Experimental Study On The Characteristics Of Vertical Compression-Rebound Of Q3 Loess

Loess is a special structured soil,and it is widely distributed in China.The compression-rebound characteristics of the soil directly affect the practical application of the project,such as the excavation of foundation pits and tunnels in the construction of infrastructure.At present,there are many studies on the compression characteristics of loess,but there are relatively few studies on the whole process of compression-rebound of loess and the effeect of structure on compression-rebound characteristics.Therefore,in this paper,the Q3 loess near Hansenzhai in Xi’an City was used as the research object,conducting experimental research about the vertical compression-rebound of the undisturbed,reshaped and undisturbed saturated loess with different water content and different dry densities,using a double-linked high-pressure consolidation instrument.The main results and conclusions obtained are as follows:(1)The variation law of vertical compression-rebound curve of loess at different depths is basically the same.During compression,the soil is compacted,and the void ratio decreases with the increase of the axial pressure;during unloading,the soil is rebounded,and the void ratio increases as the axial pressure decreases.The greater the moisture content of the loess,the greater the compression and rebound deformation;the greater the dry density of the loess,the lower the compressibility,and the dry density has less influence on the rebound deformation of the soil than the compressibility;with the pressure increases,the soil becomes larger.(2)The greater the consolidation pressure on the soil sample,the greater the resilience of the soil after the rebound is completed;0.5 and 0.75 are regarded as the critical unloading ratio and the limit unloading ratio of loess at this site after analysis;the rebound modulus of the soil is not a fixed value,and the resilience of the soil is different,and its rebound modulus is also different;and under the same unloading ratio,the soil with higher consolidation pressure has a higher rebound modulus(3)The time-history curve of resilience deformation of loess is consistent with the time-history curve of re-resilience deformation of loess.With the increase of the total unloading amount,the soil gradually produces springback deformation during the stabilization time.There is obvious hysteresis in the springback deformation,and the unloading ratio is most significant between 0.9-1.0(4)Under the same pressure,the compressive strain of remodeled loess>compressive strain of saturated undisturbed loess>compressive strain of undisturbed loess;and the soil with lower dry density has larger structural parameters(5)The relationship between structural parameters and axial pressure is obtained Regardless of whether the loess is in the rebound stage or the re-rebound stage,its structural parameters increase rapidly with the increase of the load.When it reaches a certain value,the structural parameters suddenly decrease and gradually stabilize with the increase of the load(6)It is obtained that the compression coefficient of loess decreases with the increase of structural parameters,and the rebound modulus increases with the increase of structural parameters in a certain load range.