Abstract: Loess is a typical unconsolidated soil with structural strength. Its special structure results in an obvious turning point (where the pressure is called the compressive yield stress of structure) on its compression curve, similar to the curve of over-consolidated soil. To analyze the effect of initial structure on compressive yield of loess, confined compression tests and uniaxial compression strength tests were conducted on loess soils from six sites. The compressive yield stress and the structure index of loess with different water contents were obtained respectively. The results show that the structure index and the compressive yield stress of loess decrease with the increasing of water content. Meanwhile, with the increasing of water content, the variation of structure and variation of compressive yield stress are small. With the same sedimentary period of loess , greater structure index results in greater compressive yield stress. However, the linear relationship between structure index and compressive yield stress is different for the loess in the different sedimentary periods. The expressions of such correlations for Q3 (late pleistocene) loess and Q2 (middle pleistocene) loess are given respectively. Furthermore, the applicability of the correlations is verified by examples. Taking the structure as a bridge, there is a way to calculate compressive yield stress by using simple and easily available physical indexes.

Key words: soil mechanics, undisturbed loess, initial structure, structure index, compressive yield