio λ versus dynamic shear strain γ for the conventional soils in China is studied. The characteristics of the uncertainty distribution, the probability indexes as well as the range of G/Gmax and λ for the typical strains under different probabilities are presented. Based on 588 groups of test results from 42 cities and districts in 17 provinces in China, the uncertainty of the modular ratio and damping ratio versus 8 typical shear strains is analyzed. The results indicate that most of the uncertainty distribution of G/Gmax and λ is abnormal and that the statistic indexes for the probability are regular. The standard deviation and the variation coefficient of G/Gmax and λ are both significant, and meanwhile the maximum of the standard deviation just appears in the sensitive range for the seismic analysis of soil layers. The 95% reference values of G/Gmax and λ are quite different from the envelopes of G/Gmax and λ for all types of soils. The variation coefficients of G/Gmax increase with the increase of the shear strain, but the variation coefficients of λ decrease with the increase of the shear strain. The uncertainty of G/Gmax is obvious at the large strain, while that of λ is obvious at the small strain. The variation coefficients of λ are larger than those of G/Gmax, indicating the uncertainty of the dynamic damping is more remarkable than the dynamic modulus.

Yuan X.-M.,Institution of Engineering Mechanics | Cao Z.-Z.,Institution of Engineering Mechanics
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2011

The liquefaction behaviors in the great Wenchuan 8.0 Earthquake in 2008 are quite notable, and the liquefaction of gravel soil is significant. Considering the wide distribution of gravel soil in some places in China, the liquefaction prediction methods should be developed. The existing methods for evaluating the liquefaction of sand soil result from the sand liquefaction cases, however, SPT technique can not be conducted in the gravel soil layers, and as a result, the existing code is not suitable for the liquefaction assessment of gravel soil. After the investigation for the liquefaction-induced damages in the great Wenchuan Earthquake and in-situ tests for the liquefied and non-liquefied sites, the liquefaction prediction method of gravel soil based on DPT, i. e., the dynamic penetration tests, is presented, and the corresponding model and formula are obtained. The analytical results indicate the liquefaction discrimination of the gravel soil can be divided into two steps, the initial discrimination and the second discrimination. In the initial step, the impossible liquefaction cases are selected, and in the second, the calculation model is adopted by using N 120 as the basic index from DPT. The geological ages, buried condition of the gravel soil layer and gravel contents of gravel soils are considered in the initial discrimination. In the second discrimination, five parameters including the reference value of N 120, gravel content of gravel soils, depth of gravel soils, water table and seismic intensity are concerned. Considering the wide range of liquefied soil depths and its water levels, the reference value of N 120 is deduced by the normalization method and the influence coefficients of the gravel soil depths and the water levels are obtained by the optimal method. The effect of various factors on liquefaction possibility of gravel soil is considered in the present method and the advantages of the model and formula for the second discrimination are noticed by clear expression, high success ratio of regression discrimination, good connection with the past work and convenience in engineering application.

Cao Z.-Z.,Institution of Engineering Mechanics | Cao Z.-Z.,Harbin Institute of Technology | Li Y.-R.,Hebei University of Technology | Xu X.-Y.,Harbin Institute of Technology | And 2 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2012

The serious damage in Songbai village, Deyang, located at the boundary of seismic intensity zone VII and VIII, is induced significantly by liquefaction following the 2008 Wenchuan Earthquake. The large amount of spouted soils categories, a lot of liquefaction-generated ground fissures and the apparent liquefaction-aggravated damage are the typical features and are worth for further study. The detailed in-situ tests and comparison with the previous liquefaction-induced damage reveal: (1) The actual liquefied soils are gravels and significantly different from the spouted deposits, while most of which are medium and coarse sand. (2) An efficacious filed test method for measuring gravel liquefaction resistance has not been proposed ever before. The Chinese dynamic penetration test (DPT) is strongly recommended for gravel liquefaction evaluation for its simple apparatus, economical test, continuous data acquisition, etc. (3) The abundant ground fissures in Songbai village are generated by gravel liquefaction rather than the raptures or secondary faults. The fundamental conditions for the generation of ground fissures by liquefaction are the flat ground surface (slop less than 3%) and horizontal non-uniform distribution of liquefiable soils. (4) The fundamental conditions for seismic damage mitigation by liquefaction are the thick upper non-liquefiable soils and relativey dense upper non-liquefiable soil cap. The corresponding quantitative assessment method needs to be further studied.

Cao Z.-Z.,Institution of Engineering Mechanics | Xu X.-Y.,Harbin Institute of Technology | Leslie Youd T.,Brigham Young University | Yuan X.-M.,Institution of Engineering Mechanics
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2011

The liquefaction-induced damage of Banqiao School building following the 2008 Wenchuan Ms 8.0 Earthquake is typical, and the correlation between the ground fissures and the liquefaction is identified and mechanisms of the building damages as well as the characters of liquefied soils are investigated by field investigation and in-situ tests, such as multi-channels electric resistance test, spectral analysis of surface wave (SASW), dynamic penetration tests (DPT), borehole and trench, etc. The results show that: (1) the ground fissures are generated by the liquefaction rather than the secondary faults and ruptures; (2) Banqiao School building suffered more severe damages than its surrounding buildings from the liquefaction rather than inertia force of shaking during the Earthquake; (3) the subsurface liquefied soils are gravelly soils at the depth of 3.0-6.1 m, which is different from the spouted fine sands; (4) the current knowledge is not true that the gravels are regarded as non-liquefiable soils, and a new procedure for liquefaction evaluation of gravelly soils is demanded.

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