Effect of suction on shear strength of soils

本研究探讨了吸力对非饱和土抗剪强度的影响，采用冈山生产的非饱和Masa土进行了试验。将试件静压在三叶教授研制的直剪仪剪切箱中。通过埋入装置下压板的陶瓷圆盘对试件进行吸力，在恒定吸力条件下进行应力控制引流剪切试验。正应力设置为1.0、2.0、3.0kgf/cm2，吸力设置为0、0.1、0.2、0.4、0.6、0.8kgf/cm2。试验结果表明，抗剪强度随吸力的增大而增大。然而，在0.4kgf/cm2的吸力范围内，剪切强度的增加可以忽略不计。正常压缩和超压马萨土表现出相同的抗剪强度随吸力增加的趋势，两球间的孔隙水产生的粘结力导致有效正应力的增加，进而导致抗剪强度的增加。从理论上计算了相同尺寸球体随机堆积条件下的作用力。吸力与抗剪强度的理论关系与实验结果吻合较好。

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.