Comparative analyses of geophysical methods for determining shear wave velocity of soils
The Missouri Department of Transportation (MoDOT) routinely acquires seismic cone penetrometer (SCPT) shear wave velocity control as part of the routine investigation of soils at highway structures or other geotechnical sites within the Mississippi Embayment. In an effort to ensure their geotechnical investigations are as effective and efficient as possible, the SCPT tool and several available alternatives (crosshole: CH; multichannel analysis of surface waves: MASW; and refraction microtremor: ReMi) were evaluated and compared on the basis of the interpretation of processed field data acquired at two test sites in the Poplar Bluff area, southeast Missouri. These four methods for determining the shear wave velocity of soils were subsequently ranked in terms of accuracy, functionality, cost effectiveness, other considerations and overall utility. On the basis of the comparative analyses, it is concluded that MASW data are generally more reliable than SCPT data, comparable to quality ReMi data and only slightly less accurate than CH data. However, MASW's other advantages generally make it a superior choice over the other methods for general soil classification purposes to depths of 100 ft (as per NEHRP recommendations). MASW data are much less expensive than CH data and can normally be acquired in areas inaccessible to drill rigs. MASW data are less expensive than SCPT data and can normally be acquired in areas inaccessible to SCPT rigs. In contrast to the MASW tool, quality ReMi data can be acquired only in areas where there are interpretable levels of "passive" acoustic energy and only when the geophone array is aligned with the source(s) of such energy. One other real advantage the MASW method has over the CH and SCPT methods is that it can be used to map variable depth to bedrock.