LABORATORY STUDY ON COLLAPSIBILITY OF TYPICAL LOESS UNDER UNSATURATED HUMIDIFIED CONDITIONS

We utilized a self-made device to humidify an undisturbed and typical loess sample(column) to different degrees of saturation. During the humidification process,we analyzed the distribution of water at different locations in the soil sample. We conducted the collapsible test on samples after the humidification process. We defined the unsaturated humidified collapsible coefficient to discuss the different positions and total collapsibility of the sample under unsaturated humidified conditions. As the target water content of low-humidification samples increases over time,the water content of the upper layer decreases gradually,while the water content of the lower layer increases. The distribution of the water content in the loess column is uneven. In contrast,as the target water content of high-humidification samples increases over time,the water content of the upper layer decreases at an increasing rate,while the water content of the lower layer increases at an increasing rate. Furthermore,the distribution of the water content in the loess soil column is even,and the time required to achieve an even distribution is reduced. As the target water content increases,the unsaturated humidified collapsible coefficient of each layer of the loess column increases at a faster rate; moreover,the coefficients of the bottom layer and upper layer tend to become more similar. The total unsaturated collapsible coefficient of the loess column increases with pressure at an increasing rate. When the target water content is low,the time needed for humidification is longer,which leads to shorter unsaturated humidified collapsible coefficients. In contrast,when the target water content is high,the time needed for humidification is reduced,which leads to larger unsaturated humidified collapsible coefficients. Our study on the collapsible characteristics of the loess column shows that the construction of a large-thickness loess site cannot be evaluated by the collapsible coefficient; instead,consideration of the water content,time,and pressure is required. Our results provide important insights into the evaluation of the unsaturated collapsibility of loess.