تخمین پتانسیل روانگرایی خاک با استفاده از سرعت موجی برشی در تهران، ایران Evaluation of liquefaction potential of soil using the shear wave velocity in Tehran, Iran

1. INTRODUCTION Of the several field techniques routinely used to assess triggering of seismic soil liquefaction [standard penetration test (SPT), cone penetration test (CPT), Becker hammer test (BHT), shear-wave velocity (VS)], only the shear-wave velocity test measures a fundamental property of the soil. Nevertheless, liquefaction assessment correlations based on in situ penetration index tests are more widely used in engineering practice to estimate the potential for triggering or initiation of seismicallyinduced soil liquefaction. Compared with VS, SPT and CPT penetration methods have the advantage of correlating more directly with relative density, which has a strong effect on the cyclic behavior of saturated soil (Idriss et al., 2008). In contrast, VS is considerably less sensitive to problems of soil compression and reduced penetration resistance when soil fines are present, compared with SPT and CPT penetration methods. Therefore, VS requires only minor corrections for fines content (FC). Evaluation of the liquefaction resistance of soils is an important step in many geotechnical investigations in earthquake prone regions. The procedure widely used in the United States and throughout much of the world for evaluating soil liquefaction resistance is termed the ‘‘simplified procedure.’’ This simplified procedure was originally developed by Seed et al. (1971) using blow counts from the standard penetration test (SPT) correlated with a parameter called the cyclic stress ratio that represents the cyclic loading on the soil. Since 1971, this procedure has been revised and updated (Seed, 1979; Seed et al., 1982; Seed et al., 1985; Youd et al., 1997). In the mid-1980s, a parallel procedure based on the cone penetration test (CPT) was introduced by Robertson et al. (1985), which also has been revised and updated (Seed et al., 1986; Stark et al., 1995; Olsen, 1997; Robertson et al., 1998). Over the past 20 years, numerous studies have been conducted to investigate the relationship between VS and liquefaction resistance. These studies involved field performance observations (Stokoe et al., 1985; Robertson et al., 1992; Kayen et al., 1992; Andrus et al., 1997), penetration-VS correlations (Seed et al., 1983; Lodge, 1994), analytical investigations (Bierschwale et al., 1984; Stokoe et al., 1988), and laboratory tests (Dobry et al., 1981; De Alba et al., 1984; Tokimatsu et al., 1990). Several of the liquefaction evaluation procedures developed from these studies follow the general format of the Seed-Idriss simplified procedure, where VS is corrected to a reference overburden stress and correlated with the cyclic stress ratio. Nearly all were developed with limited or no field performance data. Some of these procedures follow the general format of Seed-Idriss simplified procedure in which the VS is corrected to a reference vertical stress and correlated with the cyclic stress ratio. This paper presents the results of the comparison between the VS and SPT methods of soil liquefaction potential evaluation in the south-east of Tehran. The liquefaction potential index is also calculated by Iwasaki et al. (1982) procedure for both methods.