The natural diatomaceous soil widely-deposited in Ohita Prefecture of Japan is a surprising natural sedimentary soil with a normally-consolidated history. Its water content is very high

but its stiffness is so high that it can keep its intact state without suffering from the effects of sample disturbance during sampling and handling. The high quality and strong resistance of soil structure provide a unique chance to investigate the mechanical behavior with intact samples in laboratory. A high-pressure triaxial apparatus is used to perform isotropic consolidation tests and triaxial consolidated undrained shear tests. The results indicate that the compression curve of structured soils is a horizontal line from the initial void ratio in preyield state

and the compressibility changes dramatically in the vicinity of the consolidation yield stress. The strength behavior shows that the strength of structured soils is independent of stress level in preyield state

but the strength envelop in postyield state is a straight line through origin which is similar to that of remolded soils.