Determination of the Dynamic Soil Characteristics at the NGES

Abstract

Analysis of the field data collected at the National Geotechnical Experimentation Site (NGES) at Texas A&M University (TAMU) is outlined. Data have been collected along two measurement lines from two and multi-sensor arrays using a variety of sources. The data from each measurement line are processed separately. The STA/LTA procedure is applied in order to determine the P- waves arrival time. The P-wave velocity profile is determined by solving an inverse problem, where the difference between the theoretical arrival time, corresponding to a horizontally layered halfspace, with the experimental arrival time is minimized. The classical SASW method as well as the frequency- wavenumber analysis are used to determine the experimental dispersion curve. The dispersion curve is subsequently inverted to determine the S-wave velocity profile, using the a priori determined P-wave velocity profile. The width of peaks of the response in the frequency-wavenumber domain is used to determine the experimental attenuation curve. The attenuation curve is finally inverted to give the material damping ratio profile, while the already determined P- and S-wave velocity profiles are fixed in the inversion procedure. The determined soil profile is finally used to make a comparison between the theoretical and experimental frequency-wavenumber spectrum. The correspondence with experimental results is good. INTRODUCTION A data set collected at the National Geotechnical Experimentation Site (NGES) at Texas A&M University (TAMU) is made available to the community for interpretation. In this paper, the Seismic Refraction (SR) method, the classical Spectral Analysis of Surface Waves (SASW) method, and the Multi-channel Analysis of Surface Waves (MASW) method are used to determine dynamic soil properties. The SR method gives the P-wave arrival time from which the P-wave velocity profile of the soil is determined. The classical SASW method results in a composite dispersion curve and subsequently the S-wave velocity profile. The MASW method gives both the dispersion and attenuation curve. The material damping ratio profile is determined from the attenuation curve. Finally, the identified soil profiles are used to simulate the wave field recorded in the SASW test to verify the accuracy of the results. DETERMINATION OF THE P-WAVE VELOCITY Measurements were performed using two measurement lines A and B at the NGES. For each setup, waves were generated by means of sledgehammer impacts at the soil's surface. The response was recorded by means of a set of 62 receivers spaced at 0.61 m along a straight measurement line. The position of the source was