556 ENGINEERING GEOLOGY/Problematic Soils Figure (A) Liquefaction of sand due to the Tangshan earthquake (28 July 1976) near Dougtian, China (B) Collapse of buildings because of liquefaction of fine sands and silts, Niigata, Japan, 1964 residual soil tend to develop a metastable fabric as fine particles are removed As a consequence, the weathered products are potentially collapsible Truly collapsible soils are those in which collapse occurs on saturation since the soil fabric cannot support the weight of the overburden When the saturation collapse pressure exceeds the overburden pressure, soils are capable of supporting a certain level of stress on saturation and can be regarded as conditionally collapsible soils The maximum load that such soils can support is the difference between the saturation collapse and overburden pressures These soils generally consist of 50 to 90% silt particles, and sandy, silty, and clayey types have been recognized, with most falling into the silty category (Figure 2) The fabric of collapsible soils generally takes the form of a loose skeleton of Figure Particle size distribution of loess