Two versions of the system are available, a dynamic and a lower cost "static" version. GDS HCA has been built specifically for very accurate long-term work with the capability for a level of dynamic performance. There has been excellent work carried out using GDS systems at LNEC, Portugal, University of Southampton, UK, amongst others. In addition there is a paper in Ground Engineering where the researchers have chosen to use the GDS approach along with a number of GDS components. For the full specification of the Hollow Cylinder apparatus click here.