ベントナイトゲルのすべり破壊

抄録

Gotoh and Hirai¹⁾ found that the blocks of bentonite hydro-gels showed clear slip bands under critical pressure and the bands inclined at 45°in the direction of the force given. The slip patterns could not be observed with the specimens treated at above 800°C or with those dispersed in organic liquids. Gotoh, Hanai and Aida²⁾ investigated the viscoelastic behavior of the bentonite gels with the cone and plate viscometer and found that the gel slipped at certain critical shear stress.
In this report, the critical shear stress at which the slip bands appear was measured at various concentrations of Wyoming bentonite dispersed in water. The critical shear stress was observed with the following three kinds of method; (1) a compression method (Fig. 1), (2) a cone and plate viscometer method and (3) a two surface shearing box method. Fig. 2 shows a typical slip band observed by the compression method. Fig. 3 shows the viscoelastic behavior and slip of the bentonite gel observed at various shearing loads. Fig. 4 shows the relation between the critical stress and the concentrations. The results obtained by the three kinds of method fall on the same line which shows a characteristic curve analogous to the relation between the elasticity of gels of high polymers and their concentrations³⁾. It has been shown that the instantaneous elasticity of the bentonite gels shows also the same tendency with respect to their concentrations.
These results suggest that the bentonite gels has a network structure analogous to that of high polymers, but that the binding force is very weak in comparison with that of polymers. Further, it has been observed that a polarized light can pass through a thin film of the bentonite gel placed between two parallel glass plates at the instant when the plates are sheared (Fig. 6). This result suggests that the bentonite particles can be oriented under shearing stress, and such orientation may make the bentonite gels easy to slip.