Analysis On Dynamic Response Of Soft Clay-Composite Foundation Under Transportation Loads

With the rapid development of national economic, highway of normal level has satisfied the great need of transportation business. So, many freeways have built recently because of their advantages. And also because of high speed of vehicle and heavy traffic, contrast to highway of normal level, higher requests are posed for the pavement and ground. Restricted by geography position, many freeways have to be built on the soft-soil ground. Because of low intensity, high compressibility, low permeability and rheology of soft-soil, technology of freeway construction becomes more difficult and complicated. From the investigation about running of freeway, settlement of embankment after work are universally considerable. The deformation and settlement of pavement under traffic loads are the problem which is concerned about all along, and also a project to be studied deeply.In this paper, the characteristics of transportation loads are introduced firstly, and then movable invariable load and stable simple harmonic load are decided on as the simulation of transportation loads. Secondly, the dynamic characteristics of soft-soil composite ground and status of study on them at present are expounded. At last, the project to be studied is simplified as a problem of plane-strain, and using both linear-elastic model and elastic-plastic model, transient response of composite ground under transportation loads are analyzed with FEA method. The main contents are as the following:1. Viewing the cross section of subgrade as the studying target, traffic load is simplified as half-sinusoidal load. Firstly, considering the precision and costs of numerical computing, the incidence of load in the foundation is specified by calculation and the relation between load cycle and vertical displacement of road surface is studied. Then, transient response of vertical displacement, vertical stress and pile-soil stress ratio of some nodes in the elastic subgrade are computed in one single load cycle. Finally, regarding height of embankment as parameter, considering time-variantion of clay, the transient response of stress and displacement of nodes in the elastic-plastic subgrade and the permanent settlement of road surface are computed, so that the influence ofheight of embankment on settlement of road surface is analyzed. 2. Viewing the lengthwise section of subgrade as the studying target, traffic load is simplified as mobile invariable load. Firstly, transient response of vertical displacements vertical stress and pile-soil stress ratio of some nodes in the elastic subgrade are computed under mobile invariable load with pile-soil analysis method and composite-module method respectively, and the results obtained with the two methods are compared and analyzed. Then, seeing the velocity of vehicle and height of embankment as variants, settlements of surface of elastic-plastic subgrade under mobile invariant load are computed, and the influence of velocity of vehicle and height of embankment on settlement of road surface is analyzed. The method and results of this paper will provide certain theoretical method andreference for continuous research on dynamic response of soft clay-compositefoundation under transportation loads in future.