Research On Effects Of Widing High-Grade Way On Subgrade Deformation In Seasonal Frozen Area

The key issue is the deformation of widening subgrade of high-grade way. It affects the life-span of the widened highway and driving comfort. As the area of seasonal frozen soil is more than half of the total land area in China, research on influence of widening in high-grade highway of seasonal frozen area on the deformation of subgrade makes a particular theoretical and practical significance on fully considering the influence of seasonal freezing-thawing in widening engineering, controlling the whole stability and asymmetrical settlement of new and old subgrade effectively, reducing the resulting cracking and damage of the layer on upper pavement,decreasing the management and maintenance costs, ensuring project quality and maintaining a good driving condition.The issue, the intensity indicators and variation laws of shear strength of subgrade soil under different conditions, deformation features of widening subgrade in test sections, deformation features of widening subgrade under different engineering conditions etc., had been studied with laboratory tests, regression calculations, theoretical analysis, on-site monitoring, numerical simulation methods etc., with expansion project of Tongsan highway from Fangzheng to Harbin in China.Its main duties include research on engineering properties of subgrade soil, variation laws of the intensity indicators of subgrade soil after freeze and thaw, study of Mathematical Model, data analysis of on-site monitoring, numerical analysis of deformation of widening subgrade under different conditions, the main research contents and results are as follows:(1) The results, the recommended value of compaction standard of widening subgrade and concluded that the law on the influence of the changing in moisture content, degree of compaction on the strength index of subgrade soil, strength index and the laws of shear strength of the subgrade soil with different properties of the geogrid and the interaction laws of shear stress, shear displacement, normal stress and the percentage of water content in the reinforcement-soil interface to determine the finite element parameters for the need of further analysis, had been achieved by the test analysis in the laboratory.(2) Triaxial test results of freeze-thaw cycles show that with the increase in the number of freezing and thawing, soil cohesion decreases and the internal friction angle increases, but it increases significantly smaller, under the same degree of compaction cohesion of the soil with high percentage of water content has a bigger drop. The regression equation of a cohesion c, friction angleφof subgrade soil in freezing and thawing had been build by the MATLAB mathematical analysis software to regress the test data, it can be used to predict strength index of subgrade soil in freezing and thawing. (3) The results, layer deposition is in a significant acceleration process in the stratified filling process of widening subgrade, the lateral deformation, pore pressure and earth pressure are also increasing. After the filling construction of new subgrade, earth pressure is stable, in the consolidation process of soil, water pressure of excess pore has a significant dissipation. Under the effect of the new fill subgrade soil, differential settlements between the old and the new subgrade occur, with the increasing of filling rate, the settlement rate increases, the growth rate of lateral deformation is faster, the depth of maximum lateral displacement in the toe of new fill subgrade is larger than it in the shoulder of old roadbed. When consolidation settlement of soil basically completes, the subgrade and foundation are in a relatively stable state, the settlement of the new and old roadbed is slow, differential settlement rate is basically stable, had been achieved by test monitoring on stratified settlement of widening subgrade, horizontal displacement, pore pressure and earth pressure of the observation section in the test section.(4) The finite element had been used to simulate the on-site construction by required parameters for finite element through the laboratory test of subgrade soil. The result, calculated results of the horizontal deformation and vertical deformation at different depths in the new roadbed shoulder, at the combination of the old and new subgrade and the old roadbed shoulder are consistent with the measured values and they reflect the same law, had been shown.(5) The finite element had been used to simulate numerical values in six kinds of different conditions, such as, the widening ways, excavation and filling of steps, filling height, filling rate, using geogrid, freezing and thawing. It had been analysed that the deformation features of widening subgrade is impacted by the different conditions, especially for comparative study of combination of new and old subgrade, the new subgrade shoulder, the toe of new subgrade, the top of the widened subgrade, foundation outside the toe of new subgrade and so on typical location. The deformation laws of widening subgrade had been found under different conditions and influential factors.In order to effectively controlling deformation and preventing landslides and facilitating the construction works considerations, according to the finite element analysis, the recommendations of height 100cm, width150cm excavation reclamation methods had been determined. In order to effectively reducing the vertical deformation and lateral deformation of roadbed, the way that Laying two layers of geogrid at the bottom of the foundation can be used to it. In order to reducing the influence of freezing and thawing on the security, the recommended value of compaction degree can be used to control moisture near best moisture. It had been provided by this article about compactness standard distributing with the subgrade height of widening subgrade.