Stress relaxation behavior in Virginia Beach sand

Abstract

Effects of strain rate on the stress-strain and subsequent stress relaxation behaviors have been studied by performing triaxial compression tests on dense Virginia Beach sand specimens at three different strain rates (ratio of 256 between the slowest and the fastest) under low and high confining pressures. For the tests performed under low confining pressure, the specimens that were initially sheared at a faster rate showed a slightly higher amount of stress relaxation, but almost identical stress-strain behaviors were achieved. For tests performed under high confining pressure, the same amount of strength was achieved at high axial strains (10% to 20%) but specimens sheared at higher strain rates showed a slightly stiffer stress-strain response at low axial strains (up to 10%). Similar to the tests performed under low confining pressure, higher strain rates produced to some extent higher amounts of stress relaxation.Effects of correction of axial strain due to load cell expansion and drainage condition during stress relaxation have also been studied and the results indicated that correction of axial strain and undrained condition will both increase the observed amount of stress relaxation.Moreover, a 1-day stress relaxation curve was obtained by connecting the ending stress-strain points of six stress relaxation tests initiated at different deviator stress levels, and this curve was found to be different from the 1-day creep curve obtained from a previous study. A long-term stress relaxation test was also performed, and it showed linear reduction of deviator stress with the logarithm of time during stress relaxation. Observations made are all aligned with the phenomenon of static fatigue and the proposed mechanism for time effects in granular materials.

Time-dependent behaviour of sand with different fine contents under oedometric loading

“…They were performed under cylindrical stress conditions in a drained triaxial setup and the zero strain rate condition was only applied for the axial strain component ( 1 ϭ 0, 3 ≠ 0, 1 ≠ 0, 3 ϭ 0, where 1 is the major principal strain rate, 3 is the minor principal strain rate, 1 is the major principal effective stress rate, and 3 is the minor principal effective stress rate). A comparison of drained to undrained ( 1 ϭ 0, 3 ϭ 0, 1 ≠ 0, 3 ≠ 0) triaxial relaxation tests by Lade and Karimpour (2014) showed very similar relaxation of the deviator stress q. The drained tests showed contractive behaviour while the undrained tests were in some cases dilative leading to negative pore water pressures.…”

“…Experimental findings show that the relaxation behaviour of granular and fine-grained soils are qualitatively different. The relaxation effect in coarse-grained soils is much larger than the viscous effects rising from creep or a stepwise change in the strain rate (Pham Van Bang et al 2007;Lade 2009;Lade et al 2009;Lade and Karimpour 2014). This cannot be described in the framework of the isotache concept.…”

Silt türü bir Zeminin Gerilme Rahatlaması üzerine Deneysel bir Çalışma

“…Tane boyutu, tane şekli, su içeriği, ikinci ve üçüncü eksenlerden çevresel basınç gibi çeşitli parametrelerin gerilme rahatlaması süresi ve oranı üzerinde etkili olduğu ilgili çalışmalar ile belirlenmiştir (Sanchez-Giron et al, 2001;Lade and Karimpour, 2015;Kutergin et al, 2013;Levin et al, 2019). Gerilme rahatlaması zamana bağlı plastik deformasyonun başlaması sonucu oluşmaktadır.…”