| 1. |
- Aladejare, Adeyemi Emman, et al.
(författare)
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Performance analysis of empirical models for predicting rock mass deformation modulus using regression and Bayesian methods
- 2020
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 12:6, s. 1263-1271
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Tidskriftsartikel (refereegranskat)abstract
- Deformation modulus of rock mass is one of the input parameters to most rock engineering designs and constructions. The field tests for determination of deformation modulus are cumbersome, expensive and time-consuming. This has prompted the development of various regression equations to estimate deformation modulus from results of rock mass classifications, with rock mass rating (RMR) being one of the frequently used classifications. The regression equations are of different types ranging from linear to nonlinear functions like power and exponential. Bayesian method has recently been developed to incorporate regression equations into a Bayesian framework to provide better estimates of geotechnical properties. The question of whether Bayesian method improves the estimation of geotechnical properties in all circumstances remains open. Therefore, a comparative study was conducted to assess the performances of regression and Bayesian methods when they are used to characterize deformation modulus from the same set of RMR data obtained from two project sites. The study also investigated the performance of different types of regression equations in estimation of the deformation modulus. Statistics, probability distributions and prediction indicators were used to assess the performances of regression and Bayesian methods and different types of regression equations. It was found that power and exponential types of regression equations provide a better estimate than linear regression equations. In addition, it was discovered that the ability of the Bayesian method to provide better estimates of deformation modulus than regression method depends on the quality and quantity of input data as well as the type of the regression equation.
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| 2. |
- Bista, Dipen, et al.
(författare)
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Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load
- 2020
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 12:3, s. 449-460
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Tidskriftsartikel (refereegranskat)abstract
- The location and geometry of large-scale asperity present at the foundation of concrete gravity dams and buttress dams affect the shear resistance of the concrete-rock interface. However, the parameters describing the frictional resistance of the interface usually do not account for these asperities. This could result in an underestimate of the peak shear strength, which leads to significantly conservative design for new dams or unnecessary stability enhancing measures for existing ones. The aim of this work was to investigate the effect of the location of first-order asperity on the peak shear strength of a concrete-rock interface under eccentric load and the model discrepancy associated with the commonly used rigid body methods for calculating the factor of safety (FS) against sliding. For this, a series of direct and eccentric shear tests under constant normal load (CNL) was carried out on concrete-rock samples. The peak shear strengths measured in the tests were compared in terms of asperity location and with the predicted values from analytical rigid body methods. The results showed that the large-scale asperity under eccentric load significantly affected the peak shear strength. Furthermore, unlike the conventional assumption of sliding or shear failure of an asperity in direct shear, under the effect of eccentric shear load, a tensile failure in the rock or in the concrete could occur, resulting in a lower shear strength compared with that of direct shear tests. These results could have important implications for assessment of the FS against sliding failure in the concrete-rock interface.
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| 3. |
- Bista, Dipen, et al.
(författare)
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Numerical parametric study on the influence of location and inclination of large-scale asperities on the shear strength of concrete-rock interfaces of small buttress dams
- 2024
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755.
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Tidskriftsartikel (refereegranskat)abstract
- When assessing the sliding stability of a concrete dam, the influence of large-scale asperities in the sliding plane is often ignored due to limitations of the analytical rigid body assessment methods provided by current dam assessment guidelines. However, these asperities can potentially improve the load capacity of a concrete dam in terms of sliding stability. Although their influence in a sliding plane has been thoroughly studied for direct shear, their influence under eccentric loading, as in the case of dams, is unknown. This paper presents the results of a parametric study that used finite element analysis (FEA) to investigate the influence of large-scale asperities on the load capacity of small buttress dams. By varying the inclination and location of an asperity located in the concrete-rock interface along with the strength of the rock foundation material, transitions between different failure modes and correlations between the load capacity and the varied parameters were observed. The results indicated that the inclination of the asperity had a significant impact on the failure mode. When the inclination was 30° and greater, interlocking occurred between the dam and foundation and the governing failure modes were either rupture of the dam body or asperity. When the asperity inclination was significant enough to provide interlocking, the load capacity of the dam was impacted by the strength of the rock in the foundation through influencing the load capacity of the asperity. The location of the asperity along the concrete-rock interface did not affect the failure mode, except for when the asperity was located at the toe of the dam, but had an influence on the load capacity when the failure occurred by rupture of the buttress or by sliding. By accounting for a single large-scale asperity in the concrete-rock interface of the analysed dam, a horizontal load capacity increase of 30%–160% was obtained, depending on the inclination and location of the asperity and the strength of the foundation material.
