Investigation On Deformation And Stability And Treatment Method Of Widening Subgrade

In order to meet the demand of increasing traffic volume,subgrade widening has been an effective solution with priority.In view of the subgrade widening may encounter many engineering problems during construction and operation period,it is of great significance to study the deformation and stability as well as relevant treatment method of the widened embankment under the action of traffic load and rainfall.Both numerical simulation and theoretical analysis are performed based on actual projects.The main contents and results are presented as follows.Firstly,the dynamic response of the widened embankment under asymmetric traffic load has been analyzed by the numerical model established by FLAC^3D.The traffic load is simplified to be half-sine wave.The results show that laying geogrids in the junction of widened embankment can effectively decrease the horizontal displacement,and the maximum tensile stress occurs at the bottom of the geogrid,which has mobilized its tensile strength to a greater extent.The parametric study shows that the closer the old/new embankment fill and the degree of compaction are,the smaller the differential settlement is.When the loading frequency is the same as the natural frequency of the subgrade,resonance occurs and the dynamic stress of the subgrade reaches the peak value.Secondly,based on the theory of unsaturated seepage,the simulation of rainfall infiltration has been realized by the FLAC^3D seepage module using the FISH language.The influence of rainfall infiltration on the seepage and stability of the widened subgrade is analyzed.The results show that the matrix suction on the subgrade surface decreases rapidly in the early stage of rainfall,and the horizontal stress changes greatly.The stress concentration occurs at the junction of old/new subgrade and the slope toe.The plastic area of the reinforced condition is obviously smaller than that of the unreinforced case when the slope is instability.The stability of the subgrade can be effectively improved by setting reinforcement in the junction.Thirdly,the effect of three kinds of treatment methods,including laying geogrid in the junction,using lightweight fill and composite foundation,has been compared by numerical simulation aiming at the differential settlement of widened subgrade in soft soil area.Two cases,the weak soil under the old subgrade is untreated or treated,have been considered.The results show that laying geogrid in the junction is only suitable to the subgrade widening project on the soil of low compressibility.The methods of using lightweight fill and composite foundation can obviously reduce the differential settlement of the widened subgrade in the soft soil area.