Frictional strength of ground dolerite gouge at a wide range of slip rates

Abstract

We conducted a series of rotary‐shear friction experiments on ground dolerite gouges, in which the amount of adsorbed moisture increases with grinding time (tgr), at room temperature and humidity, a normal stress of 2 MPa, and constant equivalent slip rates (Veqs) ranging from 20 µm/s to 1.3 m/s. Their frictional strength changed with Veq and tgr in three different ways depending on Veq and the gouge temperature (T). At Veq ≤ 1.3 cm/s, T did not exceed 80°C, and the steady state friction coefficient (μss) ranged from 0.59 to 0.80. μss changes little with Veq, while μss at a given Veq systematically increases with tgr probably due to moisture‐adsorbed strengthening of gouges. At Veq = 4 cm/s, T exceeded 100°C, and dehydration of gouges resulted in roughly the same μss values (0.60–0.66) among gouges with different periods of tgr. At Veq ≥ 13 cm/s, T reached 160–500°C, and μss dramatically decreases with Veq to 0.08–0.26 at Veq = 1.3 m/s, while μss at a given Veq systematically decreases with tgr. At these fast Veqs, dehydration of gouges likely occurred too fast for water vapor to completely escape out from the gouge layer. Therefore, faster dehydration at faster Veq possibly resulted in a larger pore pressure increase and lower frictional strength. In addition, because gouges with longer periods of tgr contain larger amounts of adsorbed moisture, they became weaker due to larger increases in pore pressure and hence larger amounts of reduction in frictional strength.

Velocity‐dependent frictional weakening of large rock avalanche basal facies: Implications for rock avalanche hypermobility?

“…Rock avalanches usually have extremely longer runouts than the slip displacements used in the experimental study. Therefore, referred to the studies of deformed fault gouges and fine landslide gouges conducted by others [ Kitajima et al ., ; Ferri et al , ; Sawai et al ., ; Togo and Shimamoto , ; French et al ., ; Yang et al ., ; De Paola et al ., ; Wada et al ., ], we assume that μ can be extrapolated to natural rock avalanches using the empirical equation proposed based on the experimental data.…”

“…Besides the assumptions for the distributions of the shearing velocity and stress over the shearing surface, the biggest error source for the accuracy of soil friction is the existence of the friction associated with the Teflon sleeve and upper host rock. As far as possible to eliminate this error, one effective way reported in literatures [ Mizoguchi et al ., ; Kitajima et al ., ; Sawai et al ., ; Rempe et al ., ; Wada et al ., ] was used in the adjustment of the experimental data. That is, several runs should be firstly performed without applying any normal stress to determine the friction between the Teflon sleeve and upper host rock.…”

Normal Stress‐Dependent Frictional Weakening of Large Rock Avalanche Basal Facies: Implications for the Rock Avalanche Volume Effect

“…Wang et al () proposed that the marked frictional weakening of soil collected from the Yigong rock avalanche basal facies was caused by the coupled effects of thermal pressurization and thermal moisture fluidization induced by frictional heating. In the literature, the dynamic frictional weakening of gouges or fault rocks has been explained via various hypotheses related to temperature rise, such as frictional melting (Hirose & Shimamoto, ), flash heating (Beeler et al, ; Goldsby & Tullis, , ; Kohli et al, ; Rice, ; Yuan & Prakash, ), thermal decomposition (Han et al, ), and thermal pressurization (Brantut et al, ; Hirono et al, ; Wada et al, ). Flash heating is a process where highly stressed fault surface asperities are thermally weakened by local frictional heating during rapid slip (Beeler et al, ; Kohli et al, ; Rice, ).…”

“…Thermal pressurization points to the generation of excess pore pressure of fluid (particularly water) within gouges induced by frictional heating, which can result in reduced frictional strength by decreasing effective normal stress (Hirono et al, ; Noda & Shimamoto, ; Rice, ; Veveakis et al, ). In this hypothesis, water vaporization, which is commonly observed in the rotary shear tests of water‐containing samples with rapid slips, is proposed as a source of thermal pressurization (Brantut et al, ; Chen, Niemeijer, Yao, & Ma, ; Wada et al, ; Wang et al, ). Using a moisture sensor, Brantut et al () monitored the generation of water vapor caused by frictional heating during rapid shearing in clay‐bearing gouge samples.…”

“…Moreover, water vaporization was commonly observed in previous rotary shear tests in samples deformed at V eq ≥ 0.61 m/s (Wang et al, ). Coseismic experimental studies of fault gouges have also reported water vaporization, which is expected to be an important mechanism for fault frictional weakening, especially in shallow faults (Brantut et al, ; Boutareaud et al, ; Chen, Niemeijer, Yao, & Ma, , Chen, Niemeijer, & Fokker, ; Kitajima et al, , ; Wada et al, ).…”