Abstract: Since the layered soilbags is a congeries of individual soilbags, the discontinuous surface between the soilbags has the effect to reduce and absorb the vibration energy when it is used as foundation for low-rise building. However, the dynamic behaviour between soilbag interface was rarely studied so far. Using the large-scale direct shearing apparatus, the cyclic shearing tests were conducted on the soilbag interface and pure natural sand, and the variations of the shear stress, vertical displacement, dynamic shear stiffness, and equivalent damping ratio with shear displacement were compared. In addition, the interfacial frictional behaviour between the upper and lower soilbags was discussed. The results show that the initial shear stiffness, peak shear stress, and strain softening behaviour for soilbag interface are reduced compared to those of pure natural sand, but the shear stress-displacement loop is larger. The skeleton curve of soilbag interface can be better described using the Kondner-Zelasko model. For soilbag interface, an obvious contractive deformation is observed during cyclic shearing, while the dilatation is only observed under the low vertical stress and large shear displacement. The total contraction increases with increasing vertical stress, cyclic number and shear amplitude, and the change of vertical displacement within each cycle is smaller than that of pure natural sand. Additionally, the dynamic shear stiffness of soilbag interface is smaller than pure nature sand, but the equivalent damping ratio becomes larger, which indicates the advantage of soilbag structures to reduce vibration.

Key words: soilbag interface, dynamic behaviour, cyclic shearing test, damping ratio, vibration reduction material