| Soft clay has a high compressity and distinctive rheological characteristic, if the creepunable to reach a stable state, the regular service of constructions built on that is seriouslythreatened. With the rapaid development of economy in soft clay regions, lots of hugeconstructions are under constructing, the creep characteristic and the long term stability of thefoundation attracted the general concern. Previous researches have verified that bond water isthe main factor of creep characteristic of soft clay, and the bond water largely embodies howthe material composition influenced the creep characteristic of soft clay. In this paper, study ofcreep and long term strength characteristic of soft clay is carried out in perspective from thebond water, which is of a great theoretical and practical value.The deltaic soft clay of Shanghai, littoral soft clay of Tianjin and lacustrine soft clay ofSuzhou is taken as the reseearch object. Based on the previous researches and theories ofengineering geology, foundation soil science, soil mechanic and clay mineralogy, tested thematerial composition, physical-mechanical property and the creep characteristic of the soft clay,analysised the microstructure of the soft clay before and after the creep test, and comparativeanalysised the creep characteristic of the three kind of soft clay in perspective from the bondwater. Tested the bond water content and classified the type of the bond wter, accordinglycarried out a seris of creep test on remolded soft clay, studied the influence mechanism of bondwater on creep characteristic of soft clay, and the quantitative relationship between bond watercontent and secondary consolidation coefficient, viscisoty coefficient and long term strength ofsoft clay. Finally studied the shear creep characteristic of Shanghai soft clay via numericalsimulation based on the PFC2Din perspective from the bond water. All the studies abovereached conclusions as follows:The three kind of soft clay possesses the defining characteristic of soft soil. The particle size of Tianjin soft clay is the smallest, which can attract more bond water on its surface, so thenatural moisture content, plastic limit, liquid limit and plasticity index of Tianjin soft clay is thehighest among the three kind of soft clay, consequently, the physical-mechanical property ofthat is the poorest. Physical-mechanical property of Suzhou soft clay, by contrast, is the best.Physical-mechanical property of Shanghai soft clay is fall in between.With the highest secondary mineral content, smallest particle size and the most fine pore,Tianjin soft clay attracted the most bond water which is not easy to dissipate during the creepprocess, the Tianjin soft clay got a greater influence from the bond water, showed a moreobvious nonlinear creep characteristic. So the Tianjin soft clay possesses a higher secondaryconsolidation coefficient and a lower viscisoty coefficient. As a result of the more bond waterstucked in the fine pore, the decrease amplitude of long term strength of Tianjin soft clay islarger than Shanghai soft clay and Suzhou soft clay.The original microstructure of the three kind of soft clay includes skeleton structure,flocculated structure, honeycomb structure and lamination structure. After the creep test themicrostructure of soft clay changed into reunion structure, flocculated structure and clotstructure. Due to the decrease of macropore and the increase of fine pore, the microstructure ofthe three kind of soft clay became denser. The creep test changed the size distribution of theparticle and the pore, also changed the shape of them, their shape became more oblate, and thecomplicated degree of that decreased, furthermore the change of particle shape was moreobvious than the pore. After the creep test, particle directionality of the three kind of soft clayincreased in horizontal section, but decreased in vertical section. Moreover, the particledirectionality was higher after the consolidation creep test. The change of pore directionalitywas similar to parcitle, but it was independent of test method.Particle can attract more bond water with a small particle size and a big specific surfacearea, the specific surface area of Tianjin soft clay can be335.89m2/g, so the bond water contentin Tianjin soft clay was the highest. Although the bond water content was different from eachother among the three kind of soft clay, there was a obvious inflection point on their adsorptioncurve, p/ps=0.9, which was the boundary between firmly bond water and loosely bond water. The particle density after hydration, density of the bond water, film thickness of the bond waterand some other parameters were all obviously changed at this point.According to the result of creep test on remolded soft clay, there exist a relation of curvebetween the secondary consolidation coefficient, viscisoty coefficient, long term strength andthe bond water content. The three paramaters slightly changed during the firmly bond waterstage, as the bond water content close or exceed the firmly bond water content, the secondaryconsolidation coefficient sharply incressed as the bond water content, while the viscisotycoefficient and the long term strength decreased. The result here confirmed that soft clay withhigh moisture content was more likely happen to creep, while the loosely bond water was themain factor influencing the deformation and strength characteristic of soft clay during the creepprocess.The PFC2Dnumerical simulation result showed the strength index of the particles decreasewith the bond water content. The particle volecity silightly increased during the firmly bondwater stage, when come into the loosely bond water stage it increased obviously with the watercontent, as while higher bond water content resulted in a higher creep volecity in the steadycreep stage. The strain energy was nearly alike during firmly bond water stage, while it wasdecreasing sharply with the bond water when come into the loosely bond water stage. |
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