A Case Study of Multichannel Analysis of Surface Waves (MASW) as a Tool to Characterize Unknown Foundations-Paper

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This case study evaluates multichannel analysis of surface waves (MASW) as a noninvasive method for identifying the geometry of an unknown bridge foundation. MASW estimates subsurface stiffness from surface-wave velocities, offering a rapid alternative to costly excavation or borehole testing.<br /><br />Researchers surveyed a bridge foundation in Philadelphia and a nearby control area. The foundation comprised a concrete pile cap supported by 35 battered, cast-in-place piles. Using a 24-channel seismograph, they recorded surface waves generated by sledgehammer impacts and inverted the resulting dispersion curves to estimate shear-wave velocity profiles.<br /><br />The profile measured over the foundation showed stiffness increases of approximately 15% near the pile cap and about 35% at greater depths compared with the control profile. Changes in the raw waveforms also indicated a near-surface foundation width of about 5 m, reasonably close to the known 7.3 m dimension. These results suggest MASW can detect substantial foundation-related anomalies.<br /><br />However, the method’s depth of investigation was limited by the wavelengths recorded. The study estimated the foundation bottom at a minimum depth of 7.7 m, substantially shallower than the expected 16.7 m. Thus, MASW could not determine the actual foundation depth. Lateral resolution also depends on receiver spacing, and interpretation is complicated by the layered-earth assumptions used in processing and uncertainty about the velocities of soil–foundation mixtures.<br /><br />Overall, the findings demonstrate MASW’s potential for preliminary foundation characterization, especially when other information is unavailable. Further testing is needed to establish its vertical and lateral resolution and to develop reliable interpretation guidance. Two-dimensional surveys may help determine foundation geometry and surrounding-soil stiffness, supporting future estimates of load-carrying capacity.

Keywords

multichannel analysis of surface waves

MASW

bridge foundation

noninvasive geophysics

shear-wave velocity

surface-wave dispersion

subsurface stiffness

pile cap

foundation geometry

2D survey