A new method for evaluating loess collapsibility and its application

Collapsibility affects loess engineering stability. Currently, there are two methods used to determine the collapsibility of loess: the traditional indoor collapsibility test (indoor test) method and the field immersion test (field test) method. However, for the same loess site, the collapse values under overburden pressure obtained by the two methods are quite different. For sites that cannot be tested in situ, it is easy to misjudge the collapsibility of the loess foundation when depending only on indoor test results. To improve the accuracy of the indoor collapsibility determination, the characteristics of the compression curves obtained from confined compression tests at six different loess sites are analyzed in this paper. The compression curves of loess under different states are normalized and described by the composite power exponential model. The collapsibility of loess is closely related to its structure. A new method for analyzing and evaluating the collapsibility of loess is proposed; the method combines the relationship between the compression characteristics and initial structural properties of loess and the relationship between the initial structural properties and physical comprehensive indexes. To verify the applicability and accuracy of the new method, the collapse values under overburden pressure of two test sites along the Xi'an Metro Line 5 were calculated using the physical indexes of loess at different depths and compared with the values calculated from the indoor test and field-measured values. The results show that the calculated value of the new method is closer to the measured value of the field test than is the calculated value of the indoor test, and the new method can correctly determine the collapsibility type and grade of the site. The new method provides a simple and feasible means by which to correctly and quickly evaluate site collapsibility in loess engineering, which is beneficial for conducting loess site collapsibility evaluations under full operation to develop and implement the measures of foundation treatment in loess areas. The method can be used as a reference at loess sites where field tests cannot be performed.