| 1. |
- Aladejare, Adeyemi Emman, et al.
(författare)
-
Performance analysis of empirical models for predicting rock mass deformation modulus using regression and Bayesian methods
- 2020
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 12:6, s. 1263-1271
-
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.
|
|
| 2. |
- Bista, Dipen, et al.
(författare)
-
Influence of location of large-scale asperity on shear strength of concrete-rock interface under eccentric load
- 2020
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 12:3, s. 449-460
-
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.
|
|
| 3. |
- Bista, Dipen, et al.
(författare)
-
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
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755.
-
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.
|
|
| 4. |
- Castro-Filgueira, Uxia, et al.
(författare)
-
Particle flow code simulation of intact and fissured granitic rock samples
- 2020
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 12:5, s. 960-974
-
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.
|
|
| 5. |
- Damasceno, Davi Rodrigues, et al.
(författare)
-
Effect of rock joints on lined rock caverns subjected to high internal gas pressure
- 2023
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 15:7, s. 1625-1635
-
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.
|
|
| 6. |
- Damasceno, Davi Rodrigues, et al.
(författare)
-
Rock mass response for lined rock caverns subjected to high internal gas pressure
- 2023
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 15:1, s. 119-129
-
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.
|
|
| 7. |
|
|
| 8. |
- Krounis Guerrero, Alexandra, et al.
(författare)
-
Effects of spatial variation in cohesion over the concrete-rock interface on dam sliding stability
- 2015
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Kexue Chubanshe. - 1674-7755. ; 7:6, s. 659-667
-
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.
|
|
| 9. |
- Larsson, Jörgen, et al.
(författare)
-
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
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Chinese Academy of Sciences. - 1674-7755. ; 15:9, s. 2193-
-
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.
|
|
| 10. |
- Larsson, Jörgen, et al.
(författare)
-
A novel method for geometric quality assurance of rock joint replicas in direct shear testing : Part 2 : Validation and mechanical replicability
- 2023
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 15, s. 2209-
-
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.
|
|
| 11. |
- Lei, Qinghua, et al.
(författare)
-
Interactive roles of geometrical distribution and geomechanical deformation of fracture networks in fluid flow through fractured geological media
- 2020
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 12:4, s. 780-792
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the combined effects of geometrical distribution and geomechanical deformation of fracture networks on fluid flow through fractured geological media are investigated numerically. We consider a finite-sized model domain in which the geometry of fracture systems follows a power-law length scaling. The geomechanical response of the fractured rock is simulated using a hybrid finite-discrete element model, which can capture the deformation of intact rocks, the interaction of matrix blocks, the displacement of discrete fractures and the propagation of new cracks. Under far-field stress loading, the locally variable stress distribution in the fractured rock leads to a stress-dependent variable aperture field controlled by compression-induced closure and shear-induced dilatancy of rough fractures. The equivalent permeability of the deformed fractured rock is calculated by solving for the fracture-matrix flow considering the cubic relationship between fracture aperture and flow rate at each local fracture segment. We report that the geometrical connectivity of fracture networks plays a critical role in the hydromechanical processes in fractured rocks. A well-connected fracture system under a high stress ratio condition exhibits intense frictional sliding and large fracture dilation/opening, leading to greater rock mass permeability. However, a disconnected fracture network accommodates much less fracture shearing and opening, and has much lower bulk permeability. We further propose an analytical solution for the relationship between the equivalent permeability of fractured rocks and the connectivity metric (i.e. percolation parameter) of fracture networks, which yields an excellent match to the numerical results. We infer that fluid flow through a well-connected system is governed by traversing channels (forming an “in parallel” architecture) and thus equivalent permeability is sensitive to stress loading (due to stress-dependent fracture permeability), whilst fluid flow through a disconnected system is more ruled by matrix (linking isolated clusters “in series”) and has much less stress dependency.
|
|
| 12. |
- Noorian-Bidgoli, Majid, et al.
(författare)
-
Anisotropy of strength and deformability of fractured rocks
- 2014
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 6:1, s. 156-164
-
Tidskriftsartikel (refereegranskat)abstract
- Anisotropy of the strength and deformation behaviors of fractured rock masses is a crucial issue fordesign and stability assessments of rock engineering structures, due mainly to the non-uniform and nonregulargeometries of the fracture systems. However, no adequate efforts have been made to study thisissue due to the current practical impossibility of laboratory tests with samples of large volumes containingmany fractures, and the difficulty for controlling reliable initial and boundary conditions forlarge-scale in situ tests. Therefore, a reliable numerical predicting approach for evaluating anisotropy offractured rock masses is needed. The objective of this study is to systematically investigate anisotropy ofstrength and deformability of fractured rocks, which has not been conducted in the past, using a numericalmodeling method. A series of realistic two-dimensional (2D) discrete fracture network (DFN)models were established based on site investigation data, which were then loaded in different directions,using the code UDEC of discrete element method (DEM), with changing confining pressures. Numericalresults show that strength envelopes and elastic deformability parameters of tested numerical modelsare significantly anisotropic, and vary with changing axial loading and confining pressures. The resultsindicate that for design and safety assessments of rock engineering projects, the directional variations ofstrength and deformability of the fractured rock mass concerned must be treated properly with respectto the directions of in situ stresses. Traditional practice for simply positioning axial orientation of tunnelsin association with principal stress directions only may not be adequate for safety requirements.Outstanding issues of the present study and suggestions for future study are also presented.
|
|
| 13. |
- Noorian-Bidgoli, Majid, et al.
