Research On The Interaction Between New And Existing Embankments And Treatment Techniques In Highway Widening Engineering

With the rapid development of economy, the traffic volumes of expressway are rapidly increasing. A considerable number of expressways in service are no longer satisfy the need for both increasing traffic volumes and social progress, thus more and more highways are pending to be reconstructed or widened. The expressway widening is an important issue starved for solving in highway construction. Combined with the widening of Nanjing belt highway, the interaction between new and existing embankments and treatment techniques for widening on soft soils are systematically researched by methods of in-site test, numerical simulation and theoretical analysis in this paper. The main work and conclusions can be given as follows.(1)By selecting some representative sections , the changing law of engineering properties of ground under old and new embankments is explored. The in-site test shows that the properties of physical mechanical of soils under old and new embankments are both improved with an extended period time of consolidation, especially the compress and strength index of soft soil are remarkably enhanced. By comparison, the improvement under the old embankment is significantly more than that under the new.(2)The finite element method using Mohr-Coulomb elastic-plastic model is applied to the analysis of interaction mechanism between the old and new embankments in the expressway widening on soft soils during the construction and operation. The results demonstrate that the mode of widening, method of construction, construction disturbance and vehicle load have great impact on the engineering behavior of old and new embankments.(3)Based on the analysis of stress-strain behavior of old and new embankments, the rule of settlement of the embankments widening is discussed. Moreover, according to the requirements for performance of pavements and stability of embankments, the settlement control criterion of the expressway widening is presented, that is, the differential settlement between old and new embankments, total settlements and post-construction settlement of new embankment should be considered in the design of expressway widening.(4)According to the determined settlement control criterion, the appropriate methods of soft ground improvement for expressway widening are investigated, and the composite foundation method is found that is an optimal one by comparison. Further analysis indicates that the column space, column rigidity, cushion modulus and improvement area have different degree influence on differential settlement between old and new embankments. Then, Based on the analysis, the optimal design method is proposed.(5)On the basis of failure mechanism of joint of the old and new embankment, the treatment measures of the joint and the effect of improvement are studied. The results find out that the old embankment sideslope with benches and the geosynthetics reinforcement are valid for reducing the differential settlement between old and new embankments, and the width of benches and the rigidity of geosynthetics are the main factors. At the same time, the properties of the embankment fills also have a certain extent effect on the overall stability of embankments.(6)The in-site observation is carried out in NanJing belt highway widening to validate the rationality of former study. The results confirm that the former analysis on the interaction between new and old embankments and the law of settlement of embankment widening are reasonable. And the settlement control criterion, soft ground improvement methods and the connection measures for embankment...