Using geophysical data to quantify stress transmission in gap-graded granular materials

Abstract

The behaviour of gap-graded granular materials, i.e. mixtures of coarse and cohesionless finer grains having a measurable difference in particle size, does not always confirm to established frameworks of sand behaviour.Prior research has revealed that the role of the finer particles on the stress-strain response, liquefaction resistance, and internal stability of non-cohesive gap-graded soils is significant and complex, and highly dependent on both the volumetric proportion of finer particles in the material and the coarse-particle to finer-particle size ratio.Quantifying the participation of the finer particles on the stress transmission and overall behaviour is central to understanding the behaviour of these materials. However, no experimental technique that can directly quantify the contribution of finer particles to the overall behaviour has hitherto been proposed. This paper explores to what extent the participation of finer particles can be assessed using laboratory geophysics, recognizing that granular materials act as a filter to remove the high frequency components of applied seismic / sound waves.Discrete element method simulations are performed to understand the link between particle-scale stress transmission and the overall response observed during shear wave propagation. When the proportion of finer particles is increased systematically both the shear wave velocity (VS) and low-pass frequency (flp) increase sharply once a significant amount of the applied stress is transferred via the finer particles. This trend is also observed in equivalent laboratory experiments. Consequently, the flp-VS relationship can provide useful insights to assess whether the finer particles contribute to stress transmission and hence the mechanical behaviour of the gap-graded materials. 3 List of symbols and notation b measure of the portion of the finer particles that contribute to the active intergrain contacts as proposed by Thevanayagam et al. (2002) CN number contacts per particle (particle coordination number) 𝐶 ! """" mean coordination number

Using Ultrasonic Reflection Resonance to Probe Stress Wave Velocity in Assemblies of Spherical Particles

“…7-i, where it can be discrete regime continuous regime roughly seen that higher proportion of "discrete regime" glass ballotini may introduce larger measurement errors of the ultrasonic reflection method. The behavior of gap-graded granular materials (i.e., mixtures of coarse and cohesionless fine grains) is however highly complex, and depends upon i) the ratio of the large and small diameters and ii) volumetric proportion of the finer fraction [35], therefore further comprehensive investigation is required for the application of the ultrasonic reflection method in this scenario. The main parameters of the tested glass ballotini, as well as layer 1 of hard PVC and layer 2 of steel, are listed in Table II.…”

“…Overall, to deal with large soil particles, both the timeof-flight and the reflection resonance methods need to adopt lower frequency sensors. The ratio of the wavelength to particle size seems to be the dominant factor for the applicability of the ultrasonic reflection method, while the reliability of the timeof-flight method can be additionally affected by soil thickness, soil stress and so on, as indicated in [1], [35]. Future work will investigate the robustness of the reflection resonance method through in-situ practice.…”

Acoustic Emission Enabled Particle Size Estimation via Low Stress-Varied Axial Interface Shearing

“…10-a) shows that the presence of different sizes of glass ballotini attenuates the AE signal intensity as compared to the AE response to the single size specimens, so that these two linear models do not collapse into the same curve. This attenuation could also be determined by i) the diameter ratio of the coarse and fine particles and ii) volumetric proportion between them [37]. Despite these complexities, the AE counts at 20mV threshold voltage can present two linear models that are relatively close to each other, as seen in Fig.…”

“…To further assess the correlation between the AE signal and the particle size, a group of mixed sizes of glass ballotini specimens (known as "gap-graded granular materials" [37]) are tested by following the same experimental procedures in Fig. 3, including 25% 3 mm + 75% 1 mm, 50% 3 mm + 50% 1mm, 75% 3 mm + 25% 1 mm, 25% 5 mm + 75% 1 mm, 50% 5 mm + 50% 1 mm, and 75% 5 mm + 25% 1 mm (all percentages refer to the volumetric proportions).…”

Linking inherent anisotropy with liquefaction phenomena of granular materials by means of DEM analysis

“…where N p is the total number of particles; CNi is the coordination number per particle. Following Otsubo et al (2022), the mechanical void ratio (e à ) was calculated by counting the volume of non-active particles as the void volume. The CN à 0 and e à 0 values are listed in Tables 1 and 2.…”