Road construction and maintenance are major parts of geotechnical engineering that deal with the stiffness of natural or manmade ground materials. At the earliest stage of new road construction, the ground along the planned route often needs to be characterized in terms of the overall stiffness of the overburden-bedrock system. During construction, multiple stages of compaction and grading of geotechnical materials occur, with each requiring stringent quality control processes to ensure necessary stiffness levels are achieved. After construction, it is often necessary to periodically monitor stiffness conditions underneath an existing road for development of underground subsidence, especially if the road was built over subsidence-prone areas. Traditional approaches to stiffness evaluation — for example, cone penetration tests and standard penetration tests — provide local results that are highly dependent on test location. A seismic method, on the other hand, can provide a macroscale evaluation of a given material's elastic properties. The multichannel analysis of surface waves (MASW) method provides information on shear-wave velocity, which is the most scientifically accurate indicator of material stiffness from an elasticity perspective. Because of the strong nature of surface waves, the MASW field survey becomes a highly tolerant operation and is almost always guaranteed to be effective, rendering the approach highly convenient and reliable. Subsequent data analysis procedures are straightforward and do not require the application of signal-enhancing techniques. Because subsurface velocity models can differ by type of application, corresponding dispersion patterns must be noted during the analysis. Case studies executed during the beginning and ending stages of road construction and during the maintenance stage of a built highway are presented.

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