Bender elements in stiff cemented clay: shear wave velocity (V_s) correction by applying wavelength considerations

Abstract

For the quality control of cement mixing in clays, small-strain shear stiffness Gmax is now increasingly being used due to enhanced repeatability in shear wave velocity (Vs) measurements. These stiff cemented clays have higher resonant frequencies that require the use of higher input frequencies in bender element testing for reliable Vs measurements. However, the practical requirements for suitable signals (with minimal near-field effects and wave reflections) can often be difficult to implement. To facilitate such Vs measurements, the current study proposes a methodology that can correct Vs values corresponding to lower wave propagation distance to wavelength ratios (Ltt/λ) to more reliable values of Vs at reference Ltt/λ criterion suggested in previous studies (e.g., 2, 3.33, and 4). Two clay types are mixed with ordinary Portland cement and various mix ratios are utilized to cover a wider range of soil stiffnesses. Based on the collected database, it is found that the resulting fitting functions enable the reasonable estimation of the stabilized Vs values corresponding to the suggested Ltt/λ criterion regardless of the nature of the input sine signal.

Shear Wave Velocity Measurements in Tropical Peat Using In-house Device

“…Hence, it was anticipated from the beginning that results measured can be very much different from the theoretical data mentioned in Table (3). Table (8) and (9) shows the results of peat samples using the in-house BET device. A frequency of 500Hz was applied as the control variable for the proposed instrumentation setup.…”

“…Generally, two end caps each equipped with piezoelectric bender elements were used to generate and receive shear wave signals transmitted through the peat sample [7]. However, 𝑉 𝑠 travel across the sample will be subjected to various external disturbance including the near field effects that influence, P and S wave interference, and wave reflections which are challenges in performing BET [8].…”

Effect of fine particles on strength and stiffness of cement treated sand

“…In fact, the measured V s increases as L/λ ratio increases up to a certain extent, beyond which it remains almost constant. For soils, some studies have recommended to maintain a larger L/λ ratio [25][26][27]. In this study, the L/λ ratio for stiffer samples (i.e., 7% cement 28-day samples) are between 2.6 and 3 and for other samples it is greater than 3.3.…”

Review on the Test Methods and Devices for Mechanical Properties of Hydrate-Bearing Sediments

“…The bender elements are made of a transmitting bender element and a receiving bending element, and the sample is loaded by energized vibration (Figure 1). When a certain frequency of excitation signal voltage pulse is applied, the shear wave perpendicular to the vibration direction, which is generated by the transmitting bender element, is transmitted to the receiving bender element [36,37]. The entire shear-wave transmission time can be obtained by amplifying the signal with an external oscilloscope; the shear wave velocity can be calculated by adding the entire shear wave transmission time and sample length [38].…”