Accelerated stiffness profiling of aggregate bases and subgrades for quality assessment of field compaction

As a compaction control parameter, stiffness has been investigated as an alternative to dry unit weight, because the design of pavement is based on the elastic modulus of pavement layers. A reliable and practical quality assurance system was proposed to accelerate the quality assessment of field compaction. The proposed system, which has evolved from the spectral analysis of surface waves (SASW) method, profiles the shear wave velocity of the unbound aggregate base and subgrade. The system consists of dedicated hardware for surface wave measurements and an analysis algorithm to automate the interpretation and analysis procedures. The measurement hardware consists of two sensor units and one source unit and can be operated by one person. The automation in interpretation and analysis was implemented with the peak-trough method and the frequency wave number technique. Consequently, the surface wave measurement for stiffness profiling is reduced to a 10- to 15-min task. The validity of the proposed hardware and algorithm was verified by a comparison of the results acquired by the conventional SASW measurements with the results acquired by the accelerated SASW system. Twenty-one subgrade and 11 base sections were selected at three pavement construction sites and tested with the accelerated SASW system, the dynamic cone penetrometer (DCP), the plate-bearing test, and the falling weight deflectometer (FWD). Results indicated that the shear wave velocity predicted by the accelerated SASW system showed a favorable agreement with DCP index at both subgrades and bases. Young's modulus evaluated from the shear wave velocity also agreed roughly with the FWD modulus and subgrade reaction coefficients.