The sandy loess in the desert-loess Plateau transition zone exhibits obvious collapse deformation when it encounters water. The collapsibility of the sandy loess in Changqing Oilfield

widely distributed in Jingbian

northern Shaanxi province

is seriously influenced by the collapsibility of sandy loess. It is urgent to reveal the collapsibility characteristics and mechanism of the sandy loess in Changqing Oilfield construction. Therefore

taking the sandy loess of Jingbian Q in the transition area of Jingbian Desert-Loess Plateau in northern Shaanxi as the research object

the basic physical properties and material composition of the sandy loess were analyzed using laboratory basic physical properties

X-ray diffraction and collapsibility tests. The collapsibility characteristics

influencing factors and rules were clarified. On this basis

the microstructure

pore size distribution

directional frequency and abundance changes before and after the collapse of sandy loess were explored using scanning electron microscopy test and pore and fissure image recognition analysis. The collapse mechanism of the sandy loess was revealed from a microscopic perspective. The results show that the Jingbian Q sandy loess has collapsibility. The collapsibility coefficient first increases and then decreases with the increase of axial pressure

and it gradually decreases with the increase of dry density and moisture content. The collapsibility coefficient peaks at the axial pressure of 150 kPa. Jingbian Q sandy loess is mainly composed of quartz

albitite

muscovite and calcite. The grain morphology is mostly angular or subangular

with overhead arrangement structure and overhead pores

and point-to-point contact. Clay cements are mostly distributed in the contact areas of skeleton particles. The collapse of the overhead pore structure in Jingbian Q sandy loess is the essence of its collapsible deformation

providing the main space for collapse. Subsidence deformation

caused by the coagulated structure formed by a small amount of debris particles wrapped in the clay cement

contributes to the increment of collapsible deformation. The research results provide a data basis for evaluating the collapsibility of sandy loess in the construction area of Changqing oil and gas field engineering.