Study On Widening And Heightening Method Of Subgrade In Highway Reconstruction And Extension

With the rapid growth of economy and the increasing traffic of highway,the capacity of old highway is far from satisfying the increasing traffic.It is urgent to expand the capacity of the old highway,and the extension and reconstruction of the old highway is the inevitable trend in our country.In the early stage of the highway construction,the technical index is low.Thus,the adjustment of the longitudinal slope index and the increase of the bridge(culvert)headroom,make it necessary to adjust the longitudinal section in highway reconstruction and extension.Compared with the simple widening subgrade,the widening method,widening material,building method and differential settlement control will be more complicated when a road is widened and heightened at same time.This research project relies on the extension project of Huizhou Yantian highway(Shenzhen section).Aiming at a series of problems brought by the longitudinal adjustment of the road,the combined method of theoretical analysis and numerical simulation is used to study the widening method,deformation characteristics and influence factors of the subgrade,and the effect of subarea filling the subgrade.The main work and results are as follows.1.The advantages and disadvantages and practicability of common widening methods were analyzed,and the settlement deformation and differential settlement of unilateral widening method and bilateral widening method are analyzed by numerical simulation.The results show that the total settlement and differential settlement of the bilateral widening method are smaller than the unilateral widening method.Based on the characteristics of the extension project of Huizhou Yantian highway(Shenzhen section),it is proposed that the heightened subgrade should widened at two sides,half opened traffic and half constructed,and filled the subgrade by region.2.According to the characteristics of the project,four types of subgrade construction scheme were discussed,including light soil subgrade filling,retaining wall at medial strip,steel pile at medial strip and reinforced retaining wall at medial strip.The result shows that cantilever retaining wall can be fast constructed,and the quality was easily controlled.Cantilever retaining wall has economic advantages when the supporting height is low.The retaining measures for different height are proposed.3.Different analysis models of subgrade were established,and the effects of ground stiffness,embankment stiffness,heightening height of subgrade on deformation characteristics were studied.It is proposed that the deformation of heightening and widening subgrade can be divided into the superposition of new filled road and widening road.The results show that:(1)The widened subgrade can use fully compacted new filled soil to improve its degree of compaction modulus to reduce the non-uniform settlement.However,when the ratio of new and old subgrade modulus exceeds 1.0,the continued improvement of subgrade modulus has little effect on reducing the non-uniform settlement.(2)The settlement deformation of subgrade is greatly affected by the treatment of subgrade.When the foundation is weak,the ground treatment is very effective in reducing the subgrade settlement,but the excessive improvement of the ground treatment may lead to large settlement in the middle road,widening part is small,and the road surface forms the reverse slope.(3)The compression modulus of ground soil should be increased to reduce post-construction settlement and differential settlement when heightening height is smaller.When the heightening height is bigger,the ground stiffness should not be excessively improved to avoid reverse slope.4.Partition filling subgrade construction model is established to study the settlement in the construction stage of the half opened traffic and half constructed.The results show that subgrade filled by region will cause obvious additional settlement on another half.Due to the existence of differential settlement,the slope of road arch decreases,which may be adverse to road drainage and driving.5.The research results show that the method,material,construction technology and differential settlement control of widening meet the requirements of specifications,and the scheme is feasible.