A simple method for predicting the traffic load induced settlement of low road embankment on soft subsoil is proposed. The traffic load induced dynamic stress in the subsoil is calculated by multi-layer elastic theory. Then the plastic vertical strain in subsoil is calculated by an empirical equation, in which the constants are related to the physical and mechanical properties of subsoil. The method was applied to analyze a 1.0 km long test section of low road embankment on the soft Ariake clay deposit, Saga prefecture, Japan. The test section had 11 subsections with different construction methods. Four (4) of the subsections were analyzed in this study. It shows that the prediction agreed with the field data reasonably well, and the proposed method is useful for design the road with low embankment on soft subsoil. For the case studied, the depth significantly influenced by traffic load is about 6 m below the base of the embankment. The analyses together with field data indicate that increasing the thickness and stiffness of the subgrade is very effective for reducing the traffic load induced permanent deformation of soft subsoil.


For low road embankments (less than 3.0 m high) constructed on soft subsoil, the permanent deformation of subsoil due to traffic load controls the design life as well as the maintenance costs. To select a cost effective design, it is desirable to predict the traffic load induced time dependent settlement. Although some methods have been proposed to calculate the traffic load induced settlement, a rational and simple method is not available yet. Several factors affect the traffic load induced deformation, namely,

  • the strength and deformation characteristics of the subsoil,

  • the properties of the pavement and subgrade of road, and

  • the magnitude and number of applications of traffic load.

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