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Abstract Based on the classical Boussinesq analytical solutions，a set defined by stress and strain state of points，when subjected to concentrated load，with varied spatial location in semi-infinite elastic subgrade and constrained by certain conditions，is employed to characterize the stress and strain state of a fixed point in the subgrade during the loading-unloading process induced by a single vehicle load. Dynamics，consequently，is transformed into quasi-statics，and analysis model，which is supposed to be convenient and practical for verifying subgrade dynamic behaviors，is established. Stress state and effective working radius are approached and determined during a loading—unloading process in subgrade. Results indicate：(1) curves of dynamic normal stress differences( ) and ( ) are pulse shape，while( ) changes in a twin peak manner；(2) the maximum principal stress might whirl abruptly about z axis，and the angle intersected with z axis rotates gradually and continuously by 180°；the orientation of minimum principal stress turns in a relatively smooth pattern and its rotation features are less remarkably；while the intermediate principal stress direction alters elusively；(3) effective working radius，which represents the limit of impacts exerted by a single vehicle loads on subgrade，pavement system，is suggested to a length of 10 m，and the influenced area can be considered as a semi-sphere with a radius of 10 m and whose center sited at the point of load. At last，the validity of effective working radius，which is defined by 10 m under one vehicle loading，is specified by in situ monitoring data.
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Received: 20 May 2011
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2011, Vol. 30 
