During the inspection of compaction quality for highway roadbeds or railway trackbeds, theselection of a spot for the plate bearing test (PBT) or field density test may frequently invokeconflicts between the construction inspector and construction manager. Furthermore, ifcompaction quality is not acceptable, a judgment on whether it is attributed to poor material orpoor compaction efforts is not straightforward. Consequently, specifications on compactionquality based on a one-point method such as the PBT and field density test would not be arational approach. As an alternative to the one-point method, this paper proposes a nondestructivesurface-wave technique for a spatial distribution of surface-wave velocity (or shearwavevelocity) of compacted material as compaction quality in two dimensions to eliminate theconflicts involved in selecting a test spot. The proposed technique, called the impact-sourceCSW (ICSW) method, evolved from the conventional continuous surface wave (CSW) method.ICSW method incorporates an impact source rather than a harmonic-signal vibrator. Also, itadopts a new analysis algorithm called the wave-number unwrapping technique, developed toovercome the inherent limitation of the conventional CSW method. To verify validity andfeasibility of the proposed ICSW method, field applications were made to construct a 2-Dstiffness profile of compacted subgrades and comparisons were made between Young’s modulifrom ICSW tests and subgrade reaction coefficients from PBT.
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