Effect of suction on shear strength of soils

本研究以冈山生产的MASA非饱和土为试验材料，探讨了吸力对非饱和土抗剪强度的影响。试件在米卡萨教授开发的直剪仪的剪切盒中静态压实。通过装置下压板中的陶瓷圆盘对试样施加吸力，在恒定吸力条件下进行应力控制排水剪切试验。试验结果表明，随着吸力的增大，剪切强度增大，剪切强度随吸力的增大而增大。然而，在吸力为0.4 kgf/cm ^2的范围内，剪切强度的增加可以忽略不计。正常压缩和超压缩MASA土的抗剪强度随吸力的增加呈现相同的趋势，孔隙水在两球体间产生的粘结力使有效正应力增加，从而使抗剪强度增加。在相同尺寸的球体随机堆积的条件下，对力进行了理论计算。吸力与抗剪强度的理论关系与试验结果吻合较好。

This research report discusses the effect of suction on the shear strength of unsaturated soils.Unsaturated MASA soil produced in Okayama was used in experiments. The test specimens were statically compacted in the shear box of direct shear apparatus developed by Prof. MIKASA. Suction was applied to the specimens through the ceramic disc imbeded in the lower pressure plate of the apparatus.Stress-controlled drainage shear test were carried out under the condition of constant suction. Normal stress was set to 1.0, 2.0, 3.0kgf/cm^2 and suction to 0, 0.1, 0.2, 0.4, 0.6, 0.8 kgf/cm^2.The test result shows the increase of shear strength with the increase of suction. However, the increase of the shear strength is found to be negligible over the range of 0.4 kgf/cm^2 of suction. The normally compressed and over-compressed MASA soils show the same tendency of the increase of the shear strength with suction.The bonding force produced by the pore water between two spheres causes the increase of the effective normal stress, then the increase of the shear strength. The force is calculated theoretically under the condition of random packing of the same size spheres. The theoretical relationship between suction and shear strength shows the good agreement with the experimental results.