Experimental Study On Humidifying Deformation Of Loess

Collapsibility is a special engineering geological property of loess,which will cause foundation damage and engineering loss.In order to calculate the collapsibility of unsaturated loess more accurately,a simple model for predicting collapsible deformation of loess in Heping town of Lanzhou is put forward in this paper according to the theory of unsaturated infiltration and unsaturated deformation.Based on the large-scale on-site immersion test,the site gravity collapsibility was measured on the spot.After digging the exploration well and taking Q₃ loess samples of different depths,all the samples were analyzed by particle analysis,their conventional physical and mechanical indexes were measured,consolidation tests with different water cut were done,and their soil-water characteristic curves were measured.Through the analysis and study of the above experimental data,the following results have been obtained:（1）The site is the IV terrace of the Yellow River,and the loess is sandy loess.The thickness of the collapsible soil layer is 24 meters,and the site belongs to iii grade gravity collapsing.The collapsibility is mainly medium collapsibility and weak collapsibility,a few loess collapsibility is strong,the collapsibility coefficient decreases gradually with the increase of depth,and the sensitivity of collapsibility is general.（2）The actual collapsibility of the site is related to the depth of immersion.In the field test,it is necessary to determine the thickness of the collapsible soil layer and the corresponding immersion time in order to make the collapsible soil fully collapsible,so that the total amount of collapsible soil can be obtained.If the immersion time is limited,the wetting front depth should be measured and the actual collapsibility of the collapsible soil layer should be calculated in order to obtain a reasonable correction coefficient.（3）The compression test of controlling suction shows that the deformation of loess in this site goes through three stages in the process of decreasing suction and increasing humidity:pre-collapse phase,collapse phase and post-collapse phase.The pre-collapse phase occurs when the soil mass is in the high matrix suction,the matrix suction decreases,the soil mass deforms in small volume,and the soil structure remains intact.The collapse phase occurs within the intermediate suction range of the soil,with the decrease of matrix suction,the volume of soil becomes smaller,the intergranular connection of soil is weakened,and the structure of soil is destroyed.The post-collapse phase,the suction of the soil matrix is small,when the soil is close to saturation,with the decrease of the suction of the matrix,the volume of the soil varies little or no change.（4）A prediction method of loess collapsibility based on constant water content test results and characteristic curves of humidified soil water is presented in this paper,which can be used to predict humidifying deformation of loess.This method can be used to calculate the deformation of loess collapsing during infiltration.Using this method,the deformation of collapsibility of the site is calculated to be 907 mm,after being modified by 605mm.The subsidence of surface subsidence point Q3-1 is 593 mm,the settlement of surface settlement point Q 3-2 is 656 mm,the settlement of surface settlement point Q3-4 is 605 mm.The calculated results are close to the actual ones,so this method is effective in predicting the deformation of loess collapsing in the infiltration process.（5）The humidification deformation process is simulated by numerical calculation.The hydrodynamic coupling effect is taken into account in the calculation process,and the variation rule of humidification deformation with time can be obtained in the process of water infiltration.The deformation of the site is calculated to be 724 mm.by numerical simulation.The actual maximum deformation of collapsing in immersion test is 656 mm.The calculated results are close to the actual ones,so this method is effective to predict the humidification and deformation in the process of water infiltration.