Applicability to Korean Marine Clay of the Mobilized Undrained Vane Shear Strength Using Correction Factors

Abstract

The undrained shear strength normalized by the yield consolidation pressure, su=pc', is presented for four coastal sites: Busan= Gwangyang and Incheon=Gunsan, having the characteristics of high and low plasticity, respectively. The field vane shear strengths, su(FVT), were compared with unconfined compressive strength, qu=2 which has been used as a representative testing method in Korea. Many researchers have suggested that the undrained shear strength normalized by the yield consolidation pressure, su=pc', depends on Ip. However, the undrained shear strength normalized by the yield consolidation pressure, su=pc' is in the range of 0.25-0.35, independently of the plasticity index, Ip except for su=pc' using qu=2 values in the case of soils having a low plasticity, such as Incheon and Gunsan intermediate soils.Bjerrum's correction factor has been commonly applied to evaluate mobilized undrained shear strength using the field vane test in Korea. However, the corrected undrained shear strengths using Bjerrum's correction factor, including Morris and Williams' method, were considerably underestimated for Korean marine clay when compared with the qu=2 values that have been used as the mobilized undrained shear strength for practical design in Korea.

Nonparametric Estimation of Undrained Shear Strength for Normally Consolidated Clays

“…Empirical correlations of the undrained shear strength, usually normalized by the effective overburden pressure ' v , are mostly expressed as a function of a preselected soil index property (e.g., plasticity index) in the form: S u / ' v = C 0 + C 1 (I d ) k , where C 0 and C 1 are constants to be determined from the measurements; k is usually taken as 0.5 or 1; and I d represents the preselected soil index property. In particular, the S u / ' v -PI correlations (i.e., the relationships between the normalized undrained shear strength and the plasticity index PI) proposed by Skempton (1957) and Bjerrum and Simons (1960) are the most commonly used in engineering practice (Yin et al 2003;Kim et al 2013). They are particularly useful for the verification of the initial strength deduced from site characterization program and for the feasibility studies during preliminary geotechnical design.…”