This chapter describes the experiments undertaken on the Cambridge Geotechnical Centrifuge which modelled the free-fall penetrator option for subseabed high-level waste disposal. In these experiments, the impact and embedment of the penetrator on the seabed was modelled by firing a right cylindrical projectile at a sample of normally consolidated kaolin. A variation m penetration depth versus impact velocity was recorded This variation was compared with theoretical calculations based upon a semi-empirical relationship Measurements were taken of the changes in pore pressure as the projectile approached and passed a given point in the clay, and of the subsequent pore pressure decays After the penetration event, a consolidation period was allowed, accompanied. In two of the experiments by heat emission from the projectile Subsequent to this heating/consolidation stage, the centrifuge was stopped and a site investigation undertaken The disturbance of the soil and the degree of closure along the entry pathway was ascertained from this site investigation.
This chapter outlines the set of experiments undertaken at 100 gravities on the Cambridge beam centrifuge, in which the free-fall penetrator option for the disposal of high-level waste was investigated. In this option, high-level nuclear waste would be vitrified and placed in streamlined drop penetrators These penetrators would be carried to specified offshore sites and released into the water Self-weight would accelerate each penetrator up to a terminal velocity of 50–80 m s−1 (depending on the particular penetrator design), after which point the penetrator would impact upon the seabed and bury itself within the seabed clays The undetermined factors in the free-fall penetrator option are the likely depth of penetration for a even soil, the degree of closure of the pathway left behind the penetrator and the effects of subsequent heat emission (due to radioactive decay) upon the surrounding soils.
The present experimental programme was intended to complete a multi-year project at Cambridge in which various aspects of this waste disposal option were investigated, and included reports by Parker (1982), Savvidou (1984) and Poorooshasb (1984) In particular, the present experimental work, reported in greater detail in Poorooshasb (1987), was designed to combine the dynamic penetration aspects reported by Poorooshasb (1984) with the heat transfer phenomena reported in Savvidou (1984) The boundary conditions associated with the present experiments were considered to be the most realistic of the Cambridge work, and so the results were also expected to be the most appropriate
The scaling laws relevant to this problem can be summarized as follows (Savvidou, 1984), where a quantity which models at a scale factor of n is larger in the model than in the prototype (The Formula is available in full paper) Assuming that effective stresses rather than the total stresses were important in the problem, it was possible to design an experiment using these scale factors which would model the prototype event.