Study On The Characteristics Of Improved Loess Collapse And Numerical Simulation Of Seepage Erosion In Loess Roadbeds

The extensive development of subsurface erosion in the loess region is mainly due to the large pores and joint fissures of loess,which can lead to dominant seepage and significant disaster effects.The potential erosion of loess poses a serious threat and damage to highway embankments in loess areas,as the underground dynamic water during the thesis erosion process is the main cause of roadbed settlement and hidden holes.This paper studies the problem of soil erosion in loess embankments from two aspects.One is to determine the foundation treatment methods that are beneficial for improving the resistance to soil erosion through different improved loess collapse tests,and the other is to apply numerical simulation to study the main influencing factors of soil erosion in embankments.Based on the above two aspects of research,the main research content and conclusions of the thesis are as follows:(1)A disintegration test was conducted on improved and reshaped loess samples equipped with sample preparation to observe the occurrence of disintegration phenomenon and analyze the development law of soil disintegration.The observation results indicate that the order of improvement effect on the resistance to collapse of improved loess is from large to small: cement,lime,polypropylene fiber;After 7 days of curing,the cement modified loess sample with a compaction degree of 0.85 did not experience disintegration;After 14 days of maintenance,the lime improved loess sample with a compaction degree of 0.85 did not experience disintegration;As the compaction degree of loess samples increases,the disintegration rate and disintegration rate of polypropylene fiber modified loess samples show a decreasing trend.Obtain the basic physical properties,permeability coefficient,and shear strength indicators of loess through geotechnical tests,providing corresponding parameters for subsequent numerical simulation of loess roadbed.(2)This thesis is based on the theory of unsaturated soil mechanics,combined with the concept of "air unit",and takes loess roadbed with a single crack as the research object.The COMSOLMultiphysics finite element software is used to establish a seepage model of unsaturated loess roadbed with a single crack under the condition of underground drainage pipeline damage and leakage.By discretizing the soil matrix and cracks of loess roadbed into finite elements,a numerical model was established that can effectively analyze the flow exchange between cracks and matrix in loess.(3)We simulated the infiltration of water into the roadbed soil under the condition of underground drainage pipeline damage and leakage,and studied the influence of seepage on the volume moisture content and pore water pressure of the roadbed.The results indicate that as the infiltration time continues,water preferentially flows along the cracks and can quickly penetrate the cracks,slowly advancing through the matrix soil;As the depth of the roadbed increases,the infiltration capacity of the water gradually weakens;The increase in infiltration intensity causes the wetting peak to accelerate downwards.(4)Based on the above research,by considering four factors: saturated permeability coefficient,crack width,groundwater level,and infiltration strength,the variation law of volumetric moisture content under different parameter factors is calculated and analyzed,and the leakage situation of unsaturated loess roadbed pipelines containing a single crack is studied.The results indicate that increasing the saturated permeability coefficient significantly accelerates the seepage process of the roadbed compared to the crack width,and causes the volume water content at the crack to decrease with the change of infiltration time.In addition,the change in initial moisture content will also affect the water storage capacity of the soil,resulting in an increase or decrease in volumetric moisture content when the water infiltrates to a certain depth.The leakage strength of underground drainage pipelines has an impact on the infiltration rate and amount of fractured loess roadbed.If the infiltration capacity of the fractured loess roadbed is exceeded,the remaining water will flow along the inner diameter of the underground drainage pipeline.