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.