Abstract: Loess is a soil with a special structure. Currently the studies of influence factors on loess structure are mostly qualitative analysis using single factor. Structural index reflects the initial structure of loess. To study the influence of the physical parameters on the initial structure, firstly, unconfined compressive strength tests are conducted on the undisturbed and remolded loess samples with different water content taken from Xi’an and Lanzhou. Next, the corresponding structural indexes of loess are obtained. The analysis shows that the value of structural index decreases with the increasing of water content, dry density, minimum density ratio, plasticity index and liquidity index. In addition, it is also related with the geological period and geographical distribution of loess. Secondly, according to the above conclusions, a comprehensive physical index is constructed by the fundamental physical indexes. The relationship between the structure and the comprehensive physical index is further analyzed. The empirical formulas are obtained which can directly calculate structure index quantitatively by the comprehensive physical index considering the distinction between the geographical zonation and geological periods. Finally, by the comparisons of the structure indexes obtained by test for another loess field in Xi’an and the structure indexes calculated by the empirical formulas herein, their rationality and applicability are verified. These formulas provide a simple and easy method for quantitative calculation of the structural index by physical indexes to measure in the future.

Key words: loess, structure, physical index, quantitative calculation, empirical formula