Experimental Study On Characteristics Of K₀-consolidated Stiff Clay Under Traffic Loading Conditions

The service performance and operating life of transportation facilities are directly related to the mechanical properties of subgrade soil under traffic loading.Fully understanding the dynamic characteristics and accurately predicting the cumulative settlement of subgrade soils under traffic loading are essential for such engineering applications.It is widely used to study the dynamic response of soil under cyclic loading through laboratory tests.In this regard,there has been a lot of research on sand,silt and soft clay.However,there is very little research on the dynamic response of stiff clay with K0>1 under traffic loading.In this study,a series of traffic loading undrained tests with large number of cycles were conducted on the intact Ko-consolidated Gault and Kimmeridge stiff clays through dynamic triaxial test system(DYNTTS)and hollow cylinder apparatus(HCA).The detailed research contents are as follow:1.One-way cyclic triaxial tests under different cyclic stress ratio have been conducted on Gault and Kimmeridge clays to investigated the cumulative strain,pore pressure evolution,stress-strain hysteresis loops and resilient modulus degradation under large number of cycles.The strain rate and cumulative strain of stiff clay gradually increased with the increase of CSR.With increasing cyclic stress ratio,the cyclic deformation responses can be categorized into stable,metastable,and unstable patterns.Compared with soft clay,the cumulative strain of stiff clay under traffic loading is smaller.However,stiff clay has strong brittleness comparing with soft clay.2.Experimental researches under different cyclic stress ratio have been conducted on Gault and Kimmeridge clays by GDS hollow cylinder apparatus to simulation the characteristic of principal stress axis rotation(PSR)under traffic loading.The influence of PSR on the dynamic characteristics of stiff clay is studied comparing with the results of the cyclic triaxial tests.Results show that under the condition with continuous rotation of principle stress axis,the axial strain of stiff clay is gradually accumulated on the extension side,and its resilient modulus is rapidly degraded.The stiff clay will fail in the most vulnerable direction,that is af=67°,when the CSR is large enough.3.To study the post-cyclic behavior of Gault clay,the standard triaxial compression tests have been conducted on the Gault samples that didn't fail on the cyclic tests.Results show that the post-cyclic strength of samples appears to be not affected by the previous cyclic triaxial loadings but is related to the degree of soil fissure development.However,with increasing CSR in the previous cyclic torsional shear loading,the post-cyclic strength of samples decreased with the increase of CSR.