Abstract: Site investigations on the decay characteristics of the soil shear modulus have so far been very limited. Meanwhile, for the laboratory experiments, which may need sampling, transportation and other procedures, soil samples are normally disturbed to some extent. However, accurate descriptions of the soil modulus are important for the site evaluations as well as the structure designs. Therefore, a series of self-boring pressuremeter based in-situ tests with a maximum depth of 33m has been carried out in the lacustrine clay of Taihu tunnel area, China. Total stress-strain curves of the different soils were obtained, and on basis of that, the shear modulus decay characteristics of the soils were analyzed in detail. Shear modulus distribution along the depth was discussed under different shear strains, where a common conclusion could be obtained for different soils is that strong degradation characteristics are shown for the small strains, and then would become stable gradually as the strain increases. A correlation law between shear modulus as well as its decay characteristics and plasticity index was established. Results show that the plasticity index can be used as a reliable index to evaluate the shear modulus decay characteristics of soils.

Key words: self-boring pressuremeter test, lacustrine clay, undrained shear strength, shear modulus, degradation characteristics