We have developed an application of 2D time-domain waveform tomography for detection of embedded sinkholes and anomalies. The measured seismic surface wavefields were inverted using a full-waveform inversion (FWI) technique, based on a finite-difference solution of 2D elastic wave equations and the Gauss-Newton inversion method.The key advantage of this approach is the ability to generate all possible wave propagation modes of seismic wavefields (body waves and Rayleigh waves) that are then compared with measured data to infer complex subsurface properties.The pressure-wave (P-wave) and shear-wave (S-wave) velocities are inverted independently and simultaneously. The FWI was applied to one synthetic and two real experimental data sets. The inversion results of synthetic data showed the useful capability of the waveform analysis in identifying an embedded void. The inversion results of real data sets showed that the waveform analysis was able to delineate (1) an embedded concrete culvert and (2) a complex profile with an embedded void and highly variable bedrock laterally and vertically. An independent invasive test (standard penetration test) was also conducted to verify the seismic test results.

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Currently (2007Currently ( -2010, AASHTO's LRFD design of deep foundations recommends resistance factors for a variety of scenarios (e.g., method of analysis, number of load tests, etc.). Generally, values account for a desired level of reliability and are based on comprehensive databases (not site specific) of predicted versus measured resistances. Unfortunately, no consideration is given to locations of boreholes with respect to foundation elements, to spatial variability of design properties over the site or the use of load testing on LRFD assessment. The present work considers the case of side friction on axially loaded drilled shafts as assessed from laboratory analysis of rock core samples. Geo-statistical principles are used to rationally account for (1) the presence and amount of site specific load testing with borehole data in the footprint, (2) the availability of off-site load test data, (3) the amount of site specific borehole sampling, and (4) the presence or not of borehole data at production shaft locations. In agreement with previous studies, spatial variability within a site is identified as a dominating contributor to overall prediction uncertainty. Additionally, it is shown that spatial variability may only be eliminated by using borings inside shaft footprints and not through additional load testing or collection of borehole data at other locations on a site. A case study with field data is used to illustrate the approach for practice in Florida limestone.

An application of two-dimensional time-domain waveform tomography to map the extent of open chimneys at a variable karstic limestone site is presented. The seismic surface wave fields were measured next to three open chimneys and inverted with a full-waveform inversion technique, which was based on a finite-difference solution of two-dimensional elastic wave equations and the Gauss–Newton inversion method. Both the compression wave (P-wave) and shear wave (S-wave) velocities were inverted independently and simultaneously to increase the credibility of the characterized profiles. The waveform analysis successfully profiled embedded low-velocity zones and highly laterally and vertically variable limestone. The inverted results are consistent with the known open chimneys observed from the ground surface. The Poisson's ratio determined from the inverted P-wave and S-wave velocities is consistent with soil types: high values of 0.3 to 0.5 for silt and clay and low values of 0.1 to 0.2 for limestone. Results show that the full-waveform inversion technique is applicable to both shallow and deep foundation design in which soil stratigraphy and variability are important. The technique is also computationally practical, because the results were all achieved in about 3 h of computer time on a standard laptop computer.

The paper presents an application of 2-D time-domain waveform tomography for detection of embedded voids/anomalies. The measured seismic surface wave fields were inverted using a full waveform inversion (FWI) technique, based on a finite-difference solution of 2-D elastic wave equations and Gauss-Newton inversion method. The key advantage of this approach is the ability to generate all possible wave propagation modes of seismic wavefields (body waves and Rayleigh waves) that are then compared with measured data to infer complex subsurface properties. Both the pressure wave (P-wave) and shear wave (S-wave) velocities are inverted independently and simultaneously for possible indication of soil types. The inversion results of real data set show that the waveform analysis was able to delineate a complex profile with an embedded void and highly variable bedrock both laterally and vertically. Independent invasive test (standard penetration test, SPT) was also conducted to verify the seismic test results.