Informe licuacion

Characterization of Liquefaction Resistance in Gravelly Soil : Large Hammer Penetration Test and Shear Wave Velocity Approach
Ping-Sien Lin*,1, Chi-Wen Chang1, Wen-Jong Chang2
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Department of Civil Engineering, National Chung-Hsing University Taichung, Taiwan, 402, ROC Ph: (04) 2287-2221 ext 229; Fax: (04) 2286-2857 E-mail: pslin@dragon.nchu.edu.tw (Lin)

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Department of CivilEngineering, National Chi Nan University, Puli, Taiwan. 545

ABSTRACT

Gravelly soil is generally recognized to have no liquefaction potential. However, liquefaction cases are reported in central Taiwan in 1999 Chi-Chi Taiwan earthquake and in 1988 Armenia earthquake. Thus, further studies on the liquefaction potential of gravelly soil are warrent. Because large particles can impede the

penetrationof both SPT and CPT, shear wave velocity based correlation and large Hammer Penetration Test (LPT) are employed to evaluate the liquefaction resistance of gravelly soils. A liquefied gravelly deposit site during the Chi-Chi earthquake

was selected for this research. In situ physical properties of soil deposits are collected from exploratory trenches. Instrumented Large Hammer Penetration Test(LPT) and shear wave velocity (Vs) measurements were performed to evaluate the liquefaction resistance. In addition, large-scale cyclic triaxial test on remolded gravelly soil samples (15 cm in diameter, 30 cm in height) were conducted to verify and improve LPT-based and Vs– based correlations. The results show that the Large Hammer Penetration Test and shear wave velocity methods are reasonablysuitable for liquefaction assessment of gravelly soils.

Keywords: Gravelly soil, Liquefaction, Large Hammer Penetration Test, Shear wave velocity

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INTRODUCTION

Soil liquefactions had been observed in central Taiwan area after 1999 Chi-Chi Earthquake (Mw=7.6). Although after earthquake investigations reveals that most liquefaction in Chi-Chi earthquake occurred in alluvium layers,which are composed of fine sand or fine sandy silt, liquefaction cases of gravelly soils were also reported in the Wufeng and Nantou Area. Gravelly soil is generally recognized to have no

liquefaction potential. The reported cases of liquefied gravelly deposits in 1999 Chi-Chi Earthquake (Chu et al. [1]) and in 1988 Armenia earthquake (Yegian et al. [2]) raise concerns of liquefaction insaturated gravelly soils. Because there are very few

well-documented case histories of liquefied gravelly deposits, research in studying the liquefaction mechanism and developing proper analyzing techniques for gravelly soils is warranted to minimize damage and loss caused by liquefaction of saturated gravelly soils. Because the composition and fabric of gravelly deposits is different from otheralluvium deposits, evaluation methods developed for sandy soils need be critically reviewed and modified to apply in gravelly soils. Currently, there is no

well-recognized method for assessing the liquefaction resistance of gravelly soils. The conventional methods for evaluation of liquefaction resistance can be divided into two groups: (1) laboratory cyclic liquefaction tests (ex. Seed and Lee[3]), and (2) semi-empirical correlations with various in situ tests (ex. Seed et al. [4], Robertson and Wride [5], Andrus and Stokoe [6], Harder [7]). The oversize of gravelly

particles makes cyclic triaxial testing apparatus with conventional specimen size not appropriate to gravelly soils. Additionally, conventional sampling techniques are not

able to retrieve undisturbed, saturated,gravelly specimens. Large-scale cyclic triaxial testing apparatus with specimen diameter 150 mm is setup to performed series cyclic liquefaction tests in reconstituted gravelly specimens. Also, internal shear wave

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velocity measurement system is integrated to the large-scale cyclic triaxial apparatus to measure the initial shear wave velocity of reconstituted specimens. The developed system is...