Fig 2 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
a Picture of the HighSTEPS machine. b Details of the pressure vessel with high-pressure ports for pore fluid and confining oil, and uniaxial and coaxial feed throughs for electronics. c Jacketed sample with pore pressure lines connected to the pore pressure ports
Contexts in source publication
Context 1
... pressure vessel was built by RMP S.r.l., located in Rome, Italy. It is made in stainless steel, weighs about 500 kg, and has an external diameter of 700 mm and an internal diameter of 300 mm (Fig. 2b). It is designed to support 100 MPa confining pressure. The vessel holds up the vertical and horizontal pistons. To close the vessel, two doors of 130 kg each are equipped with 20 M36-size ...
Context 2
... to the other pore pressure intensifier, 2b, c and 4a) and one oil confining pressure line are connected to the pressure vessel. The pressure vessel is equipped with eight high-pressure co-axial feed throughs from Kemlon for acoustic sensors connection, 24 uniaxial feed throughs for strain gauge connection, and 3 type K thermocouple feed throughs (Fig. 2b and c). Another access port located at the bottom of the vessel is used to fill and empty the vessel with the confining oil. The confining medium is a silicon oil from Green Star High Tech lubricants. The oil tank is equipped with a pump which is used to fill the pressure vessel above (Fig. ...
Context 3
... connection, and 3 type K thermocouple feed throughs (Fig. 2b and c). Another access port located at the bottom of the vessel is used to fill and empty the vessel with the confining oil. The confining medium is a silicon oil from Green Star High Tech lubricants. The oil tank is equipped with a pump which is used to fill the pressure vessel above (Fig. ...
Context 4
... heating system, composed of two heating plates of 26 mm diameters with a high resistance, are fixed on the inner part of the vessel doors (Fig. 2b and c). The maximum temperature of 120 °C is limited by the confining oil flash point and the maximum temperature supported by the seals located on the vessel doors. Temperature is measured within the 2 heating plates and in the confining medium by 3 K-type thermocouples. Temperature is controlled by a closed-loop ...
Context 5
... vertical piston located in the upper part of the vessel is equipped with a compensation piston (co-axial and passive) in the lower part of the vessel, to avoid confining oil overpressure during fast vertical movements. The compensation piston is mechanically connected to the vertical piston thanks to 2 metallic clamps inside the pressure vessel (Fig. 2b, c). During shearing experiments, the vertical piston moves downward entering in the vessel and contemporaneously the compensation piston moves downward exiting the vessel, resulting in oil volume and oil pressure kept constant inside the vessel during the entire experiment. Moreover, the mechanical connection between the vertical piston ...
Context 6
... the vessel during the entire experiment. Moreover, the mechanical connection between the vertical piston and the compensation piston during the entire experiments ensures that the confining pressure does not contribute to the vertical load measured by the load cell. The sample assembly is located between the vertical and the compensation pistons (Fig. ...
Context 7
... a second time, we conducted a test where we sheared bare surfaces of gabbro (initial roughness applied with a P80-grit diamond abrasive disc) in single-direct shear configuration using the forcing blocks (Fig. 2c), the frictionless surface (Paragraph III B) and the jacketing system. The constant experimental conditions were: σ'n = 50 MPa, confining pressure, Pc = 30 MPa, pore pressure of 5 MPa, temperature 25 °C, sliding velocity 1*10 -2 m/s, and total displacement 1*10 -2 ...
Similar publications
For cable-stayed bridge, pylon and girder are one of the most important factors in the design process. Because of the length this structure, it needs to consider the type of the soil because different soil type can be resulting a different earthquake loads. In this study, the behavior of superstructure was investigated using time history analysis s...
Citations
... For the friction experiments, samples were first sawed as rectangular prisms of 70 × 35 × 13 mm and 20 × 35 × 13 mm, and rectified to a 80 ). Stainless steel sample holders were used in a single-direct shear setup, with a sample-to-sample interface on one side and a near-frictionless surface (GLYCODUR®, PTFE-based 3-layer material, having a friction <0.02) on the other side (Figs. ...
