Implementation of the strain hardening model into buffer material in high level waste repository

Engineered Barrier System (EBS) primarily provides a protective cover for the High Level Waste (HLW) canisters. In addition, it functions as an efficient hydraulic and chemical barrier system. For in situ disposal applications, the ideal buffer material is bentonite and it is fabricated into blocks to build EBS. Currently, traditional methods introduce significant errors in constitutive modeling of those modeled blocks. In this paper, the particular failure laws and stress-strain laws of bentonite blocks were furnished from a lot of uniaxial and triaxial tests. Also, it showed that the stress-strain relations given by the traditional constitutive relations did not correspond to the failure forms of bentonite specimens in the experiments. On this basis, the relations between internal friction angle, cohesion and plastic strain were analyzed so that a new strain hardening model was established under the framework of Mohr-Coulomb criterion. In the end, a series of 3D computation of HLW disposal were carried out using the software FLAC3D, where the proposed strain hardening model led to satisfactory prediction of the buffer materials.