Hydro-mechanical Coupled Creep Damage Constitutive Model Of Boom Clay, Back Analysis Of Model Parameters And Its Engineering Application

Clay stone is a common soft rock in the construction of underground engineering, which has siginificantly rheological characteristics. The failure mechanism and long-term stability of underground engineering in clay formations under thermo-hydro-mechanical coupled situation have become a hot issue in rock mechanics and rock engineering. It is commonly considered that clay is a good potential permanent storage medium for geological disposal of high level nuclear wastes because of its low permeability, creep and self-healing. France, Belgium and Switzerland have constructed undeground laboratory in clay to investigate hydro-mechanical coupled and long-term creep behaviour of clay.Combining with site investigation in Belgium, the main research has been conducted on hydro-mechanical coupled, permeability and creep damage behavior of Boom Clay. The main achievements are as follows:(1) A modified Mohr-Coulomb criterison is established considering low tensile strength of Boom Clay. Based on the implicit Euler integration algorithm, UMAT subroutine of the modified Mohr-Coulomb model is programmed in business code ABAQUS. Based on the defined damage potential, an elasto-plastic damage model with Mohr-Couloumb criterion is established to describe hardening and softening behaviours of Boom clay. Furthermore,damage evolution equation is suggested and programmed in UMAT.(2) Based on the latin hypercube sampling method, a new evaluating sensitivity of system parameters is put forward by Spearman coefficient in non-parameter statistics. The lateral Geostress coefficient method for 3-D in-situ stress inversion is introduced. A methodology of inversion analysis combining the Nelder-Mead algorithm and finite element method together with ABAQUS is proposed. Then, a new exact penalty function is constructed between the monitored data and numerical results. The algorithm is programmed in Matlab.(3) Based on the developed numerical code in ABAQUS, parameters for Boom clay elasto-plastic damage model are obtained according to undrained triaxial consolidation tests by back analysis.(4) A fully coupled hydro-mechanical model of Boom clay is established to describe the evolution of porosity and permeability with stress and strain. Based on the permeability experiment results in Lab and site, a hydro-mechanicalcoupled damage model is developed. A permeability healing model is established by introducing the conceptions of healing stress and hydro-chemical factor. Based on field monitoring data of pore pressure, the permeability and parameters of the hydro-mechanical coupled damage model and permeability healing model are obtained by back analysis.(5) Based on laboratory creep test results of Boom clay, a nonlinear creep constitutive model considering hydro-mechanical coupling is put forward by construction the equation between creep damage and creep strain, which is programmed in UMAT by the method of the explicit integration scheme with the Mohr-Coulomb creep potential. The creep parameters of Boom clay are acquired by the method of displacement back analysis and in-situ monitoring results of deformation for about 20 years.(6) Based on the achievements stated above, the long-term stability of test drift and connecting gallery in Belgium is predicted. The evolution law of pore water pressure, excavation disturbed zones, and permeability with time is obtained.