高掺砂率膨润土混合土膨胀特性及其膨胀量预测

膨润土与砂混合土中掺砂率的高低会引起混合土膨胀特性的差异。对纯膨润土及其低掺砂率混合土,浸水膨胀完成后蒙脱石孔隙比em与竖向应力σv在双对数坐标内呈唯一线性关系。对高掺砂率混合土,在较小荷载下浸水,不会形成砂骨架,em–σv线性关系仍成立;在较大荷载下浸水,会形成砂骨架,砂骨架形成后,em与σv间不再满足该线性关系。利用砂骨架孔隙比的概念可确定不同掺砂率混合土形成砂骨架时对应的起偏应力及混合土能够形成砂骨架的临界掺砂率。砂骨架形成前,砂颗粒被蒙脱石包围,外力由蒙脱石承担,最终变形量由试样中单位体积蒙脱石的含量决定。砂骨架形成后,竖向应力最终由砂骨架和蒙脱石共同承担,提出了确定不同掺砂率下两者承担比例的方法,进而可确定砂骨架形成后的膨胀变化量,预测结果与膨胀试验结果吻合较好。该方法可以预测高掺砂率混合土的浸水膨胀量。

Swelling characteristics of bentonite-sand mixtures with a high sand mixing ratio and its prediction

The mixing ratio of sand influences the swelling characteristics of bentonite-sand mixtures. As for the pure bentonite and bentonite-sand mixtures with low sand mixing ratio, the relation between montmorillonite void ratio e_m and vertical stress σ_v is a unique line in their logarithmic coordinates. However, for the mixtures with high sand mixing ratio, sand skeleton will not be formed when the specimen is wetted under a small vertical stress, and the linear relation between e_m and σ_v is still satisfied. When the stress is larger than ‘deviation starting stress’, the sand skeleton is formed and e_m value deviates from the line. According to the concept of sand skeleton void ratio, the ‘deviation starting stress’ when the sand skeleton is formed can be determined for the mixtures with different sand mixing ratios, and the range of sand mixing ratio in which the sand skeleton may be formed can also be obtained. Before sand skeleton comes into being, sand particles are surrounded by montmorillonite, hence the vertical stress is mainly burdened by montmorillonite, and the swelling quantity at full saturation including swelling deformation and swelling pressure is determined by the montmorillonite content per unit volume. After the sand skeleton is formed, the vertical stress is burdened by the montmorillonite and sand skeleton. A method is proposed to determine the load sharing ratio burdened by the two parts, and subsequently, the swelling can be obtained after the sand skeleton is formed. The proposed method is testified by the swelling test results, and it can predict the swelling variations due to wetting for the mixtures with high sand mixing ratios.