Change Law In Strength Sensitivity Of Natural Clays With Considering Effects Of Consolidation Stress Paths

Due to the structural and anisotropic properties of natural sedimentary soils during long-term depositional and post-depositional process,the mechanical properties of natural clays must be related to the loading paths.At present,the mechanical behaviour of reconstituted clays are generally used as reference in evaluating the soil structure of natural soils without considering the influence of anisotropic consolidation stress paths.In this thesis,a series of triaxial undrained shear tests under anisotropic consolidation stress paths are performed on different natural structural clays and reconstituted clays,and the intrinsic compression line and intrinsic strength lines of reconstituted clay are introduced to investigate the effect of deviatoric stress on compression and undrained strength behavior.By comparing the different compression and undrained strength behavior of natural clay and reconstituted clay under anisotropic consolidation stress paths,the change law of strength sensitivity of natural clyas are studied.The main studies and conclusions are summarized as follows:1)A series of triaxial undrained shear tests under anisotropic consolidation stress paths were performed on Wenzhou clay reconstituted at two kinds of initial water content.The study found that,the sample drainage volume strain increases with the increase of the consolidation deviatoric stress under anisotropic consolidation under the same mean effective pressure.Thus the sample becomes dense,the soil undrained shear strength increases and the failure pore pressure decreases during undrained shearing.2)A series of triaxial undrained shear tests under anisotropic consolidation stress paths were performed on two kinds of Wenzhou natural clay.The study found that,the undrained shear strength increases slightly with the increase of consolidation press while the consolidation pressure is less than the consolidation yield pressure.When the consolidation pressure exceeds the yield stress,the void ratio after anisotropic consolidation decrease and the undrained shear strength increase with the decrease of effective principal stress ratio(K = ?'3/?'1)under the same mean effective pressure p.3)The compression lines of reconstituted clays obtained from triaxial compression tests under anisotropic consolidation stress paths are normalized by the void index calculated using the measured reconstituted intrinsic parameters through the corresponding triaxial compression test.The study found that,the normalized compression line is consistent with the one-dimensional extended intrinsic compression line EICL.Which means that,the instinct compression line can also apply to the three dimensional axisymmetric stress conditions;4)The relationship between the void index Iv calculated using the measured reconstituted intrinsic parameters and the undrained strength S*u under anisotropic consolidated stress paths could not be normalized to the intrinsic undrained strength line(ISuL)based on the K0 undrained consolidated shear tests of reconstituted clays proposed by Chandler.The study found that,the plot of Iv and S*u with the higher value of the undrained strength ratio(R*su=S*u/p')lies above that with a lower R*su.It is also evidenced from the laboratory tests that the value of R*su increases with the decrease of the effective principal stress ratio K and the initial water content of reconstituted clays;5)The sensitivity framework proposed by Cottechia&Chandler is extended to current stress level state and anisotropic consolidation stress paths.The study found that,the strength sensitivity of natural structural calys exponentially decrease with the increase of mean effective stress.