Journal of Rock Mechanics and Geotechnical Engineering

Journal: Journal of Rock Mechanics and Geotechnical Engineering

Publisher

Elsevier

ISSN

1674-7755
2589-0417

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Publications 1 - 10 of 19

A methodology to determine the elastic properties of anisotropic rocks from a single uniaxial compression test
Nejati, Morteza; Dambly, Marie Luise Texas; Saar, Martin O. (2019)
Journal of Rock Mechanics and Geotechnical Engineering
This paper introduces a new methodology to measure the elastic constants of transversely isotropic rocks from a single uniaxial compression test. We first give the mathematical proof that a uniaxial compression test provides only four independent strain equations. As a result, the exact determination of all five independent elastic constants from only one test is not possible. An approximate determination of the Young’s moduli and the Poisson’s ratios is however practical and efficient when adding the Saint-Venant relation as the fifth equation. Explicit formulae are then developed to calculate both secant and tangent definitions of the five elastic constants from a minimum of four strain measurements. The results of this new methodology applied on three granitic samples demonstrate a significant stress-induced nonlinear behavior, where the tangent moduli increase by a factor of three to four when the rock is loaded up to 20 MPa. The static elastic constants obtained from the uniaxial compression test are also found to be significantly smaller than the dynamic ones obtained from the ultrasonic measurements.
Design issues for compressed air energy storage in sealed underground cavities
Perazzelli, Paolo; Anagnostou, Georgios (2016)
Journal of Rock Mechanics and Geotechnical Engineering
Compressed air energy storage (CAES) systems represent a new technology for storing very large amount of energy. A peculiarity of the systems is that gas must be stored under a high pressure (p = 10–30 MPa). A lined rock cavern (LRC) in the form of a tunnel or shaft can be used within this pressure range. The rock mass surrounding the opening resists the internal pressure and the lining ensures gas tightness. The present paper investigates the key aspects of technical feasibility of shallow LRC tunnels or shafts under a wide range of geotechnical conditions. Results show that the safety with respect to uplift failure of the rock mass is a necessary but not a sufficient condition for assessing feasibility. The deformation of the rock mass should also be kept sufficiently small to preserve the integrity of the lining and, especially, its tightness. If the rock is not sufficiently stiff, buckling or fatigue failure of the steel lining becomes more decisive when evaluating the feasible operating air pressure. The design of the concrete plug that seals the compressed air stored in the container is another demanding task. Numerical analyses indicate that in most cases, the stability of the rock mass under the plug loading is not a decisive factor for plug design.
A numerical case study on the long-term seismic assessment of reinforced concrete tunnels in corrosive environments
Antoniou, Maria; Mantakas, Antonios; Nikitas, Nikolaos; et al. (2023)
Journal of Rock Mechanics and Geotechnical Engineering
The paper investigates the long-term seismic behaviour of an underground reinforced concrete (RC) metro tunnel in Santiago, Chile, considering the combined effects of chloride-induced corrosion and cumulative, low-amplitude seismic shaking on the structure's performance. The soil-tunnel response is evaluated with the aid of transient, nonlinear finite element analysis using a two-dimensional (2D) plane strain numerical model that adopts advanced nonlinear models for the simulation of soil and concrete plasticity and the dynamic stiffness behaviour. The effects of corrosion deterioration are demonstrated in terms of time-dependent loss of rebar area and cover concrete stiffness and strength. The study illustrates the influence of ageing and repeated seismic shaking on lining deformation, crack development, and the modal characteristics of the intact and degrading systems. The results indicate that multiple low-amplitude events drive the non-degrading RC tunnel beyond its elastic regime without significant structural response consequences. A noticeable impact of corrosion deterioration on the structure's seismic performance is revealed, increasing with the number and intensity of earthquake events. Two different tunnel embedment depths are comparatively assessed. The analyses demonstrate larger co-seismic section convergence in the case of the deeper tunnel, yet a less pronounced effect of ageing and successive seismic loading compared to the shallow section, which is evident in the RC lining cracks at the end of shaking.
Tensile strength and failure behavior of rock-mortar interfaces: Direct and indirect measurements
Shams, Ghasem; Rivard, Patrice; Moradian, Omid (2024)
Journal of Rock Mechanics and Geotechnical Engineering
The tensile strength at the rock-concrete interface is one of the crucial factors controlling the failure mechanisms of structures, such as concrete gravity dams. Despite the critical importance of the failure mechanism and tensile strength of rock-concrete interfaces, understanding of these factors remains very limited. This study investigated the tensile strength and fracturing processes at rock-mortar interfaces subjected to direct and indirect tensile loadings. Digital image correlation (DIC) and acoustic emission (AE) techniques were used to monitor the failure mechanisms of specimens subjected to direct tension and indirect loading (Brazilian tests). The results indicated that the direct tensile strength of the rock-mortar specimens was lower than their indirect tensile strength, with a direct/indirect tensile strength ratio of 65%. DIC strain field data and moment tensor inversions (MTI) of AE events