The Experimental Research And Constitutive Modeling Of Bonding Structured Clay

Bonding structure exists widely in the natural clay.Due to the bonding,natural clay has a higher strength than the reconstituted clay.While the bonding gradually decays with the development of deformation.Thus during the loading,the modulus of the natural clay can firstly be higher than the cooresponding reconstituted clay and finally tend to the reconstituted clay.This phenomenon can not be ignored in the practical engineering,otherwise it may lead to risk.Therefore it is essential to develop a constitutve model to describe the influence of bonding in natural clay.Due to the large dispersions of bonding in natual clays and the changes occurred in the sampling process,the author adopts cmented mud pouring to make the artifical bonding structured clay sample to simulate major characteristics of the natural bonding structured clay.Applying the domestic WG(GDG)high pressure consolidation apparatus and the GDS TTS standard stress path triaxial test apparatus from the United Kingdom,one-dimensional compression tests and drained triaxial compression tests are performed.The test data indicate that:(a)the bonding makes the shearing ultimate stress ratio be higher than the reconstituted clay;(b)the bonding restricts the freely developing of dilatancy.Based on the test results,a dynamic critical state line,named moving critical state line(MCSL),is extended from the traditional static critical state line(CSL)in p?q stress space.MCSL parallels to the CSL and moves to the CSL as bonding decays.Then a new yielding function matching the MCSL is proposed and the dilatancy equation is modified according to the associated flow rule.After that,bonding is added to be considered in the structured UH model.Applying the transformed stress method based on the spatially mobilized plane(SMP),the structured UH model considering bonding is applied to three-dimensional stress states.Compared with the structured UH model,the presented model adds a new model parameter named the initial soil bonding stress s0 which is the initial horizontal distance between MCSL and CSL in p?q stress space.It can be determined through the unconfined compression test.The evolutions of the presented model indicate that the presented model is qualified to smoothly and continuously describe:(a)the isotropic compression behaviors of the bonding structured clays;(b)the characteristics of the ultimate stress ratio in shearing of the bonding structured clays;(c)the dilatancy rule of the bonding structured clays;(d)the influence of stress Lode angle in true triaxial loading of the bonding structured clays.Comparisons between model predictions and test data indicate that the structured UH model considering bonding can reasonably describe behaviors of the bonding structured soils in isotropic compression,one-dimensional compression,drained/undrained triaxial compression,drained shearing with constant p and true triaxial loading.