Abstract: In order to control the deformation of subgrade under long-term traffic load, the dynamic deformation control method is employed to study the relationship between the critical height and the humidity of subgrade from the viewpoint of mechanics. Firstly, a quantitative formula of resilient modulus, humidity and compactness is obtained according to the result of laboratory resilient modulus test. Then, combining the solutions of dynamic response of the multilayered subgrade structures and the principal of compatibility of deformation between pavement and subgrade, the allowable value of dynamic deformation of subgrade top is derived. Based on the quantitative formula and the control standard of dynamic deformation of subgrade top, the relationships among the critical height, humidity and the compactness are built up. Finally, numerical results are obtained by taking two typical asphalt pavement structures for example. It is shown that, the critical height of subgrade increases with the increasing humidity. Both of the subgrade humidity and the compactness have little effect on the critical height of subgrade when the subgrade humidity is less than the optimum water content. However, when the subgrade humidity is more than the optimum water content, the critical height of subgrade increases sharply with the increasing humidity; and the effect of the compactness on the critical height becomes significant. The results provide a new idea for reasonable value of the subgrade height and humidity.

Key words: dynamic deformation control, long-term traffic load, multilayered road structure, critical height of subgrade, subgrade humidity