A comprehensive study was carried out on the influence of Hydroxypropylmethylcellulose (Methocel F50 - HPMC) on the mechanical properties of a reference sand. It was found that the nonlinear dependence of viscosity on HPMC content is in agreement with literature data. As far as the mechanical properties are concerned, no additional cohesion is generated. There is also no significant effect on the friction angle determined in the shear box and triaxial tests. The effective permeability of sand specimens can be significantly affected by changing the viscosity and thus reduced accordingly. The mechanical influence on the overall stress-strain relationship (strength as well as stiffness parameters) in the triaxial device is marginal when the pore fluid is replaced with an HPMC solution.
Offshore foundations are particularly exposed to cyclic loads. Cyclic loads generally lead to the accumulation of soil deformations and thus to changes in the stress conditions in the soil - which in turn induces a change in the load-bearing behaviour of the foundation. The loads also lead to an accumulation of excess pore water pressures with a corresponding reduction in strength and load-bearing capacity. Accordingly, the design of foundations must focus strongly on the effects of cyclic loads. For an investigation of partially drained conditions, which may arise during a storm event, 1g-small-scale tests can be carried out. The main problem with 1g-model tests is that for realistic drainage conditions, smaller permeabilities are needed compared to the available grain size for cohesionless soils. Problems in measuring excess pore water pressure build-up and cyclic accumulation result from the relatively short drainage paths and the still comparatively high permeability of the fine sand. A remedy can be the use of biodegradable and non-corrosive water thickeners. These increase the viscosity of the water in a controlled manner and produce a lower permeability of the sand body with the same mechanical properties.
