Study On Deformation Characteristics Of Aeolian Sand And Reinforced Aeolian Sand Subgrade Of Menghua Heavy-load Railway

There is a large area of desert land in the arid and rainless western region of China.Aeolian sand is the main roadbed filler in the construction of highway and railway in the desert area.The MHTJ-2 section of Menghua Heavy-load Railway crosses the southern margin of Maowusu Desert.Due to the lack of high-quality roadbed filling in this area,the coarse-grained soil filling needed is pulled from Ningdong area more than 100 kilometers away.Therefore,the local rich aeolian sand is used as the filling under the roadbed bed in the design.Based on the engineering practice,typical sections are selected as test sections,and the engineering characteristics of aeolian sand filling and the deformation characteristics of aeolian sand and reinforced aeolian sand subgrade are studied by means of literature review,laboratory test,settlement observation and numerical simulation.The main research contents and related research results are summarized as follows.?1?The natural aeolian sand samples in Maowusu desert were selected for indoor geotechnical tests.The particle size is mainly distributed in the range of 0.075 mm to 0.25mm,the specific gravity of the particles is between 2.63 and 2.67g/cm³,the natural moisture content is between 1.54 and 1.59g/cm³,the inhomogeneity coefficient Cu is between 1.94 and2.01,and the curvature coefficient Cc is between 0.99 and 1.01.According to the specifications,it belongs to the poor graded C3 group fillers.The contents of SiO₂,CaO and Al₂O₃ in the samples accounted for more than 80%of the total contents,and their pH value was about 8,which was weak alkaline and non-saline soil.The maximum dry density is1.79g/cm³ and the optimum moisture content is 14.23%.The compaction curve is inverted"S"type.When the compactness of aeolian sand is 0.95,the internal friction angle is 39.5degrees and cohesion c is 0.5 kPa in the natural water content state?w<1%?,and the internal friction angle is 34.8 degrees and cohesion c is 13.5 kPa in the optimum water content state?w=14.23%?.?2?The development law of aeolian sand foundation settlement in the test section can be divided into three stages:initial slow increase,medium-term rapid development and final stabilization.On the same section,the settlement of the foundation under the shoulders on both sides is small,the settlement below the track center line is large,and the overall settlement trend is"concave".?3?The settlement prediction results show that the settlement of aeolian sand foundation mainly occurs within 18 months after the completion of roadbed filling,accounting for about80%of the final settlement.Two years after the completion of roadbed filling,the settlement has been basically completed.?4?The results of numerical simulation show that the vertical stress of the roadbed is basically saddle-shaped distribution on the cross section of the roadbed;when no reinforcement is applied,the maximum vertical displacement of the bottom of the roadbed filled with cement-modified aeolian sand and physical-improved aeolian sand is similar;when there are slope reinforcement and slope protection measures,the vertical displacement of the top of the roadbed decreases by about 1.3%,indicating that geogrid reinforcement effect is obvious;in the desert area of Heavy-haul Railway Subgrade engineering,reinforced aeolian sand can be used instead of physical improved aeolian sand as subgrade bed bottom filling.?5?The research results can provide guidance for engineering design and construction of Aeolian Sand Subgrade in the whole tender section,and provide reference for similar projects in this area.