Physical And Mechanical Properties Of Saturated Soft Loess Before And After Precipitation

The special sensitivity of loess to water action is the basic property that distinguishes loess from other soil layers.Loess in saturated state generally has two kinds of characteristics.One is that the structure of the loess is completely compacted after immersion,forming the compacted saturated loess.The other is that the structure of the loess is not completely destroyed after being immersed in water,forming the uncompacted saturated loess,which is often referred to as the saturated soft loess in engineering.The physical and mechanical properties of the saturated soft loess are significantly different from those of the collapsible loess and the saturated compacted loess.At present,precipitation scheme is mostly adopted in saturated soft loess region to ensure the smooth progress of the project,but in the concrete implementation process,a series of risk events have been caused due to the unclear understanding of its nature.In order to solve this problem,this paper takes the typical saturated soft loess in Xi ’an area is taken as the main research object.By distinguishing two sedimentary ages（Q₃ and Q₂ upper part）,using the main means of microstructure test,indoor test and in-situ test,this paper studies the saturated soft loess under four states（immersed in saturated,saturated state,after precipitation,water level rising stage）The physical and mechanical properties of saturated soft loess are studied to realize the whole process of physical and mechanical properties.This paper mainly obtains the following research results:（1）Compared with the saturated loess deposited in the same age,the saturated soft loess and the saturated Q₂ loess（soft plastic）have the characteristics of large porosity ratio,high water content,low saturation,asthenic plastic and high sensitivity.It has the mechanical characteristics of medium and high compressibility,low bearing capacity,low strength and easy to disturb and destroy.The uncompaction state and water content state are the key factors affecting its physical and mechanical properties.（2）The saturated soft loess is mainly composed of large and medium pores.In the precipitation project,the drying effect is good and the strength increases effectively.In the first three months of precipitation,it drains rapidly and then slowly,and the collapsibility can be recovered.Saturated Q₂ loess（soft plastic）is mainly composed of medium and small pores,and its drying effec is moderate in precipitation engineering.After precipitation,the saturated Q₂ loess（soft plastic）still has the typical characteristics of High water content and easy deformation characteristics,and its bearing capacity,strength and deformation resistance have not increased significantly.（3）The compaction deformation of saturated soft loess continued to occur before and after the water level rise.After the water level rises,the saturated soft loess can be formed again,or the saturated loess may be formed.The single reciprocating process of water level is not a sufficient condition for the complete compaction of saturated soft loess.Under the existing hydraulic conditions,the subsidence deformation will not occur in the process of water level rise.（4）Overburden is the main factor affecting the formation of saturated soft loess after the collapsible loess is immersed.The larger the pore ratio of collapsible loess is before infiltrating,the larger the pore compaction ratio is in the process of infiltrating.