A series of tests has been undertaken on a variety of different soils to understand how soil cuttings disaggregate when pumped from the tunnel face to the separation plant during slurry tunnelling for pipe jacked tunnels. It is important to understand this process to ensure that the separation plant can be optimised to remove the maximum amount of soil from the slurry prior to the reuse of the liquid. In pipe-jacking operations this liquid is normally water, which is recirculated after the soil has been re-moved to minimise and if possible eliminate the production of liquid waste. The paper will present results from a series of “mixing tests”, devised by the authors to investigate disaggregation, and also from standard laboratory tests undertaken to establish basic soil properties such as soil strength. The “mixing tests” simulate the softening of the cuttings due to the presence of water and the shear forces applied to the slurry by the pumps and have al-ready allowed the effect of these factors to be quantified. This series of tests will demonstrate how the mechanism of disaggregation varies with strength resulting in different proportions of disaggregated soil particles in slurries subjected to the same mixing time and shear forces
