Volume 21, Issue 1 (March 1998)
Influence of Viscous Fluids on Properties of Sand
The time scale for dynamic events differs from that for consolidation events if the same soil and pore fluid as in the prototype are used in a model test. In order to satisfy the scaling relationship for dynamic centrifuge tests, viscous fluids such as silicone oil or glycerin-water mixtures have been used as the pore fluid. The use of a pore fluid with higher viscosity will significantly reduce the permeability of a soil, making it possible to achieve the same time scale. However, the use of viscous fluids may also affect the mechanical properties of soils such as strength and stress-strain relationship. This paper presents results of permeability tests and triaxial tests on two types of sands over a range of void ratios. It is found that using a glycerin-water mixture as the pore fluid has little effect on the strength and stress-strain relationship of Ottawa sand No. 40. For tests with both silicon oil and glycerin-water mixture as permeants, coefficients of permeability are inversely proportional to the viscosity. However, at small hydraulic gradients, it was observed that the highly viscous fluids can cause clogging of flow in sand, especially for silicone oil in dense sand. It is recommended that when a viscous fluid is used in a centrifuge test, it is desirable to conduct a sequence of laboratory tests to make sure there is no unexpected influence on the properties of a soil.