Water is ubiquitous within the pore space of rocks and has been shown to affect their physical and mechanical behaviour. Indeed, water can act on the rock strength via mechanical (i.e., reducing the effective stresses) or chemical effects (e.g., mineral dissolution, mineral alteration, subcritical crack growth, etc.). As rock macroscopic strength is controlled by both fracture toughness and friction at the grain-scale, these parameters should also be affected in presence of water. While some recent studies have measured the effect of water on both fracture toughness and frictional parameters to constrain the water weakening of porous rock compressive strength, the physical parameters, or rock characteristics, that influence this weakening are as of yet unclear. Here, we report a series of laboratory experiments in order to determine the influence of a water-saturated, as opposed to dry, environment on five limestones’ strengths. The uniaxial compressive strength, the mode-I fracture toughness and the static friction parameters are of interest. The experiments show that, for the tested limestones, water-saturated conditions provoke a reduction of the uniaxial compressive strength by up to 53 %. This reduction is accompanied by a reduction of the mode-I fracture toughness by up to 34 % and of the static friction by up to 16 %. Even though the water weakening of the uniaxial compressive strength is not influenced by the sample porosity, the mode-I fracture toughness reduction in the presence of water is accentuated for high-porosity limestones. Additionally, low porosity limestones appear to promote higher static friction reductions in water-saturated environments.
... This value is close to those obtained at room temperature in friction experiments on CM samples (μ peak = 0.6-0.8, see Carpenter et al., 2016;Violay et al., 2021) and on calcite gouge up to T = 600°C (μ peak = 0.4-0.7, see Verberne et al., 2015). ...
Little is known about the impact of pressure (P) and temperature (T) on faulting behavior and the transition to fault locking under high P–T conditions. Using a Paterson gas‐medium apparatus, triaxial compression experiments were conducted on Carrara marble (CM) samples containing a saw‐cut interface at ∼40° to the vertical axis at a constant axial strain rate of ∼1 × 10⁻⁵ s⁻¹, P = 30–150 MPa and T = 20–600°C. Depending on the P–T conditions, we observed the complete spectrum of deformation behavior, including macroscopic (shear) failure, stable sliding, unstable stick‐slip, and bulk deformation with locked faults. Macroscopic failure and stable sliding were limited to P < 100 MPa and T = 20°C. In contrast, at P ≥ 100 MPa or T ≥ 500°C, faults were locked, and samples with bulk deformation experienced strain hardening at strains ≤8.8%. At T = 100–400°C and P ≤ 100 MPa, we observed unstable stick‐slip behavior, where both fault reactivation stress and subsequent stress drop increased with increasing pressure and temperature, associated with increasing matrix deformation and less fault slip. Microstructures indicate a mixture of microcracking, twinning and dislocation activity (e.g., kinking and undulatory extinction) that depends on P–T conditions and peak stress. The transition from slip to lock‐up with increasing pressure and temperature is induced by an enhanced contribution of crystal plastic deformation. Our results show that fault reactivation and stability in CM are significantly influenced by P–T conditions, probably limiting the nucleation of earthquakes to a depth of a few kilometers in calcite‐dominated faults.
... In recent years, more and more rock works will be affected by high temperatures due to geological conditions and late environment, and the long-term stability of the rocks will be changed under the continuous loading (Violay et al. 2021;Zhang et al. 2022;Zhou et al. 2015). Temperature as an important factor affecting the mechanical properties of materials A. Jiang jiangannan@163.com ...
Deep underground civil works such as surrounding rocks of oil, gas pipelines and geothermal wellbore that pass through groundwater are often affected by the combined influences of thermal, hydraulic, and mechanical factors. In order to investigate the long-term stability of rock masses of this environment, creep experimental of quartz sandstone under the coupling effect of thermo-hydro-mechanical conditions. The study involved analyzing the long-term creep deformation, isochronous stress-strain curves, and long-term strength variations. Additionally, a fractional-order viscoelastic-plastic creep damage model was developed by integrating statistical damage analysis, Biot’s coefficient, and fractional-order integration theory. This model aimed to characterize the three-stage creep properties of different temperatures and water pressures. The experimental results indicate that the creep strain of quartz sandstone gradually increases with temperature and pore water pressure, while the long-term strength decreases. The axial creep strains of quartz sandstone are 0.330% at 20 °C, 0.381% at 50 °C, 0.448% at 70 °C, and 0.473% at 90 °C, respectively. This observation suggests that the coupled effect of temperature and pore water pressure has caused a certain level of damage to the rock. Furthermore, the proposed creep model effectively captured characteristics subjected to coupling effects of thermo-hydro-mechanical factors. The results provide a relevant reference value for the theoretical study of the creep mechanical behavior of rocks in multi-field environments.
... The test configuration consisted of two identical layers of simulated gouges sandwiched between three granite forcing blocks: a central block and two stationary side blocks (e.g. Marone 1998a; Zhang et al. 2019;Violay et al. 2021). Two hydraulic jacks in horizontal direction were used to apply loads normal to the granite, while a vertical hydraulic jack was used to apply shear load at designed shear rate. ...
