Characterization of roughness and shear behavior of thermally treated granite fractures
TL;DR: In this article, the authors measured the uniaxial compression strength (UCS) and p-wave velocity (Vp) of granite samples after they were heated to various temperatures as high as 500°C and allowed to cool to room temperature.
About: This article is published in Engineering Geology.The article was published on 2021-11-01. It has received 25 citations till now. The article focuses on the topics: Shear strength (discontinuity) & Direct shear test.
Citations
More filters
01 Jan 1986
TL;DR: In this paper, the effect of scale on the shear behavior of joints is studied by performing direct shear tests on different sized replicas cast from various natural joint surfaces, and it is shown that scale effects are more pronounced in the case of rough, undulating joints, whereas they are virtually absent for planar joints.
Abstract: The effect of scale on the shear behaviour of joints is studied by performing direct shear tests on different sized replicas cast from various natural joint surfaces. The result show significant scale effects on both the shear strength and deformation characteristics. Scale effects are more pronounced in the case of rough, undulating joint types, whereas they are virtually absent for planar joints. The key factor is the involvement of different asperity sizes in controlling the peak behaviour of different lengths of joints. It is shown that as a results both the joint roughness coefficient (JRC) and the joint compression strength (JCS) reduce with increasing scale. The behaviour of multiple jointed masses with different joint spacing is also considered. It is found that despite unchanged roughness, jointed masses consisting of many small blocks have higher peak shear strength than jointed masses with larger joint spacing. These scale effects are related to the changing stiffness of a rock mass as the block size or joint spacing increases or decreases. Economic methods for obtaining scale-free estimates of shear strength are described.
374 citations
TL;DR: In this article , a 2D Particle Flow Code (PFC) modeling is conducted to shed light on the failure mechanism and damage evolution of hard rock joints, especially under high stress.
Abstract: Rock joints can be subjected to high normal stress in deep rock projects such as deep mining, tunnelling, and oil and gas exploitation. The spatial and temporal damage evolution and distribution of rock joints cannot be directly observed due to the opaque nature of rocks. Discrete element modeling provides a good alternative solution to visualize the development of micro-cracks under complex geological conditions. In this study, 2D Particle Flow Code (PFC) modelling is conducted to shed light on the failure mechanism and damage evolution of hard rock joints, especially under high stress. The influence of normal stress, initial joint roughness and grain size on the shear behavior and micro-damage are examined, and the spatial and temporal distribution of micro-cracks are also compared and quantified. Results indicate that more cracks develop for a joint sheared under a higher normal stress, and a rougher joint also tends to generate more cracks. On the other hand, the spatial distribution of shear-induced micro-cracks becomes more unevenly distributed with increasing normal stress and roughness. Three stages, namely slow increase, fast increase and slow increase can be divided on the temporal cumulative crack development curve. The micro-cracks grow faster in the fast growth stage for a rougher joint sheared under a higher normal stress, which is consistent with the acoustic emission monitoring in the laboratory direct shear tests. Both peak shear strength and damage zone size are affected by the particle size, which is closely associated with the more interlocked effect of large grains on the two sides of the shear interface. The maximum length of the crack is dependent on the magnitude of contact force, rather than the shear displacement, and the maximum contact force tends to be larger for the rougher joint.
12 citations
TL;DR: In this paper , a cracked straight-through Brazilian disc (CSTBD) specimen was applied to investigate the fracture behavior of two types of rock materials (hard rock and soft rock) under high temperature, which was made of granite and green sandstone and heating temperature from 25 °C (room temperature) to 700 °C.
9 citations
TL;DR: In this paper , a new theoretical model was established to study the thermal damage evolution of CRC under high-temperature mechanical coupling conditions, and the experimental results demonstrate that the peak strength of CRC is 36.6% relative to the concrete.
6 citations
TL;DR: In this paper , the effect of thermal treatment on the mechanical properties of clay-rich rocks, such as mudstone, under three temperatures; ambient temperature, 250, and 500 °C.
Abstract: Temperature is one of the most important environmental factors that affect rock engineering properties. The clay-rich rocks such as mudstone are abundant in the earth's crust and have a high affinity to water. So the behavior of these rocks differs from others after thermal treatment, which might force the water out of the clay. Therefore, we investigated the effect of thermal treatment on the mechanical properties of clay-rich rock, mudstone, under three temperatures; ambient temperature, 250, and 500 °C. Our results showed that thermal cracks begin to appear in the mudstone at a temperature between 500 and 600 °C. Several mechanical properties were measured in the lab; uniaxial compressive strength (UCS), elastic modulus (E), Poisson's ratio (ν), Brazilian tensile strength (BTS), fracture toughness of tensile (KIC), and shear (KIIC) cracks. Due to the drying of clay minerals through the dehydration and dihydroxylation processes, the following mechanical properties of mudstone significantly increased after treating the rock with a temperature of 500 °C; UCS, E, BTS, KIC, and KIIC have improved by 91%, 39%, 16%, 41%, and 94%, respectively, while ν decreased by 80%. This reduction of ν, due to increasing the thermal treatment temperature, caused the behavior of mudstone to transform gradually from ductile to brittle material which means that the failure of such rocks, at this temperature, might be a sudden one. This research presents new insights into the effect of temperatures below 500 °C on clay-rich rocks for use in different engineering fields.