indicated that a significant number of shear microcracks occurred in the specimens subjected to the Brazilian test. The presence of these shear microcracks, which require more energy to break, resulted in a higher tensile strength during the Brazilian tests. In contrast, microcracks were predominantly tensile in specimens subjected to direct tension, leading to a lower tensile strength. Spatiotemporal monitoring of the cracking processes in the rock-mortar interfaces revealed that they show AE precursors before failure under the Brazilian test, whereas they show a minimal number of AE events before failure under direct tension. Due to different microcracking mechanisms, specimens tested under Brazilian tests showed lower roughness with flatter fracture surfaces than those tested under direct tension with jagged and rough fracture surfaces. The results of this study shed light on better understanding the micromechanics of damage in the rock-concrete interfaces for a safer design of engineering structures.
Effects of in situ stress measurement uncertainties on assessment of predicted seismic activity and risk associated with a hypothetical industrial-scale geologic CO2 sequestration operation
Jeanne, Pierre; Rutqvist, Jonny; Wainwright, Haruko M.; et al. (2016)
Journal of Rock Mechanics and Geotechnical Engineering
Carbon capture and storage (CCS) in geologic formations has been recognized as a promising option for reducing carbon dioxide (CO2) emissions from large stationary sources. However, the pressure buildup inside the storage formation can potentially induce slip along preexisting faults, which could lead to felt seismic ground motion and also provide pathways for brine/CO2 leakage into shallow drinking water aquifers. To assess the geomechanical stability of faults, it is of crucial importance to know the in situ state of stress. In situ stress measurements can provide some information on the stresses acting on faults but with considerable uncertainties. In this paper, we investigate how such uncertainties, as defined by the variation of stress measurements obtained within the study area, could influence the assessment of the geomechanical stability of faults and the characteristics of potential injection-induced seismic events. Our modeling study is based on a hypothetical industrial-scale carbon sequestration project assumed to be located in the Southern San Joaquin Basin in California, USA. We assess the stability on the major (25 km long) fault that bounds the sequestration site and is subjected to significant reservoir pressure changes as a result of 50 years of CO2 injection. We present a series of geomechanical simulations in which the resolved stresses on the fault were varied over ranges of values corresponding to various stress measurements performed around the study area. The simulation results are analyzed by a statistical approach. Our main results are that the variations in resolved stresses as defined by the range of stress measurements had a negligible effect on the prediction of the seismic risk (maximum magnitude), but an important effect on the timing, the seismicity rate (number of seismic events) and the location of seismic activity.
Combined approach of poroelastic and earthquake nucleation applied to the reservoir-induced seismic activity in the Val d’Agri area, Italy
Rinaldi, Antonio Pio; Improta, Luigi; Hainzl, Sebastian; et al. (2020)
Journal of Rock Mechanics and Geotechnical Engineering
In this work, an approach is developed to study the seismicity associated with the impoundment and level changes of a water reservoir (reservoir induced seismicity – RIS). The proposed methodology features a combination of a semi-analytical poroelastic model with an earthquake nucleation approach based on rate-and-state frictional law. The combined approach was applied to the case of the Pertusillo Lake, located in the Val d’Agri area (Italy), whose large seasonal water level changes are believed to induce protracted micro-seismicity (local magnitude ML < 3). Results show that the lake impoundment in 1962 could have produced up to 0.5 bar (1 bar = 100 kPa) changes in Coulomb failure stress (ΔCFS), while the seasonal water level variation is responsible for variation up to 0.05 bar. Modeling results of the seismicity rates in 2001−2014 show that the observed earthquakes are well correlated with the modeled ΔCFS. Finally, the reason that the seismicity is only observed at southwest of the Pertusillo Lake is provided, which is likely attributed to different rock lithologies and depletion caused by significant hydrocarbon exploitation in the northeastern sector of the lake.
Effect of squeezing on construction and structural safety of the Swiss high-level radioactive waste repository drifts
Nordas, Alexandros; Natale, Matteo; Cantieni, Linard; et al. (2024)
Journal of Rock Mechanics and Geotechnical Engineering
The deep geological repository for radioactive waste in Switzerland will be embedded in an approximately 100 m thick layer of Opalinus Clay. The emplacement drifts for high-level waste (approximately 3.5 m diameter) are planned to be excavated with a shielded tunnel boring machine (TBM) and supported by a segmental lining. At the repository depth of 900 m in the designated siting region Nördlich Lägern, squeezing conditions may be encountered due to the rock strength and the high hydrostatic pressure (90 bar). This paper presents a detailed assessment of the shield jamming and lining overstressing hazards, considering a stiff lining (resistance principle) and a deformable lining (yielding principle), and proposes conceptual design solutions. The assessment is based on three-dimensional transient hydromechanical simulations, which additionally consider the effects of ground anisotropy and the desaturation that may occur under negative pore pressures generated during the drift excavation. By addressing these design issues, the paper takes the opportunity to analyse some more fundamental aspects related to the influences of anisotropy and desaturation on the development of rock convergences and pressures over time, and their markedly different effects on the two lining systems. The results demonstrate that, regardless of these effects, shield jamming can be avoided with a moderate TBM overcut, however overstressing of a stiff lining may be critical depending on whether the ground desaturates. This uncertainty is eliminated using a deformable system with reasonable dimensions of yielding elements, which can also accommodate thermal strains generated due to the high temperature of the disposal canisters.
