Structural Design And Differential Settlement Analysis Of Abutment Approach Filled With Lightweight Soil

The phenomenon of abutment bump not only affects the comfort and safety of expressway driving,but also increases the maintenance cost of expressway later,it has become a key problem that needs to be solved urgently at bridge approach.The root of the phenomenon of abutment bump is differential settlement.Domestic and foreign research and a large number of engineering applications have shown that foam lightweight soil can effectively reduce differential settlement at bridge approach.Therefore,foam lightweight soil has a good application prospect at bridge approach.At present,many scholars have studied the differential settlement at bridge approach filled lightweight soil,but less studies the impact of construction period time on post-construction settlement,and in practical engineering applications,there are no uniform standard for the target density of lightweight soil and structure type at bridge approach.Based on the project of Zhanhua-Linzi Expressway in Shandong Province and considering the impact of construction period,the differential settlement of bridge approach is analyzed by numerical simulation and theoretical calculation.Firstly,road-bridge transition model is established by ABAQUS,and the differential settlement of transition section is analyzed from four aspects:lightweight soil material,structure type of transition section,subgrade height and construction period.Then,the Layer wise summation method is used to calculate the foundation settlement of bridge approach based on the results of numerical simulations,and the post-construction settlement of the subgrade surface under different construction periods is obtained by using Terzaghi consolidation theory.The main research conclusions are as follows:(1)Under the principle of differential settlement control and cost control,the structure type of transition section of lightweight soil is optimized by selecting 5m basement length and 1:2 step slope ratio;(2)The factors affecting the post-construction settlement of bridge approach of the lightweight soil are in order of importance:construction period time,roadbed height,lightweight soil material density,structure type,and lightweight soil modulus;(3)Compared with conventional filling,the use of lightweight soil can effectively reduce the settlement of the foundation at abutment approach,and the greater the height of the roadbed,the more obvious the treatment effect;(4)The contrast of the consolidation calculated by the three methods of instantaneous loading,primary linear loading and quadratic linear loading,indicate that it is more accurate to calculate the foundational consolidation of abutment approach by using the quadratic linear loading method;(5)Based on the foundation conditions of Zhanlin Expressway,the height of the subgrade is 6m,it is recommended to choose lightweight soil with a density of 0.6～0.8g/cm3 for abutment approach,and the time for the static load preloading of subgrade before pavement construction shall be controlled within 240d～360d.If the density of 0.8～1.2g/cm3 is selected,it is recommended to treat foundation and shorten the time for the static load preloading to less than 360d.If the height of subgrade is more than 6m,it is recommended to adopt combined foundation treatment with lightweight filling.