Study On The Permeability And Mechanical Properties Of Loess At The Mesoscopic Interface With Root System

The micro interface of loess is a structural defect widely distributed within the loess body,and it is also a poor control surface that induces geological disasters.It is an important factor in controlling loess disasters.The loess micro interface formed by plant roots is one of them,which refers to the root channels formed by the development of plant roots in loess,as well as the expansion cracks formed under the action of root splitting.Studying the formation and evolution process of plant root micro interfaces,as well as the strength and permeability characteristics of loess samples containing root micro interfaces,will have certain research significance in revealing the catastrophic effects of root micro interfaces.In this paper,taking the loess in the Southern area of Jingyang County,Shaanxi Province as the research object and conducts CT scanning tests on root meso interface loess samples,as well as uniaxial compression tests and permeability uniaxial compression tests.The main research results are as follows:(1)The formation and evolution process of the microscopic interface of the root system includes three stages:(1)the tip of the root system enters the soil pores,and the pores are connected;(2)The volume of root development increases,squeezing surrounding soil particles,and the interface expansion stage;(3)The root system continues to develop,repeating stages(1)and(2),and the micro interface of the root system continues to expand.(2)CT scans were performed on three types of loess samples: remolded,undisturbed,and deposited.The image processing results showed that the development direction of the root micro interface of the remolded soil sample had an angle of nearly 90° with the horizontal plane.After the soil sample was loaded and damaged,the interface position shifted and cracking and expansion occurred;The development of the root micro interface in the undisturbed loess sample is influenced by factors such as calcium binding,and the development direction is irregular.After loading,damage occurs at the original micro interface;The angle between the micro interface of the sedimentary loess sample root system and the horizontal plane is nearly 90°,and the upper part of the interface disappears after loading failure.Extracting equielliptical region data from two-dimensional CT slices,it was found that the development of root micro interfaces compresses the soil on both sides,resulting in a decrease in the density of material points inside the interface and an increase in the density of material points outside the interface.(3)The spatial distribution of the root meso interface controls the water transport path of preferential flow,and its length and quantity control the maximum infiltration depth and staining ratio of bright blue solution.The more and longer the meso interface,the greater the water infiltration depth and staining ratio.(4)Under uniaxial compression conditions,the stress-strain curves of the specimens containing root mesoscopic interfaces mainly exhibit extremely strong softening and strong softening types.The deformation mode is mainly axial deformation,and the failure mode is brittle failure and brittle plastic failure.After infiltration,the stress-strain curve of the micro interface sample containing the root system mainly shows a softening type,with axial deformation as the main deformation mode and plastic failure as the main failure mode.The larger the length and quantity of the root micro interface,the more failure surfaces and the larger the scope of failure.The relationship between the failure surface and the micro interface tends to overlap.