Abstract:

Gassy soft soil is widely distributed in five continents in the world. The existence of a large number of discrete bubbles can strengthen or damage the undrained shear strength of soft soil. However, there is still a lack of analytical expression for undrained shear strength of gassy soil, which can comprehensively consider the competition mechanism between gas-phase strengthening and gas-phase damage. Combined with the theory of critical state soil mechanics and based on the yield function of gassy soil proposed by the author, this paper established the mathematical relationship between the intercept of critical state line and the gassy characteristics (u _{w 0},y ₀)  of soil in the  v-lnp¢  space, and then deduced the theoretical expression of undrained shear strength s_u of gassy soft soil in triaxial stress state. At the same time, using the deduced theoretical calculation formula of undrained shear strength of gassy soft soil, this paper compared the theoretical predictions and test results of undrained shear strength for three kinds of typical gassy soft soil under different gassy characteristics, including Malaysian kaolin silt, Combwich mud and kaolin clay. In addition, this study analyzed the predicted error percentage of four different theoretical calculation models for undrained shear strength of gassy soft soil, proving the rationality of the theoretical calculation formula of undrained shear strength based on the improved constitutive model of gassy soft soil. The proposed model can more accurately consider the dual effects of gas phase strengthening and gas phase damage of gassy soft soil simultaneously.

Key words: gassy soft soil, undrained shear strength, yield function, gas phase effect