Experimental Investigation on Shear Mechanical Behavior of Sandstone Containing a Pre-existing Flaw Under Unloading Normal Stress with Constant Shear Stress

2020 ◽  
Vol 53 (8) ◽  
pp. 3779-3792 ◽  
Author(s):  
Da Huang ◽  
Ying-Quan Guo ◽  
Duo-Feng Cen ◽  
Zhu Zhong ◽  
Yi-Xiang Song
Keyword(s):  
Experimental Investigation ◽  
Shear Stress ◽  
Mechanical Behavior ◽  
Normal Stress ◽  
Constant Shear ◽  
Constant Shear Stress

The influence of loading path on fault reactivation: a laboratory perspective

2020 ◽  
Author(s):  
Carolina Giorgetti ◽  
Marie Violay
Keyword(s):  
Shear Stress ◽  
Stress Field ◽  
Mechanical Behavior ◽  
Normal Stress ◽  
Principal Stress ◽  
Maximum Principal Stress ◽  
Fault Reactivation ◽  
Loading Path ◽  
Normal Faults ◽  
Loading Paths

<p>Despite natural faults are variably oriented to the Earth's surface and to the local stress field, the mechanics of fault reactivation and slip under variable loading paths (sensu Sibson, 1993) is still poorly understood. Nonetheless, different loading paths commonly occur in natural faults, from load-strengthening when the increase in shear stress is coupled with an increase in normal stress (e.g., reverse faults in absence of the fluid pressure increase) to load-weakening when the increase in shear stress is coupled with a decrease in normal stress (e.g., normal faults). According to the Mohr-Coulomb theory, the reactivation of pre-existing faults is only influenced by the fault orientation to the stress field, the fault friction, and the principal stresses magnitude. Therefore, the stress path the fault experienced is often neglected when evaluating the potential for reactivation. Yet, in natural faults characterized by thick, incohesive fault zone and highly fractured damage zone, the loading path could not be ruled out. Here we propose a laboratory approach aimed at reproducing the typical tectonic loading paths for reverse and normal faults. We performed triaxial saw-cut experiments, simulating the reactivation of well-oriented (i.e., 30° to the maximum principal stress) and misoriented (i.e., 50° to the maximum principal stress), normal and reverse gouge-bearing faults under dry and water-saturated conditions. We find that load-strengthening versus load-weakening path results in clearly different hydro-mechanical behavior. Particularly, prior to reactivation, reverse faults undergo <em>compaction</em> even at differential stresses well below the value required for reactivation. Contrarily, normal faults experience <em>dilation</em>, most of which occurs only near the differential stress values required for reactivation. Moreover, when reactivating at comparable normal stress, normal faults (load-weakening path) are more prone to slip seismically than reverse fault (load-strengthening path). Indeed, the higher mean stress that normal fault experienced before reactivation compacts more efficiently the gouge layer, thus increasing the fault stiffness and favoring seismic slip. This contrasting fault zone compaction and dilation prior to reactivation may occur in different natural tectonic settings, affecting the fault hydro-mechanical behavior. Thus, to take into account the loading path the fault experienced is fundamental in evaluating both natural and induced fault reactivation and the related seismic risk assessment.</p>

Behaviour of recompacted residual soils in a constant shear stress path

2010 ◽  
Vol 47 (6) ◽  
pp. 648-661 ◽  
Author(s):  
S. M. Junaideen ◽  
L. G. Tham ◽  
K. T. Law ◽  
F. C. Dai ◽  
C. F. Lee
Keyword(s):  
Shear Stress ◽  
Soil Mechanics ◽  
Stress Path ◽  
Experimental Program ◽  
Published Data ◽  
Residual Soils ◽  
Constant Shear ◽  
Constant Shear Stress ◽  
Path Dependent ◽  
Soil Behaviour

The significance of studying soil behaviour in a constant shear stress path to understand rain-induced slope failures and debris flows has long been recognized. Studies with constant shear tests have, however, been limited, and some past results from undisturbed soils appear to show stress path–dependent volume change behaviour. The present study systematically investigates the behaviour of recompacted residual soils in a constant shear stress path using a comprehensive experimental program. It is shown that the results of this test program and previously published data can be interpreted using the concepts of critical-state soil mechanics.

scholarly journals Yielding Characteristic and Non-Coaxiality of Toyoura Sand on p′-Constant Shear Stress Plane

2011 ◽  
Vol 51 (1) ◽  
pp. 179-190 ◽  
Author(s):  
Hiroshi Ohkawa ◽  
Jiro Kuwano ◽  
Takafumi Nakada ◽  
Shinya Tachibana
Keyword(s):  
Shear Stress ◽  
Constant Shear ◽  
Stress Plane ◽  
Constant Shear Stress ◽  
Toyoura Sand

scholarly journals Aging, Rejuvenation and Thixotropy in Complex Fluids: Time-dependence of the Viscosity at Rest and under Constant Shear Rate or Shear Stress

2008 ◽  
Vol 18 (5) ◽  
pp. 53298-1-53298-13
Author(s):  
Daniel Quemada
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Volume Fraction ◽  
Complex Fluids ◽  
Transient Behaviour ◽  
Volume Fractions ◽  
Constant Shear ◽  
Constant Shear Stress ◽  
Constant Shear Rate ◽  
Viscosity Changes

Abstract Complex fluids exhibit time-dependent changes in viscosity that have been ascribed to both thixotropy and aging. However, there is no consensus for which phenomenon is the origin of which changes. A novel thixotropic model is defined that incorporates aging. Conditions under which viscosity changes are due to thixotropy and aging are unambiguously defined. Viscosity changes in a complex fluid during a period of rest after destructuring exhibit a bifurcation at a critical volume fraction ϕc2. For volume fractions less than ϕc2 the viscosity remains finite in the limit t →∞. For volume fractions above critical the viscosity grows without limit, so aging occurs at rest. At constant shear rate there is no bifurcation, whereas under constant shear stress the model predicts a new bifurcation in the viscosity at a critical stress σB, identical to the yield stress σy observed under steady conditions. The divergence of the viscosity for σ≤σB is best defined as aging. However, for σ > σB, where the viscosity remains finite, it seems preferable to use the concepts of restructuring and destructuring, rather than aging and rejuvenation. Nevertheless, when a stress σA(≤σB) is applied during aging, slower aging is predicted and discussed as true rejuvenation. Plastic behaviour is predicted under steady conditions when σ > σB. The Herschel-Bulkley model fits the flow curve for stresses close to σB, whereas the Bingham model gives a better fit for σ >> σB. Finally, the model’s predictions are shown to be consistent with experimental data from the literature for the transient behaviour of laponite gels.

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