1999 Volume 52 Issue 3 Pages 3-10
A new simple shear apparatus was developed to evaluate the effect of soil suction on soil strength during shear deformation. The new apparatus clearly depicts shear deformation. It is thus most suitable for evaluating the effect of shear reinforcement by tree roots because it can preserve the fixed shear zone for the duration of the shear test. The new apparatus consists of the shear box (acrylic resin, 20cm×20cm×15cm) and the soil suction control section (poly-vinyl chloride pipe; 19.8cm in diameter, 50cm long). Using Toyoura standard sand, we evaluated the shear strength obtained by the new apparatus then estimated the effects of soil suction as related to soil strength and it's parameters (apparent cohesion and internal friction angle).
The results show that soil suction affects the soil strength, which depends on shear strain. The internal friction angle does not change under various soil suction conditions, but the apparent cohesion, which reached a peak in suction of-45 cmH2O near the critical capillary head, was effected by soil suction. The effect of soil suction on apparent cohesion abruptly changed in the range of 1 to 5% shear strain. These results demonstrate that the effect of soil suction on soil strength and apparent cohesion depends not only on shear failure but also on the process of shear deformation, which is significant in the range of 1 to 5% shear strain.