Slide-hold-slide (SHS) test is an essential experimental approach for studying the frictional stability of faults. The origin SHS framework was established based on a consistent constant normal stress, which cannot truly reflect the stress disturbance around fault zones. In this paper, we conducted a series of ‘dynamic SHS tests’, which includes normal stress oscillations in the relaxation stage with different oscillation amplitudes and frequencies on synthetic quartz gouge using a double direct shear assembly. The experimental results reveal that the amplitude of the normal load oscillation has a remarkable effect on the frictional relaxation and healing patterns. However, the frequency of the normal load oscillation has a minor effect. Additionally, the shear loading rate is proportional to the normal loading rate during the relaxation stage, and the normal stiffness of the quartz layer remains nearly constant under various loading conditions. The creep rate during the hold phase is not obviously affected by the normal load oscillation, while the precursory slip is also sensitive to the oscillation amplitude. This study provides insights into the evolution of frictional stability in discontinuities and is beneficial for controlling relative disasters in fault zones.
... Importantly, the laboratory discovery of the stick-slip phenomenon initiated the modern era in explaining the mechanism of earthquakes through frictional stability instead of frictional strength. Specifically, rock frictional properties are measured using four types of experimental setups (Scholz, 2002;Violay et al., 2021;Fang and Wu, 2022), including direct shear (Esaki et al., 1999;Faoro et al., 2009;Fang et al., 2017;Ishibashi et al. 2018, Zhao et al., 2018aCebry and McLaskey 2021), double direct-shear (Dieterich, 1972;Marone, 1998a;Mair et al., 2002;Ikari et al., 2011;Collettini et al., 2014;Giorgetti et al., 2015;Leeman et al., 2016;Scuderi and Collettini, 2018), ring (or rotary) shear (Shimamoto, 1994;Zhang et al., 1999;Ujiie and Tsutsumi, 2010;Tatone and Grasselli, 2015;Zhao et al., 2018b;Cornelio et al., 2019), and triaxial shear (Jaeger, 1959;Byerlee, 1967;Handin, 1969;Tembe et al., 2010;Kohli and Zoback, 2013;Zhong et al., 2016;Wu et al., 2017;Ye and Ghassemi, 2018;Jia et al., 2020a;Wang et al., 2020;Ji et al., 2021a;Wang et al., 2021). For those different methods, each has its own advantages and disadvantages (Table 1). ...
... The direct shear test is simple in structure and suitable for large specimens, but contains a moment so that the normal stress is not constant over the surface The double direct-shear test has two sliding surfaces, and it is widely applied in friction tests for both rock and gouge. However, it also contains a moment that results in nonuniform normal stress Dieterich (1972); Marone (1998a); Mair et al. (2002); Ikari et al. (2011);Violay et al. (2021) Rotary shear The rotary shear apparatus is particularly suitable for producing large displacements at high slip velocities, but tangential velocity is inconsistent at different radius of the sample Tullis and Weeks (1986); Shimamoto (1994); Di Toro et al. (2010Toro et al. ( , 2011Ma et al. (2014) Triaxial shear ...
The frictional strength and sliding stability of faults are crucial in interpreting earthquake mechanisms and cycles. Herein, we report friction experiments on basalt fractures, using a self-designed triaxial apparatus that allows direct shear of samples under coupled hydro-mechanical conditions. Velocity-stepping (VS) and slide-hold-slide (SHS) experiments are performed on both bare and gouge-bearing surfaces of Xiashan basalt subjected to cyclic shear velocities at 1–30 μm/s, effective normal stresses of 1–5 MPa, and pore pressures of 70–300 kPa. The measured basalt friction coefficients are in the range of 0.67–0.74, which is sensitive to gouge thickness, normal stress, and water. Specifically, a reduction in friction coefficient is observed with an increment in gouge thickness, normal stress, and pore pressure. Based on the microscopic observation of the pre- and post-shearing sliding surfaces, this weakening effect in friction coefficient can be attributed to powder lubrication. Furthermore, the VS test results reveal predominantly velocity-strengthening behavior at investigated slip velocities, and this velocity strengthening behavior does not appear to be influenced by variations in normal stress, gouge thickness, and water. However, changes in sliding velocity and normal stress can lead to a shift between stable and unstable sliding. Specifically, stable sliding is favored by high sliding velocities and low normal stress applied in this study. Finally, we analyze the experimental data by calculating the rate-and-state parameters using the rate- and state-dependent friction (RSF) theory. Importantly, the calculated friction rate parameter (a-b) supports the velocity-strengthening behavior. Both frictional relaxation (Δμc) during hold periods and frictional healing (Δμ) upon re-shearing are linearly proportional to the logarithmic hold time, which may be attributed to the growth in true contact area with hold time. This study sheds light on the roles of sliding velocity, and gouge thickness in controlling frictional strength and stability of basalt fractures.
