Study On Engineering Characteristics Of Unsaturated Silt Subgrade In Drying And Wetting Cycle

Parts of Henan province is located in the Yellow River flood plains, where silt iswidely applied as subgrade filling material. Embankment settlement disease such aspost-construction settlement, pavement structure destruction is becoming much moresevere because of the growing road traffic flow, the increasing proportion ofoverloaded vehicles, bad engineering properties of silt, which increases costs of roadmaintenance and repair. In this paper, in view of the silt roadbed settlementdeformation problem, mechanical properties of silt were systematically studiedthrough indoor experiments on the basis of the understanding of relevant research athome and abroad. By using drying-wetting cycles tests to investigate the effect on thedeformation characteristics of unsaturated silt, followed by large-scale finite elementanalysis software ABAQUS simulation to study settlement and deformationcharacteristics, a series of important data was generated as theoretical reference forthe settlement control in the engineering design and construction.Results:(1) By GCTS test, soil-water characteristic curves were got under three kinds ofcompaction degree, and fit with the Van Genuchten model and Fredlund-Xing model,it was found that Fredlund-Xing model fitting effect is better as it can reflect steepfall of soil-water characteristic curve in the transitional period of silt. With theincrease of the degree of compaction, the slope of soil-water characteristic curve oftransition curve became slightly slower, which showed that samples were morecompact, and water flew more difficult in the soil sample, more conducive to thestability of the silt roadbed compaction degree.(2) Based on five dry-wet circulation after the engineering properties ofunsaturated silt, it is observed that under the same load, after1dry-wet circulation,the strength and deformation parameters of silt samples were significantly smaller, i.e.the soil strength and resistance to deformation ability reduce. After dry-wetcirculation of many times, the engineering properties of soil samples tended to basicstable. Therefore in the silt subgrade design, strength and deformation parameters aremore reasonable to use the dry-wet circulation after many times. (3) The matrix suction has certain influence on failure forms and peak strengthof silt samples. Stress strain curve will be strain hardening model under the conditionof low suction, while is characterized by strain softening under high suction, whichshows that "brittle" nature of silt samples become more obvious with the increase ofmatrix suction. The effects of matrix suction on silt shear strength, silt peak intensitymonotonously increases with the increase of matrix suction when matrix suction is nomore than200kpa.(4) Compared with saturated silt samples, cohesive force significantly increasewith the increase of matrix suction, while internal friction angle of approximatelyequal to the angle of internal friction in the saturated sample. This shows that theinfluence of matrix suction on unsaturated silt strength parameters are mainlyembodied in the cohesive force c.(5) Nonlinear finite element calculation model was established considering siltroadbed of asphalt pavement structure and by using ABAQUS software, and thedifferent time of dry-wet circulation influence on pavement structure deformation wasmainly analyzed, which has a certain reference value to the silt subgrade pavementstructure design.