Study on Strength Criterion of Intact Soft Clay after Monotonic Principal Stress Rotation
Underestimating the influence of principal stress rotation on the foundation soil during the construction is the cause of some engineering accidents. Series of experiments were done to study the strength characteristics of intact soft clay after undrained
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STUDY ON STRENGTH CRITERION OF INTACT SOFT CLAY AFTER MONOTONIC PRINCIPAL STRESS ROTATION Yang Shen Key Laboratory ofMinistry ofEducation for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098, China Geotechnical Research Institute, Hohai University, Nanjing 210098, China Jian Zhou, Xiaonan Gong Institute ofGeotechnical Engineering, Zhejiang University, 20 Yugu Road Hangzhou 310027, China HanlongLiu Key Laboratory ofMinistry ofEducation for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098, China Geotechnical Research Institute, Hohai University, Nanjing 210098, China Underestimating the influence of principal stress rotation on the foundation soil during the construction is the cause of some engineering accidents. Series of experiments were done to study the strength characteristics ofintact soft clay after undrained monotonic principal stress rotation. It was found that compared with the progress of undrained monotonic principal stress rotation, the principal stress direction when samples failed influenced the soils' strength much more obviously. But the pore water pressure generated in the tests including principal stress rotation was much higher than that in the test of fixed principal stress direction shear. It was due to the shearing contraction of intact soft clay caused by principal stress rotation. A modified Lade-Duncan failure criterion was used to normalize these testing results and unify the soil's failure criterion including principal stress rotation. It showed that initial anisotropy was one of the most important determinate factors of intact clay's strength when principal stress rotation occurred during the construction.
INTRODUCTION In the practical issues soil would undergo complex stress path. Monotonic principal stress rotation will occur as a kind of typical path when the foundation is subject to filling dams, excavation or some other constructions. It, coupled with soils' anisotropy, may influence soils' strength properties. And such influence would be amplified with the scale of construction expanding. So underestimating these influence will have grave consequences. Laboratory experiment is one of the methods to evaluate these effects properly. Several researchers like Arthur et al. (1979), Hight et al. (1983), Symes et al. (1984,1988), Wijewickreme and Vaid (1993), Zdravkovic and Jardine (2001), Sivathayalan and Vaid
(2002), Han and Penumadu (2005) have done tests to study the soil's properties under principal stress rotation. But most samples tested before were remoulded silt or sand. Compared with them, clay, especially intact clay, may show quite different reaction on principal stress rotation because of its structural property, anisotropy and other characteristics. So the authors did a series of intact clay experiments to study the influence of principal stress rotation on its strength. How to generalize the strength criterion for such stress path is also discussed. SOIL PROPERTIES AND TESTING PROCEDURES
The soil tested was a kind of typi
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