New Approach to Concurrent V-s and V-p Measurements Using Bender Elements

• Type: Article in International Scientific Journal
• Date: 2021-05-06

Authors

António Viana da Fonseca (Author) FEUP; Cristiana Ferreira (Author) FEUP; Fredy Alonso Diaz Duran (Author) Other; Giovanni Cascante (Author) Other

Journal

Title: Geotechnical Testing Journal

Vol. 44 No. 6

Pages: 1801-1820

ISSN: 0149-6115

Publisher: American Society for Testing and Materials

Indexing

ISI Web of Knowledge - 3 Citations

ISI Web of Science

Scopus - 3 Citations

Scientific classification

CORDIS: Technological sciences > Engineering > Civil engineering > Geotechnics

FOS: Engineering and technology > Civil engineering

Other information

Authenticus ID: P-00V-K8G

DOI: 10.1520/gtj20200207

Abstract (EN): Bender elements (BEs) have become a routine geotechnical laboratory tool for seismic wave velocity measurements. Since the 1980s, this testing technique has gained popularity, currently being available in many geotechnical laboratories worldwide in a variety of apparatuses. The advantage of simultaneously measuring small- and large-strain soil stiffnesses in each device and the easiness and low-cost implementation of BE are the main reasons for their common application. Although there is already a standardized procedure for BE testing (ASTM D8295-19, Standard Test Method for Determination of Shear Wave Velocity and Initial Shear Modulus in Soil Specimens Using Bender Elements), the use of high-frequency pulses for the simultaneous measurement of compressional (V-p) and shear (V-s) wave velocities is not considered. In contrast, the use of high-excitation frequencies is usually discouraged, as they tend to induce spurious participation of high-vibration modes in the BE response. However, this work shows that the use of higher vibration modes can be advantageous to evaluate P-wave velocities from standard BE testing. Thus, this paper presents a new approach for the concurrent measurements of V-p and V-s using a typical installation of BE. The new approach is first demonstrated by experimental measurements and subsequently validated using high-frequency laser vibrometer measurements of the actual BE deformation (nanometer scale) under different excitation frequencies. The laser vibrometer measurements show the displacements of the transmitter BE as a function of the input frequency in not only the horizontal but also in the vertical directions, demonstrating the generation of P-waves when higher vibration modes are excited. The measured V-p values are shown to be in good agreement with the predicted values using Biot's equations. Thus, the proposed methodology addresses the current knowledge gap in the use of BE for concurrent P-wave and S-wave velocity measurements. The generated wavelengths are large enough to travel through the soil skeleton instead of the pore water only.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 20