Idealized Sine Wave Approach to Determine Arrival Times of Shear Wave Signals Using Bender Elements

TY - JOUR

T1 - Idealized Sine Wave Approach to Determine Arrival Times of Shear Wave Signals Using Bender Elements

AU - Khan, Qasim

AU - Moon, Sung-Woo

AU - Ku, Taeseo

PY - 2020/1

Y1 - 2020/1

N2 - Determining small strain stiffness Gmax of soils in laboratory is generally achieved using bender elements. Shear wave propagation is affected by the soil medium and boundary conditions causing distortion in output signals, which introduces error in travel time estimates. This study proposes a novel technique for determining first arrival time in a systematic manner. Based on idealized sine waves, this technique modifies peak-to-peak results to find arrival times using the output frequency of received signal. By incorporating the initial half wavelength of received signals, five methods depending on the length of signal chosen for calculating the output frequency are proposed in this paper. The applicability of the proposed technique is evaluated based on signals reported in published literature and signals obtained for Singapore marine clay (uncemented and lightly cemented). For most soil types and testing conditions, it was demonstrated that the proposed technique produces close estimates with reported original arrival times. On the contrary, other techniques such as the peak-to-peak, cross-correlation, and cross spectrum often underestimated shear wave velocities when the output signals contains relatively low frequency contents. Consequently, the proposed technique significantly reduces subjectivity and produces improved reliability in estimating specific arrival times without the need of any frequency sweep. Moreover, by incorporating the quality and shape of signals into the analysis, better estimates of first arrival can be established especially for noisy signals or signals affected by near-field effects.

AB - Determining small strain stiffness Gmax of soils in laboratory is generally achieved using bender elements. Shear wave propagation is affected by the soil medium and boundary conditions causing distortion in output signals, which introduces error in travel time estimates. This study proposes a novel technique for determining first arrival time in a systematic manner. Based on idealized sine waves, this technique modifies peak-to-peak results to find arrival times using the output frequency of received signal. By incorporating the initial half wavelength of received signals, five methods depending on the length of signal chosen for calculating the output frequency are proposed in this paper. The applicability of the proposed technique is evaluated based on signals reported in published literature and signals obtained for Singapore marine clay (uncemented and lightly cemented). For most soil types and testing conditions, it was demonstrated that the proposed technique produces close estimates with reported original arrival times. On the contrary, other techniques such as the peak-to-peak, cross-correlation, and cross spectrum often underestimated shear wave velocities when the output signals contains relatively low frequency contents. Consequently, the proposed technique significantly reduces subjectivity and produces improved reliability in estimating specific arrival times without the need of any frequency sweep. Moreover, by incorporating the quality and shape of signals into the analysis, better estimates of first arrival can be established especially for noisy signals or signals affected by near-field effects.

KW - Bender Elements

KW - Shear Waves

KW - First Arrival

KW - Peak-to-Peak

KW - Output Frequency

U2 - 10.1520/GTJ20170121

DO - 10.1520/GTJ20170121

M3 - Article

VL - 43

JO - Geotechnical Testing Journal

JF - Geotechnical Testing Journal

SN - 0149-6115

IS - 1

M1 - 20170121

ER -