An analytical solution for the undrainedground response to tunnelling considering the excavation-induced desaturation
Nordas, Alexandros; Cantieni, Linard; Anagnostou, Georgios (2025)
Journal of Rock Mechanics and Geotechnical Engineering
When tunnelling through low-permeability saturated ground, the pore pressure decreases in the vicinity of the cavity. In certain instances of deep tunnels crossing weak rocks, the pore pressure may even become negative. All existing analytical solutions for the undrained ground response curve (GRC) in the literature assume that the ground fully retains its saturation, in which case the development of negative pore pressures has a stabilising effect – it results in increased effective stresses, and thus shearing resistance, which in turn leads to reduced deformations and plastification. In practice, however, negative pore pressures can induce partial or complete ground desaturation, which may even invalidate the premise of undrained conditions and lead to considerably increased deformations and plastification. In such cases, existing solutions are unsafe for design. The present paper aims to address this shortcoming, by presenting a novel analytical solution for the undrained GRC which incorporates the effect of the excavation-induced desaturation. The solution is derived under the assumption that the ground desaturates completely and immediately under negative pore pressures, which provides the upper bound of deformations and plastification for cases of partial desaturation. The rock is considered to be a linear elastic, brittle-plastic material, obeying a non-associated Mohr-Coulomb (MC) yield criterion. Nevertheless, the solution is also applicable to perfectly plastic rocks via a simple modification of the input parameters. Although the solution is in general semi-analytical, simple closed-form expressions are obtained in the special case of non-dilatant rocks. These expressions are also applicable to rocks exhibiting limited dilatancy, which is usually the case. An application example, based on the planned deep geological repository for radioactive waste in Switzerland, demonstrates the significant practical value and usefulness of the novel solution and underscores its necessity in cases where existing solutions that disregard desaturation are rendered thoroughly unsafe for design.
A numerical investigation into key factors controlling hard rock excavation via electropulse stimulation
Vogler, Daniel; Walsh, Stuart D.C.; Saar, Martin O. (2020)
Journal of Rock Mechanics and Geotechnical Engineering
Electropulse stimulation provides an energy-efficient means of excavating hard rocks through repeated application of high voltage pulses to the rock surface. As such, it has the potential to confer significant advantages to mining and drilling operations for mineral and energy resources. Nevertheless, before these benefits can be realized, a better understanding of these processes is required to improve their deployment in the field. In this paper, we employ a recently developed model of the grain-scale processes involved in electropulse stimulation to examine excavation of hard rock under realistic operating conditions. To that end, we investigate the maximum applied voltage within ranges of 120–600 kV, to observe the onset of rock fragmentation. We further study the effect of grain size on rock breakage, by comparing fine (granodiorite) and coarse grained (granite) rocks. Lastly, the pore fluid salinity is investigated, since the electric conductivity of the pore fluid is shown to be a governing factor for the electrical conductivity of the modeled system. This study demonstrates that all investigated factors are crucial to the efficiency of rock fragmentation by electropulsing.
Hydro-mechanical fault reactivation modeling based on elasto-plasticity with embedded weakness planes
Urpi, Luca; Graupner, Bastian; Wang, Wenqing; et al. (2020)
Journal of Rock Mechanics and Geotechnical Engineering
In this paper, an elasto-plastic constitutive model is employed to capture the shear failure that may occur in a rock mass presenting mechanical discontinuities, such as faults, fractures, bedding planes or other planar weak structures. The failure may occur in two modes: a sliding failure on the weak plane or an intrinsic failure of the rock mass. The rock matrix is expected to behave elastically or fail in a brittle manner, being represented by a non-associated Mohr-Coulomb behavior, while the sliding failure is represented by the evaluation of the Coulomb criterion on an explicitly defined plane. Failure may furthermore affect the hydraulic properties of the rock mass: the shearing of the weakness plane may create a transmissive fluid pathway. Verification of the mechanical submodel is conducted by comparison with an analytical solution, while the coupled hydro-mechanical behavior is validated with field data and will be applied within a model and code validation initiative. The work presented here aims at documenting the progress in code development, while accurate match of the field data with the numerical results is current work in progress.

Publications 1 - 10 of 19

Journal: Journal of Rock Mechanics and Geotechnical Engineering

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