A Research Of Boom Clay Elastic-plastic Constitutive Model Considering The Coupling Effectsof Stress And Seepage

Mudstone is a clay rich mineral with low permeability,good creep characteristics,high adsorption and self-healing properties,but Boom Clay also has good expansibility besides above characteristics of mudstone which makes the good chemical closure of the Boom Clay formation.Belgium,France,Switzerland,Germany and other European countries agreed to decide the boom clay to be one of the best dispose formation of nuclear waste because of its good properties.Several countries in Europe have carried out underground experimental projects to systematically study more about the physical and mechanical properties of different mudstone formation.In this paper,the elasto-plastic mechanical properties and stress-seepage coupling characteristics of Boom Clay were studied by combining the HADES underground laboratory project in Belgium.The main contents are as follows:(1)The basic physical parameters such as stratigraphic distribution and particle size distribution of Boom Clay were analyzed.The results show that the stratigraphic distribution of Boom Clay is relatively uniform,and the particle size is mainly less than 32?m and less than 62?m.boom Clay's clay minerals composition accounts for about 60%,including illite,montmorillonite and kaolinite;non-clay minerals are mainly composed of quartz and feldspar.(2)The triaxial test data of Boom Clay were analyzed,and it was found that Boom Clay has obvious pre-peak hardening and post-peak softening mechanical properties.The internal variable was established by using the strain change in the whole stress-strain process in this paper,an elasto-plastic coupling model considering strain hardening and softening was proposed,and the finite element software ABAQUS was used to verify the model.It shows that the results calculated by this model can be used to reflect the deformation characteristics of Boom Clay in the actual triaxial compression process.(3)The evolution of permeability of Boom Clay in the process of compression deformation was systematically analyzed.By referring to the evolution of permeability of other types of rock in the whole stress-strain process,combining the internal variables established in this paper,the permeability evolution of Boom Clay was divided into three stages: the pre-expansion decrease stage,the post-expansion rapid increase stage,and the stabilization phase after the residual phase.In order to fully consider the influence of theexpansion point on the permeability mutation,the percolation theory was introduced.Based on the percolation theory,the Boom Clay permeability evolution equation considering the relationship between the confining pressure and the initial permeability and the peak permeability was established.(4)The Boom Clay stress-percolation coupling model was established by combining the Boom Clay elastic-plastic coupling model and the Boom Clay permeability evolution equation considered the confining pressure.The model was embedded into ABAQUS by USDFLD interface.The triaxial compression test of Boom Clay is simulated using the model,and the permeability evolution characteristics of the model were verified by the analysis results.(5)Based on the physical and mechanical parameters of Boom Clay and the Boom Clay model of stress-seepage coupling characteristics,the finite element model of shield tunneling in Boom Clay formation was established combining the CONNECTING GALLERY project of HADES underground laboratory in Belgium.The analysis of the stress,deformation and seepage characteristics of the surrounding rock during the excavation of the CONNECTING GALLERY project was carried out,which provides the basis for the analysis of the stability of the surrounding rock in the excavation of tunnel in the Boom Clay formation.