Metropolitan Adelaide is founded on a wide variety of soils that overlie sediments and rocks. Some of the soils and sediments react to seasonal and human-induced changes in water content with marked changes in volume. The black earths and smectite-illite rich gley clays are the most reactive materials, and pose the greatest geomechanical problems. Two previous studies concentrated only on the upper 1 to 2 m of soil, but subsequent investigations indicate deeper clays are equally reactive and are responsible for many building cracks and footing failures. This study, jointly sponsored by MESA and CSIRO Division of Soils, has established a series of 170 cored holes (benchmark sites) drilled to 10 m depth where possible. Samples from the cores have undergone geomechanical and soil tests which include: Atterberg limits, particle size analysis, solute electrical conductivity, and a new swell-shrink test (SST). This new test has yielded: strains (vertical, horizontal, volume), water contents at fixed suctions (pF 3.0 and sorption limit pF 6.34) and wet bulk density. A series of derived parameters from the SST are also presented and include: water content and suction at the shrinkage limit, and an instability index (Ip t - based on total suction). A limited number of reactive soils and clays were examined using powder X-ray diffraction techniques to determine their mineralogy. More than 1500 m of core from this study have been retained for future reference at the MESA Core Library, Glenside. The results of the investigation are presented in tabular and graphical forms, with discussion and analysis provided within 8 Chapters and 4 Appendices. Direct observations and measurements from each cored hole are presented on multi-disciplinary Composite Log Sheets that display groundwater intersections plus textural, pedological, geological, and engineering descriptions as parallel logs, together with core sample test results. The derived values and indices are separately tabulated. Soil and geological units are individually described, then placed into context within the main geomorphic zones of the study area. Key geomechanical features are indicated for each unit and geomorphic zone. Testing has demonstrated that the majority of Adelaide's reactive soils are composed of clays with a high affinity for water (smectite, illite, randomly interstratified illite-smectite, and occasional vermiculite), and contain much less kaolin than less reactive soils. Black earth soils are only half as reactive as the substrate Keswick Clay. The instability index Ip t is a useful indicator for evaluating the potential reactivity of a site, and some rapid methods are presented for obtaining this value from conventional testing. However, Ip t values should be used cautiously where high clay solute concentrations are involved. A limited statistical analysis of the data is provided for each test parameter. Geomechanical problems are presented that are relevant to building footing design. These are associated with substrate defects, gilgai, trees, changes to site environment, and seismicity.