Measuring shear wave velocity of granular material using the piezoelectric ring-actuator technique (P-RAT)

Abstract

A precise evaluation of shear wave velocity, Vs, is a crucial issue in the design of foundations subjected to dynamic loading, liquefaction evaluation, and soil improvement control. Laboratory techniques such as resonant column (RC) and bender element (BE) have been developed over the years to measure Vs. At low strain (γ < 10−3), techniques based on piezoelectric elements (e.g., BE) can be considered superior to RC, as they can be used in conventional geotechnical devices (e.g., triaxial, oedometer, direct simple shear, etc.). However, it is a difficult task to verify that the obtained Vs values are correct and accurate, as there are several difficulties associated with these methods, including the mixed radiation of both primary and shear waves, near-field effects, boundary effects, and uncertain detection of first arrivals. This paper presents the use of a new technique to measure Vs in granular material, called the piezoelectric ring-actuator technique (P-RAT), developed at the Université de Sherbrooke. The paper also provides a detailed description of a unique interpretation method of the signals produced from this technique to minimize the difficulties associated with other techniques. The P-RAT has been incorporated into the well-known oedometer cell to measure the Vs of Péribonka sand through a series of oedometric tests, and the obtained results have been detailed, analyzed, and discussed in light of the basic state of knowledge of Vs and factors affecting it. Particular emphasis is also placed on the validation of the accuracy of the P-RAT by means of reliable experimental measurements available in literature.

Stiffness– and damping–strain curves of sensitive Champlain clays through experimental and analytical approaches

“…This apparatus offers the ability of measuring the soil stiffness over a wide range of strain spectrum from 0.001% to 10%, thus reduce the difficulties and the sources of uncertainty associated with other laboratory methods of constructing G/G 0 curves. The values of the small strain stiffness G 0 of the sensitive Champlain clays have been confirmed through another series of experimental tests using the piezoelectric ring-actuator technique (P-RAT) (Éthier 2009; Karray et al 2015). This paper, then, proposes a modification for the Sig4 model to take into account the pore water pressure built up with shear strain.…”

“…The piezoelectric ring-actuator technique (P-RAT) developed in the geotechnical laboratory at the Université de Sherbrooke (e.g., Éthier 2009; Karray et al 2015) has been utilized in this study to verify the small-strain T x SS results (i.e, G 0 ). The P-RAT has been incorporated into the conventional oedometer apparatus and the procedure is identical to that of the oedometer with the measurement of the soil shear wave velocity (V s ) to construct the relationship between the normalized shear wave velocity (V s1 ) of the soil and its void ratio (e).…”

“…For this particular reason, extensive research has been carried out by several researchers to study these characteristics of various soils at different sites, chiefly through laboratory tests on highly undisturbed samples regarded as representing intact conditions in the field. The bender element (BE) (e.g., Brignoli et al 1996;Yamashita et al 2009;Clayton 2011), and the piezo electric (e.g., Éthier 2009, Karray et al 2015) devices have been commonly utilized to evaluate low-strain dynamic soil properties. On the other hand, the resonant column (RC) is used to characterize the dynamic properties of soils from low to intermediate strain region, γ=0.0001% to 0.05% (e.g., Hardin 1970;Hardin and Drnevich 1972;Drnevich et al 1978;Tatsuoka et al 1978, Goudarzy et al 2017) and therefore the stiffness degradation and damping versus strain (G/G 0 -γ and ξ% -γ, where G 0 is the maximum shear stiffness of soils) curves are obtained from RC experiment up to intermediate strain level.…”

“…where ρ is the soil density) have their own difficulties such as the boundary and near field effects, the mixed radiation of both compression, P-and shear, S-waves, and the uncertain detection of first arrivals (Éthier 2009;Karray et al 2015). Bedding errors and system compliance as well as membrane penetration effects in the CTX generally limit its measurements to shear strains greater than 0.01% (e.g., Ishihara 1996).…”

Cyclic and dynamic behaviour of a Canadian sensitive clay

“…It is important to note the G0 (VS 2 ) was determined using the piezo-electric ring actuator technique (P-RAT) developed at Université de Sherbrooke. More details about the P-RAT technique are reported in [19].…”