Analysis Of The Foundation Behavior In Expressway Embankment Widening

Owing to the requirements of the tremendously increasing traffic flow in the areas of advanced economy in China, the existing 4-lane expressways can no longer meet the demand. It is very urgent to widen the existing expressways to 6-to-8-lane expressways. Since the expressway widening projects are mainly distributed in coastal soft soil areas, there are relatively high requirements for controlling settlement and differential settlement. However, at present researches on foundation behavior in expressway widening projects haven't gained satisfactory systemic achievements. Combining numerical method with measurement on site in studies is an effective way to probe into foundation behavior in widening expressways.As to direct splice type of embankment widening, considering the three foundation treatment methods under old and new embankments respectively, using elastic model, the horizontal and vertical displacement fields of the foundation are calculated and analyzed in this thesis. This thesis studies and analyzes in detail how the main physical mechanics parameters of the embankment and foundation affect the maximum settlement, minimum settlement and differential settlement of the top surface of the embankment, and makes efforts to find out the governing principle. By analyzing the foundation behavior when different foundation treatment methods are adopted, it is argued that when composite foundation method is used both settlement and differential settlement of the top surface of the embankment are smaller than those when consolidation method is adopted. Using elastoplastic constitutive model, the thesis calculates and analyzes the horizontal and vertical displacement fields in the foundation when identical parameters are adopted, and sums up the underlying laws when the settlement and differential settlement of the top surface of the embankment vary with the embankment and foundation parameters. By analyzing and comparing the calculation results of the two models, it is concluded that the calculation results of the two constitutive models are quite close.In separate splice type of embankment widening, the horizontal and vertical displacement fields of the foundation are calculated respectively when isolating wall is used solely and when isolating wall with other treatment methods is used simultaneously. When isolating wall is used solely, this thesis analyzes how thesettlement and differential settlement of the top surface of the embankment vary with the physical mechanics parameters of the embankment, foundation and isolating wall. Further more, the reducing ratio of the embankment settlement as the result of the isolating wall is calculated both in homogeneous foundation and layerwise foundation under different conditions. It is concluded that in natural foundation using isolating wall can reduce the settlement of the embankment to some degree, however, when isolating wall and other treatment methods are used simultaneously, the effect of isolating wall is unobtrusive.Last but not the least, by calculating and analyzing a specific case, it shows that the calculation results obtained by using the calculation model elaborated in this thesis are quite close to the data on site and can meet the demand for practical use.