A triple‐microstructure hydro‐mechanical constitutive damage model for compacted MX80 bentonite pellet/powder mixture

Abstract

AbstractA triple‐microstructure hydro‐mechanical constitutive damage model was proposed to describe the hydro‐mechanical behaviour of MX80 bentonite pellet/powder mixture, based on the results from a series of suction‐controlled oedometer tests and microstructure observations. Emphasis was put on the pellet damage behaviour. The model parameters were determined essentially based on these results. The model response was firstly verified with the obtained oedometer tests. Then, the results of Molinero‐Guerra et al. and Darde who carried out suction‐controlled oedometer tests and swelling pressure tests on similar bentonite pellet/powder mixture were employed to validate the proposed model. It appeared that the global volume behaviour and the development of swelling pressure with suction of the bentonite mixture could be well reproduced. The model allowed gaining insights into the microstructural evolutions under oedometer loading. The global compression behaviour was governed by the filling of inter‐grain pores at unsaturated state, but by the compression of grains themselves at saturated state. Conversely, when wetted under constant‐volume condition, inter‐grain pores and intra‐grain macro‐pores were closed, by the swelling of intra‐grain micro‐pores. Examination of the water‐retention property showed that water saturated the intra‐grain micro‐pores at suction 19 MPa, and then started filling intra‐grain macro‐pores. When inter‐grain pores and intra‐grain macro‐pores were all closed at suction 0.1 MPa, water finally came back to intra‐grain micro‐pores. On the whole, the hydro‐mechanical behaviour of the bentonite pellet/powder mixture can be well described by the proposed model.