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| 4. |
- Castro-Filgueira, Uxia, et al.
(författare)
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Particle flow code simulation of intact and fissured granitic rock samples
- 2020
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 12:5, s. 960-974
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a calibration process of three-dimensional particle flow code (PFC3D) simulation of intact and fissured granite samples. First, laboratory stress-strain response from triaxial testing of intact and fissured granite samples is recalled. Then, PFC3D is introduced, with focus on the bonded particle models (BPM). After that, we present previous studies where intact rock is simulated by means of flat-joint approaches, and how improved accuracy was gained with the help of parametric studies. Then, models of the pre-fissured rock specimens were generated, including modeled fissures in the form of "smooth joint" type contacts. Finally, triaxial testing simulations of 1 + 2 and 2 + 3 jointed rock specimens were performed. Results show that both elastic behavior and the peak strength levels are closely matched, without any additional fine tuning of micro-mechanical parameters. Concerning the post-failure behavior, models reproduce the trends of decreasing dilation with increasing confinement and plasticity. However, the dilation values simulated are larger than those observed in practice. This is attributed to the difficulty in modeling some phenomena of fissured rock behaviors, such as rock piece corner crushing with dust production and interactions between newly formed shear bands or axial splitting cracks with pre-existing joints.
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| 5. |
- Damasceno, Davi Rodrigues, et al.
(författare)
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Effect of rock joints on lined rock caverns subjected to high internal gas pressure
- 2023
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 15:7, s. 1625-1635
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Tidskriftsartikel (refereegranskat)abstract
- The storage of hydrogen gas in lined rock caverns (LRCs) may enable the implementation of the first large-scale fossil-free steelmaking process in Sweden, but filling such storage causes joints in the rock mass to open, concentrating strains in the lining. The structural interaction between the LRC components must be able to reduce the strain concentration in the sealing steel lining; however, this interaction is complex and difficult to predict with analytical methods. In this paper, the strain concentration in LRCs from the opening of rock joints is studied using finite element (FE) analyses, where the large- and small-scale behaviors of the LRC are coupled. The model also includes concrete crack initiation and development with increasing gas pressure and rock joint width. The interaction between the jointed rock mass and the reinforced concrete, the sliding layer, and the steel lining is demonstrated. The results show that the rock mass quality and the spacing of the rock joints have the greatest influence on the strain distributions in the steel lining. The largest effect of rock joints on the maximum strains in the steel lining was observed for geological conditions of “good” quality rock masses.
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| 6. |
- Damasceno, Davi Rodrigues, et al.
(författare)
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Rock mass response for lined rock caverns subjected to high internal gas pressure
- 2023
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 15:1, s. 119-129
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Tidskriftsartikel (refereegranskat)abstract
- The storage of hydrogen gas in underground lined rock caverns (LRCs) enables the implementation of the first fossil-free steelmaking process to meet the large demand for crude steel. Predicting the response of rock mass is important to ensure that gas leakage due to rupture of the steel lining does not occur. Analytical and numerical models can be used to estimate the rock mass response to high internal pressure; however, the fitness of these models under different in situ stress conditions and cavern shapes has not been studied. In this paper, the suitability of analytical and numerical models to estimate the maximum cavern wall tangential strain under high internal pressure is studied. The analytical model is derived in detail and finite element (FE) models considering both two-dimensional (2D) and three-dimensional (3D) geometries are presented. These models are verified with field measurements from the LRC in Skallen, southwestern Sweden. The analytical model is inexpensive to implement and gives good results for isotropic in situ stress conditions and large cavern heights. For the case of anisotropic horizontal in situ stresses, as the conditions in Skallen, the 3D FE model is the best approach.
