Modified Fixed Wall Oedometer When Considering Stress Dependence of Elastic Wave Velocities

Abstract

A modified oedometer cell for measuring the applied stresses and elastic waves at the top and bottom of the specimen is developed to evaluate the effect of the side friction on the stress dependence of the elastic wave velocities. In the modified cell, two load cells are installed at the top and bottom plates, respectively. To generate and detect the compressional and shear waves, a pair of piezo disk elements and a pair of bender elements are mounted at both the top and bottom plates. Experimental results show that the stresses measured at the bottom are smaller than those measured at the top during the loading and vice versa during unloading, regardless of the densities and heights of the specimens. Under nearly saturated conditions, the compressional wave velocities remain almost constant for the entire stress state. With plotting stresses measured at top, the shear wave velocities during unloading are greater than those during loading, whereas with plotting stresses measured at bottom, the shear wave velocities during unloading are smaller than those during loading owing to the side friction. The vertical effective stress may be simply determined from the average values of the stresses measured at the top and bottom of the specimens.

Modern Displacement Measuring Systems Used in Geotechnical Laboratories: Advantages and Disadvantages

“…The fact is that the bender elements can be mounted in any geotechnical device capable of controlling stresses while measuring deformations, or vice versa, as mentioned by Ferreira [ 42 ]. Such equipment includes: odometer [ 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 ], direct shear apparatus [ 65 , 73 ], resonant-column [ 74 , 75 , 76 , 77 ], centrifuge [ 78 , 79 ], hollow cylinder [ 80 , 81 , 82 ], calibration chambers [ 83 , 84 ], true triaxial and cubical cel apparatus [ 85 , 86 ]. Some examples are presented in Section 6 .…”

“…Another interesting solution was proposed by Lee et al [ 71 ] from Korea universities, who evaluated the effect of side friction (in conditions of full or incomplete sample saturation) on the stress dependence of the elastic wave velocities on the top and bottom of the silica sand sample in an odometer. For this purpose, they were modified an odometer cell by installing a pair of piezo disk elements and a pair of bender elements at both top and bottom plates ( Figure 17 ).…”

“…TL and BL denote the load cells installed at the top and bottom plates, respectively. In addition, BE and PDE denote the bender elements and piezo-disk elements (after [ 71 ], in accordance with 2021 Creative Common CC BY License of MDPI).…”

Use of a Piezoelectric Bender Element for the Determination of Initial and Final Setting Times of Metakaolin Geopolymer Pastes, with Applications to Laterite Soils

“…The bender element test is considered to be one of the outstanding non-destructive tests for numerous reasons, such as its capacity for real-time monitoring [ 1 ]. In combination with piezoelectric sensors, the bender element can effectively determine the shear wave velocity and the initial shear modulus of materials in studies [ 2 , 3 , 4 , 5 , 6 ]. As an example, the bender element test was applied to studying soil characteristics, e.g., thawing and stress restoration in artificial frozen sandy soils [ 7 ], transition evaluation of fine sand from capillarity to cementation [ 8 ], expansion-induced crack propagation monitoring in rocks [ 9 ], response monitoring of transitional mixtures retaining the memory of in-situ overburden pressure [ 10 ], etc.…”

Piezoelectric Ring Bender for Characterization of Shear Waves in Compacted Sandy Soils

“…Youn et al [ 9 ] incorporated BEs into resonant column and torsional shear testing equipment, and they compared the values of the shear wave velocities obtained from the resonant column test, torsional shear test, and BEs. Lee et al [ 31 , 32 ] suggested a new oedometer cell with BEs to evaluate both the compressibility of soils and the shear wave velocities under the zero-lateral strain condition. Byun et al [ 33 , 34 ] showed that the BE could be used to monitor the stiffness characteristic of soils during direct shear tests.…”