A water conveyance open channel project in the northern Xinjiang region crosses a large area of collapsible loess. The mechanical properties of the collapsible loess have undergone severe degradation after years of exposure to rainfall

evaporation

and seasonal temperature fluctuations

making it highly susceptible to engineering phenomena such as channel foundation collapse and slope failure. To delve into the deterioration mechanism

direct shear

compression

and microscopic scanning tests were conducted on the collapsible loess under dry-wet & freeze-thaw cycles. The deterioration patterns of shear strength and compression properties

as well as their damage mechanisms

were analyzed at both macro and microscopic scales. The results of the study indicate (1) Straight shear test: with increasing the number of dry-wet-freeze-thaw cycles

the peak shear strength exhibits a three-stage trend: rapid decrease

decelerated rate of decrease

and eventual stabilization. The cohesion decreased exponentially

with the largest reduction occurring during the first cycle

and stabilizing after 5 cycles

reaching a degradation degree of 44.55%. The change in internal friction angle

which varied within 2.1°

was less affected by the wet-dry-freeze-thaw cycles

with a maximum degradation of 7.04%. (2) Compression test: the compression curve can be divided into two stages of elastic deformation and elastic-plastic deformation according to the consolidation yield stress k

and k shifts forward as the cycle times increase. The compression coefficient and compression index decreased exponentially or in a power function form with increasing cycle times

indicating reduced overall compressibility of the soil body. (3) Microstructure: through scanning electron microscope (SEM) analysis

under cycling

the number of large pores decreased while the number of medium and small pores increased

with the arrangement tending towards disorder. Large particles gradually transformed into medium and small particles

and their morphology tended to become rounded. Correlation analysis indicates that pore size and its angle are the main factors influencing shear strength. Pearson’s correlation coefficient reveals that particle morphology and pore size have the greatest influence on compression indices.