Study On Expansive Soil In Drying-Watering Cycle And Constitutive Models Considering Overconsolidation And Structure

The expansion soils have negative effect on various constructions, including road foundation uneven sinkage, bulge and cracking, slope slippage, collapse and hill-creep, house cracking as well, in alternation of wetting and drying situation. Therefore, the studies on compressibility of expansive soil in drying-wetting cycle process and on constitutive models which describes special behavior of it have theoretical and practical significance. In this paper, Nanning expansive soil’s intact, reconsolidated and drying-wetting cycle samples in one-dimensional compressions are studied, and constitutive models which reflects the impacts of overconsolidation and structre also. Subsequently, the model’s application is achieved by means of subroutines related to finite element softwar, i.e. the numerical simulation platform is established. Later, the rationalities of models and subroutines are verified in a series of numerical simulations. Finally, Boom Clay and Fujinomori Clay are simulated, the results are compared with the test data and the results of other models.The studies on experimentations indicate that, the drying-wetting cycle generates sub-structure proposed in this paper which has contrary influence on expansive soil compared with structure. Before consolidation pressure is less-than sub-structure yield stress, drying-wetting cycle has nothing to do with compressibility of expensive soil. When consolidation pressure is greater-than sub-structure yield stress, the sub-structure begins to decay, consequencly, the stiffness of expansive soil diminishes. At last, if the sub-structure is thoroughly damaged, the stiffness of expansive soil is immune from drying-wetting cycle and equivalent with reconsolidated soil.In respect of studies on constitutive models, the subloading surface model with improved overconsolidation state variable is established for describing the influences of overconsolidation in expansive soil. The model can precisely simulate varieties of pore ratio and effective stress, deformation and stress-strain relationships of overconsolidation soil in compression process, furthermore, it can imitate stress-strain curve of overconsolidated soil slickly. Besides, the model’s simulations for Fujinomori clay in superior overconsolidated state can more approach the actual characteristics such as strain softening, peak and residual strength than unified hardening model.To disicribe the influences of overconsolidation and structual characteristics on expansive soil, the super-subloading surface model with improved state variable is put forward. The model’s simulations are equivalent to common disciplines of overconsolidated soil and struactured soil, for instance, soil stress path, variation of pore water pressure, stress-strain relationships and so on. And the model can imitate peak and residual strength, nolinear relationships, and strain softening for intact Boom clay and Fujinomori clay. Moreover, the model can portray the influences of principal stress axes rotation more suitably compared with the model of Nakai and Hinokio.The subroutine library of finite element softwar has been extended in this paper by establishing the constitutive models considered overconsolidation and constitutive property, accordingly, the applications of the models proposed in practical project have been founded, thereupon, the practical application of these models can be expected soon in pace with further qualitative investigations and quantitative studies on expansive soil’s overconsolidation and structure.