Research methods: Based on the understanding of the existing literature to the loess the reason and the mechanism， taking the loess classification sub-area project of motorway in loess regions of Gansu Province for example，the 9 physical mechanics index of the 59 groups are picked out in the routine soil test data. And the author uses factor analysis of multivariable statistical analysis methods to analyze loess physical mechanics index and has discussed the essential reason of loess collapsible.
Research conclusions: Between collapsible index of loess and other physical mechanics index of loess exist relevance， the foundation of loess collapsible is the space of loess，non-saturated loess and the joint of loess which meet the water intensity reduces，the main reason of loess collapsible is support hole existence. The loose and the porosity reflected the support hole existence. The clay content and the clay joint in collapsible the function need further to discuss. Simultane- ously，the result also indicates factor analysis to analyze loess is superior in solving the problem that it can not be shown for cross of index in general single factor analysis.
2007, Vol. 24 