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| 7. |
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| 8. |
- Krounis Guerrero, Alexandra, et al.
(författare)
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Effects of spatial variation in cohesion over the concrete-rock interface on dam sliding stability
- 2015
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Kexue Chubanshe. - 1674-7755. ; 7:6, s. 659-667
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Tidskriftsartikel (refereegranskat)abstract
- The limit equilibrium method (LEM) is widely used for sliding stability evaluation of concrete gravity dams. Failure is then commonly assumed to occur along the entire sliding surface simultaneously. However, the brittle behaviour of bonded concrete-rock contacts, in combination with the varying stress over the interface, implies that the failure of bonded dam-foundation interfaces occurs progressively. In addition, the spatial variation in cohesion may introduce weak spots where failure can be initiated. Nonetheless, the combined effect of brittle failure and spatial variation in cohesion on the overall shear strength of the interface has not been studied previously. In this paper, numerical analyses are used to investigate the effect of brittle failure in combination with spatial variation in cohesion that is taken into account by random fields with different correlation lengths. The study concludes that a possible existence of weak spots along the interface has to be considered since it significantly reduces the overall shear strength of the interface, and implications for doing so are discussed.
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| 9. |
- Larsson, Jörgen, et al.
(författare)
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A novel method for geometric quality assurance of rock joint replicas in direct shear testing – Part 1 : Derivation of quality assurance parameters and geometric reproducibility
- 2023
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Chinese Academy of Sciences. - 1674-7755. ; 15:9, s. 2193-
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Tidskriftsartikel (refereegranskat)abstract
- Since each rock joint is unique by nature, the utilization of replicas in direct shear testing is required to carry out experimental parameter studies. However, information about the ability of the replicas to simulate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking. With the aim to facilitate generation of high-quality direct shear test data from replicas, a novel component in the testing procedure is introduced by presenting two parameters for geometric quality assurance. The parameters are derived from surface comparisons of three-dimensional (3D) scanning data of the rock joint and its replicas. The first parameter, σmf, captures morphological deviations between the replica and the rock joint surfaces. σmf is derived as the standard deviation of the deviations between the coordinate points of the replica and the rock joint. Four sources of errors introduced in the replica manufacturing process employed in this study could be identified. These errors could be minimized, yielding replicas with σmf ≤ 0.06 mm. The second parameter is a vector, VHp100, which describes deviations with respect to the shear direction. It is the projection of the 100 mm long normal vector of the best-fit plane of the replica joint surface to the corresponding plane of the rock joint. |VHp100| was found to be less than or equal to 0.36 mm in this study. Application of these two geometric quality assurance parameters demonstrates that it is possible to manufacture replicas with high geometric similarity to the rock joint. In a subsequent paper (part 2), σmf and VHp100 are incorporated in a novel quality assurance method, in which the parameters shall be evaluated prior to direct shear testing. Replicas having parameter values below established thresholds shall have a known and narrow dispersion and imitate the shear mechanical behavior of the rock joint.
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| 10. |
- Larsson, Jörgen, et al.
(författare)
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A novel method for geometric quality assurance of rock joint replicas in direct shear testing : Part 2 : Validation and mechanical replicability
- 2023
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Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 15, s. 2209-
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Tidskriftsartikel (refereegranskat)abstract
- Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies. However, a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking. In this study, a novel method is presented for geometric quality assurance of replicas. The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results. In Part 1 of this study, two quality assurance parameters, σmf and VHp100, are derived and their usefulness for evaluation of geometric deviations, i.e. geometric reproducibility, is shown. In Part 2, the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior, which qualifies the parameters for usage in the quality assurance method. Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σmf < 0.06 mm and < 0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength. The wear in these replicas, which have similar morphology as the rock joint, is in the same areas as in the rock joint. The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties, possibly from differences in toughness. It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics, which makes them useful in parameter studies.
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