... With the progress of instrument industry, related products (triaxial loading apparatus, direct shear apparatus, double shear apparatus, rotation shear apparatus, etc.) have been developed in the recent past [7][8][9][10][11][12][13][14][15], and different shear methods help us to explore the shear properties of geotechnical materials under various conditions [16][17][18][19]. The development of advanced laboratory shearing apparatus is also becoming essential. ...
... Note that multiple servo commands can be added to a single experiment in chronological order. The VS (velocity stepping) and SHS (slide-hold-slide) experiments, which are very important in solid earth geophysics [2,15], can be realized owing to the highly sensitive control units in our equipment. The shear speed can abruptly adjust, and the shear box can also remain stationary for a long time at a certain displacement. ...
... Temperature effects on the frictional parameters of faults [4,35], so we will further upgrade this device with temperature control unit [15]. Moreover, for solid surface friction, acoustic emission (AE) phenomenon is an important research item [36][37][38], so the AE receivers will attach to the shear boxes in the future. ...
In this paper, we report a new multi-function servo control dynamic shear test apparatus, DJZ-500. This apparatus consists of five parts, including power system, loading frame, servo control unit, cooling system and PC console. The normal load and shear load are measured by load cells with an accuracy of 0.1 kN; normal and shear displacement are measured by LVDTs with an accuracy of 0.1 μm. DJZ-500 has the dynamic and static loading modules, which can perform the force and displacement servo control experiments in both vertical and horizontal directions. In addition, the dynamic loading modules can execute the custom waveforms, which can be utilized to investigate the seismic response of rock and soil masses. We presented six sets of representative tests on sands to demonstrate these functions. Moreover, DJZ-500 can also preform the coupled shear-flow test with the pumping system to investigate the flow behavior in sheared rock fractures. This device makes up for the deficiency of the existing equipment, and promotes the study of frictional properties of geomaterials.
... The horizontal (i.e., normal) and vertical (i.e., shear) displacements are measured with optical encoders having a resolution of 5 nm. For more details on the experimental apparatus, see Violay et al. 54 After placing the samples in the sample holders ( Fig. 2cM and O) and positioning them in the biaxial apparatus, the normal stress was raised slowly at 1 MPa/min up to 5 MPa. Then, the shear stress was increased by applying a constant displacement rate on the vertical piston at 1 μm/ s. ...
Water presence causes a dramatic reduction of sandstone strength. Under compressive stress conditions, the strength of a rock sample is controlled by frictional parameters and the fracture toughness of the material. Here, we report fracture toughness, frictional and uniaxial compression tests performed on five sandstones under dry and water-saturated conditions, that provide new insight into the mechanical influence of water on sandstone strength. The mechanical data show that water saturation causes a reduction of i) the fracture toughness and fracture energy ranging from 6 to 35% and 21-52%, respectively; and ii) the static friction coefficient ranging from 0 to 19%. The results suggest that the water weakening in sandstones (with a reduction of the uniaxial compression strength ranging from 0 to 30%) is due to the reduction of the fracture toughness and of the static friction coefficient of the materials. The measured fracture toughness and frictional parameters are then introduced into two micro-mechanical models (a pore-emanating cracks model and a wing crack model) to predict the water weakening. It is shown that the models predict the water weakening relatively well with a general slight overestimation (10-20%). Finally, a parametric analysis on the wing crack model revealed that a sandstone's absolute strength can be estimated by means of combined physical and mechanical parameter measurements.
To more accurately determine the mechanical behavior of geomaterials exposed to different stress conditions, we developed a novel three-directional servo-controlled loading apparatus, the “DWZ-250”, which could apply static or dynamic loads in the two horizontal and one vertical directions. DWZ-250 system consisted of a loading frame, a servo-controlled system, and a PC console. The loading frame had three loading pistons, two in the horizontal direction and one in the vertical direction. The servo-controlled system had static and dynamic modules that supplied either static or dynamic forces of up to 250 kN or a positive or negative velocity for each piston of up to 50 mm/min. The forces were recorded by load cells, and the displacements were recorded by linear variable differential transformers (LVDTs). The PC console consisted of a terminal controller, which included an advanced bespoke control software package “Dex.MulTest.2020”, which performed all operations and met data storage requirements. The DWZ-250 system performed static/dynamic uniaxial compression, bi-directional compression, static/dynamic double shear, slide hold slide, velocity stepping tests, etc. This new system did not have the limitations of existing devices and provided new strategies for performing a geomechanical investigation.
