Dynamic properties of sand from dry to fully saturated states

Abstract

By using bender and extender elements test, the velocities of the primary and shear waves, V p and V s respectively, were measured for a sandy material by gradually varying the degree of saturation, S r , between the dry and fully saturated states. The effect on the results of varying the relative density and effective confining pressure was also studied. The measurements clearly reveal that for a certain optimum S r , which is around 0 . 7-0 . 9% for the chosen sand, the value of the shear modulus G reaches a maximum value, whereas the corresponding Poisson's ratio í attains a minimum value. The values of the shear modulus corresponding to S r % 0% and S r 100% tend towards the same value. For values of Skempton's B parameter greater than 0 . 99, the values of V p and í rise very sharply to those of water. The predictions from Biot's theory with respect to the variation of V p with S r match well with the measured experimental data.En utilisant des essais sur des éléments de cambrage et d'extension, on a mesuré les vitesses V p et V s , des ondes primaires et de cisaillement respectivement pour une matière sableuse, en faisant varier progressivement le degré de saturation (S r ) entre les états sec et entièrement saturé. On a également examiné l'effet de la variation de la densité relative et de la contrainte de confinement utile sur les résultats. Ces mesures révèlent clairement que pour un S r optimum, relevé aux alentours de 0,7 à 0,9% pour le sable choisi, le module de cisaillement (G) atteint une valeur maximale, tandis que le ratio de Poisson (í) atteint une valeur minimale. Les valeurs du module de cisaillement correspondant à S r % 0% et S r 100% présentent une tendance vers la même valeur. Pour des valeurs du paramètre B de Skempton supérieures à 0,99, les valeurs V p et í augmentent considérablement par rapport à celles de l'eau. Les prédictions de la théorie de Biot relativement à la variation de V p en fonction de S r correspondent parfaitement aux données relevées expérimentalement.

Damping of Sands for Varying Saturation

“…For the medium and coarse sands, the minimum value of D o has been found to be associated with the smallest S r value (the near dry state) that can be achieved experimentally. It should be noted that the present observations related to the effect of saturation on the damping ratio are similar to those reported by Cho and Santamarina (2001) and Kumar and Madhusudhan (2011) with respect to the effect of the variation of S r on the shear modulus of sands. At the optimum degree of saturation, the magnitude of the shear modulus becomes the maximum (Madhusudhan 2011).…”

“…Five different relative densities (D r ), namely, 40, 50, 60, 70, and 80% were used for performing the damping tests. The necessary calibration exercise was first performed for the dry state of the material to find the required height of fall for a given relative density (Kumar and Madhusudhan 2011). The samples associated with a given relative density were prepared in five different layers.…”

“…The thickness of the each layer was kept the same. To prepare a sample with a given degree of saturation, the procedure described in Kumar and Madhusudhan (2011) was followed. For the sake of completeness, this procedure is described herein.…”

“…From a known value of B, the value of S r is then indirectly determined from the basic definition of the parameter B (Kumar and Madhusudhan 2011). The magnitude of B was kept greater than 0.99.…”

“…From the available literature, it is understood that for granular materials, especially for silts and fine sands, a certain optimum degree of saturation exists, corresponding to the maximum shear modulus (Cho and Santamarina 2001;Kumar and Madhusudhan 2011). This optimum degree of saturation has been found to increase with a decrease in the grain size of granular material (Cho and Santamarina 2001).…”