For the construction of two tunnels in the western area of the Koralm rail track the stability of soil mainly constituted by lacrustine clay sediments has to be artificially improved. In the high pressure jetting method the compressive strength of soil is increased by injection of cement suspension. In response large amounts of suspension emanate from the boreholes, which have to be prepared for further use or disposed. To develop an appropriate processing system for the cement containing slimes, the dewatering properties had to be elaborated with regard to the solids particle size distribution and mineral composition, electrochemical properties and varying volume concentration of solids and cement. Laboratory settling tests using 1 l cylinders under variation of size distribution, solid´s and cement concentration revealed a property matrix to describe the sedimentation behaviour and the consolidation of the sediment. Pressure filter tests with successive shear box tests of the filter cake gave insight into the filtration resistance, cohesion and inner friction of the dewatered soil. On the base of these data the need and the design of a dewatering system composed of appropriate apparatus for handling cement containing slimes is discussed.