Effect of pore pressure buildup on slowness of rupture propagation

Abstract

Pore fluid pressure is known to play an important role in brittle fracture initiation and propagation, yet the underlying mechanisms remain unclear. We conducted triaxial experiments on saturated porous sandstones to investigate effects of pore pressure buildup on the slowness of shear rupture propagation at different confining pressures. At low to intermediate confinements, rocks fail by brittle faulting, and pore pressure buildup causes a reduction in rock's shear strength but does not induce measurable differences in slip behavior. When the confinement is high enough to prohibit dynamic faulting, rocks fail in the brittle‐ductile transitional regime. In the transitional regime, pore pressure buildup promotes slip instability on an otherwise stably sliding fracture. Compared to those observed in the brittle regime, the slip rate, stress drop, and energy dissipated during rupture propagation with concurrent pore pressure buildup in the transitional regime are distinctively different. When decreasing confining pressure instead, the slip behavior resembles the ones of the brittle regime, emphasizing how the observed slowness is related to excess pore pressure beyond the effective pressure phenomenon. Analysis of the mechanical data using existing theoretical models confirms these observations. Quantitative microstructural analyses reveal that increasing pore pressure lessens the dilatancy hardening during failure, thus enhances slip along the localized zone in the transitional regime. Our experimental results suggest that pore pressure buildup induces slow slip in the transitional regime, and slip rates along a shear fracture may vary considerably depending on effective stress states.

Experimental study on strain behavior and permeability evolution of sandstone under constant amplitude cyclic loading‐unloading

“…22 Inspired by the integral path independent of J integral, 23 the shear fracture energy of sandstone before the peak stress was as follows 22 Inspired by the integral path independent of J integral, 23 the shear fracture energy of sandstone before the peak stress was as follows…”

Stabilizing Effect of High Pore Fluid Pressure on Slip Behaviors of Gouge‐bearing Faults

“…For instance, Sawai et al () demonstrate that decreasing effective pressure ( ) causes a transition from stable to unstable slip behavior in blueschist samples. Ougier‐Simonin and Zhu (, ) also observed that shear localization in porous rocks could become unstable by decreasing effective pressure as pore pressure increases during the post failure stage of faulting. In addition, French et al () and Scuderi et al () show that fluid pressurization can overcome velocity‐strengthening friction to result in accelerated fault slip.…”

The Influence of Fluid Filtration on the Strength of Porous Fluid-Saturated Brittle Materials

“…Увеличение объема порового пространства сопровождается резким падением локального порового давления. Известно, что неупругая деформация, как правило, носит локализованный характер и проявляется в виде узких полос локализованного сдвига (в геосредах такими макроскопическими полосами являются раз-ломные зоны) [8,15,19,36,39]. При этом прилегающие к полосам локализованного сдвига области материала или структурные блоки геосреды испытывают в основном упругую де-формацию.…”

“…В рамках данной концепции ключевая роль в процессах зарождения землетрясений в активных разломных зонах, слагаемых проницаемыми мате-риалами, принадлежит жидкости. Важную роль при этом играет не только поровое давле-ние жидкости, но и ее перераспределение в разломной зоне и прилегающих объемах ок-ружающих блоков [34][35][36]. Как отмечено в ряде работ, наличие жидкости оказывает су-щественное влияние на землетрясения, приуроченные к разломам, в связи с тем, что дав-ление жидкости частично компенсирует нормальное давление в плоскости разлома, сни-жая тем самым его сдвиговую прочность [34,37,38].…”