6 citations
References
More filters
01 Dec 1977
TL;DR: In this paper, the authors describe an empirical law of friction for rock joints, which can be used both for extrapolating and predicting shear strength data, and demonstrate that it can be estimated to within ± 1° for any one of the eight rock types investigated.
Abstract: The paper describes an empirical law of friction for rock joints which can be used both for extrapolating and predicting shear strength data. The equation is based on three index parameters; the joint roughness coefficientJRC, the joint wall compressive strengthJCS, and the residual friction angleφ
r
. All these index values can be measured in the laboratory. They can also be measured in the field. Index tests and subsequent shear box tests on more than 100 joint samples have demonstrated thatφ
r
can be estimated to within ± 1° for any one of the eight rock types investigated. The mean value of the peak shear strength angle (arctanτ/σ
n
) for the same 100 joints was estimated to within 1/2°. The exceptionally close prediction of peak strength is made possible by performing self-weight (low stress) sliding tests on blocks with throughgoing joints. The total friction angle (arctanτ/σ
n
) at which sliding occurs provides an estimate of the joint roughness coefficientJRC. The latter is constant over a range of effective normal stress of at least four orders of magnitude. However, it is found that bothJRC andJCS reduce with increasing joint length. Increasing the length of joint therefore reduces not only the peak shear strength, but also the peak dilation angle and the peak shear stiffness. These important scale effects can be predicted at a fraction of the cost of performing large scale in situ direct shear tests.
2,139 citations
TL;DR: The current understanding of the causes and mechanics of earthquakes caused by human activity, including injection of wastewater into deep formations and emerging technologies related to oil and gas recovery, is reviewed.
Abstract: Background Human-induced earthquakes have become an important topic of political and scientific discussion, owing to the concern that these events may be responsible for widespread damage and an overall increase in seismicity. It has long been known that impoundment of reservoirs, surface and underground mining, withdrawal of fluids and gas from the subsurface, and injection of fluids into underground formations are capable of inducing earthquakes. In particular, earthquakes caused by injection have become a focal point, as new drilling and well-completion technologies enable the extraction of oil and gas from previously unproductive formations. Earthquakes with magnitude (M) ≥ 3 in the U.S. midcontinent, 1967–2012. After decades of a steady earthquake rate (average of 21 events/year), activity increased starting in 2001 and peaked at 188 earthquakes in 2011. Human-induced earthquakes are suspected to be partially responsible for the increase. Advances Microearthquakes (that is, those with magnitudes below 2) are routinely produced as part of the hydraulic fracturing (or “fracking”) process used to stimulate the production of oil, but the process as currently practiced appears to pose a low risk of inducing destructive earthquakes. More than 100,000 wells have been subjected to fracking in recent years, and the largest induced earthquake was magnitude 3.6, which is too small to pose a serious risk. Yet, wastewater disposal by injection into deep wells poses a higher risk, because this practice can induce larger earthquakes. For example, several of the largest earthquakes in the U.S. midcontinent in 2011 and 2012 may have been triggered by nearby disposal wells. The largest of these was a magnitude 5.6 event in central Oklahoma that destroyed 14 homes and injured two people. The mechanism responsible for inducing these events appears to be the well-understood process of weakening a preexisting fault by elevating the fluid pressure. However, only a small fraction of the more than 30,000 wastewater disposal wells appears to be problematic—typically those that dispose of very large volumes of water and/or communicate pressure perturbations directly into basement faults. Outlook Injection-induced earthquakes, such as those that struck in 2011, clearly contribute to the seismic hazard. Quantifying their contribution presents difficult challenges that will require new research into the physics of induced earthquakes and the potential for inducing large-magnitude events. The petroleum industry needs clear requirements for operation, regulators must have a solid scientific basis for those requirements, and the public needs assurance that the regulations are sufficient and are being followed. The current regulatory frameworks for wastewater disposal wells were designed to protect potable water sources from contamination and do not address seismic safety. One consequence is that both the quantity and timeliness of information on injection volumes and pressures reported to regulatory agencies are far from ideal for managing earthquake risk from injection activities. In addition, seismic monitoring capabilities in many of the areas in which wastewater injection activities have increased are not capable of detecting small earthquake activity that may presage larger seismic events.
1,823 citations
TL;DR: Stick-slip often accompanies frictional sliding in laboratory experi ments with geologic materials and may represent stick slip during sliding along old or newly formed faults in the earth.
Abstract: Stick-slip often accompanies frictional sliding in laboratory experi ments with geologic materials. Shallow focus earthquakes may represent stick slip during sliding along old or newly formed faults in the earth In such a situation, observed stress drops repre sent release of a small fraction of the stress supported by the rock surround ing the earthquake focus.
868 citations
TL;DR: In this paper, the root mean square and the mean square of the first derivative of a surface profile were used to measure the joint roughness coefficient of the surface profiles presented by Barton and Choubey.
710 citations
TL;DR: In this paper, the authors present an up-to-date review of the state of knowledge about induced seismicity during the creation and operation of enhanced geothermal systems, and point out the gaps in knowledge that if addressed will allow an improved understanding of the mechanisms generating the events as well as serve as a basis to develop successful protocols for monitoring and addressing community issues associated with such induced earthquakes.
638 citations