(författare)
-
Numerical evaluation of strength and deformability of fractured rocks
- 2013
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 5:6, s. 419-430
-
Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the strength and deformability of fractured rocks is important for design, construction andstability evaluation of slopes, foundations and underground excavations in civil and mining engineering.However, laboratory tests of intact rock samples cannot provide information about the strength anddeformation behaviors of fractured rock masses that include many fractures of varying sizes, orientationsand locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costlyand often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numericalpredicting using discrete element methods (DEM) is a suitable approach for such modeling because of theiradvantages of explicit representations of both fractures system geometry and their constitutive behaviorsof fractures, besides that of intact rock matrix. In this study, to generically determine the compressivestrength of fractured rock masses, a series of numerical experiments were performed on two-dimensionaldiscrete fracture network models based on the realistic geometrical and mechanical data of fracturesystems from field mapping. We used the UDEC code and a numerical servo-controlled program forcontrolling the progressive compressive loading process to avoid sudden violent failure of the models.The two loading conditions applied are similar to the standard laboratory testing for intact rock samplesin order to check possible differences caused by such loading conditions. Numerical results show thatthe strength of fractured rocks increases with the increasing confining pressure, and that deformationbehavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses andstrains obtained from these numerical experiments were used to fit the well-known Mohr-Coulomb (MC)and Hoek-Brown (H-B) failure criteria, represented by equivalent material properties defining thesetwo criteria. The results show that both criteria can provide fair estimates of the compressive strengthsfor all tested numerical models. Parameters of the elastic deformability of fractured models during elasticdeformation stages were also evaluated, and represented as equivalent Young’s modulus and Poisson’sratio as functions of lateral confining pressure. It is the first time that such systematic numerical predictingfor strength of fractured rocks was performed considering different loading conditions, with importantfindings for different behaviors of fractured rock masses, compared with testing intact rock samples undersimilar loading conditions.
|
|
| 14. |
- Noorian-Bidgoli, Majid, et al.
(författare)
-
Water pressure effects on strength and deformability of fractured rocks under low confining pressures
- 2015
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Springer Science and Business Media LLC. - 1674-7755. ; 48:3, s. 971-985
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of groundwater on strength anddeformation behavior of fractured crystalline rocks is one ofthe important issues for design, performance and safetyassessments of surface and subsurface rock engineeringproblems. However, practical difficulties make the directin situ and laboratory measurements of these properties offractured rocks impossible at present, since effects of complexfracture system hidden inside the rock masses cannot beaccurately estimated. Therefore, numerical modeling needs tobe applied. The overall objective of this paper is to deepenour understanding on the validity of the effective stressconcept, and to evaluate the effects of water pressure onstrength and deformation parameters. The approach adopteduses discrete element methods to simulate the coupled stressdeformation-flow processes in a fractured rock mass withmodel dimensions at a representative elementary volume(REV) size and realistic representation of fracture systemgeometry. The obtained numerical results demonstrate thatwater pressure has significant influence on the strength, butwith minor effects on elastic deformation parameters, comparedwith significant influence by the lateral confiningpressure. Also, the classical effective stress concept to fracturedrock can be quite different with that applied in soilmechanics. Therefore, one should be cautious when applyingthe classical effective stress concept to fractured rock media.
|
|
| 15. |
- Pan, Wenbo, et al.
(författare)
-
Earthquake-induced fracture displacements and transmissivity changes in a 3D fracture network of crystalline rock for spent nuclear fuel disposal
- 2023
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 15:9, s. 2313-2329
-
Tidskriftsartikel (refereegranskat)abstract
- During the long service period of a nuclear waste repository in crystalline rock, large earthquake(s) may occur nearby the repository site and coseismically alter the local stress field around pre-existing fractures within the geological formation. The resulting fracture normal/shear displacements may lead to fracture opening and further promote the transport of leaked radionuclides into the groundwater system. Thus, it is of central importance to analyze the consequences of potential future earthquake(s) on the hydrogeological properties of a repository site for spent nuclear fuel disposal. Based on the detailed site characterization data of the repository site at Forsmark, Sweden, we conduct a three-dimensional (3D) seismo-hydro-mechanical simulation using the 3Dimensional Distinct Element Code (3DEC). We explicitly represent a primary seismogenic fault zone and its surrounding secondary fracture network associated with a power-law size scaling and a Fisher orientation distribution. An earthquake with a magnitude of Mw = 5.6 caused by the reactivation of the primary fault zone is modeled by simulating its transient rupture propagating radially outwards from a predefined hypocenter at a specified rupture speed, with the faulting dynamics controlled by a strength weakening law. We model the coseismic response of the off-fault fracture network subject to both static and dynamic triggering effects. We further diagnose the distribution of fracture hydro-mechanical properties (e.g. mechanical/hydraulic aperture, hydraulic transmissivity) before and after the earthquake in order to quantify earthquake-induced hydraulic changes in the fracture network. It is found that earthquake-induced fracture transmissivity changes tend to follow a power-law decay with the distance to the earthquake fault. Our simulation results and insights obtained have important implications for the long-term performance assessment of nuclear waste repositories in fractured crystalline rocks.
|
|
| 16. |
- Sexton, Brian G., et al.
(författare)
-
Stone column settlement performance in structured anisotropic clays: the influence of creep
- 2016
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 8:5, s. 672-688
-
Tidskriftsartikel (refereegranskat)abstract
- The recently developed elasto-viscoplastic Creep-SCLAY1S model has been used in conjunction with PLAXIS 2D to investigate the effectiveness of vibro-replacement in a creep-prone clay. The Creep-SCLAY1S model accounts for anisotropy, bonding, and destructuration, and uses the concept of a constant rate of viscoplastic multiplier to calculate creep strain rate. A comparison of settlement improvement factors with and without creep indicates that ‘total’ settlement improvement factors (primary plus creep) are lower than their ‘primary’ counterparts (primary settlement only). The lowest settlement improvement factors arise for analyses incorporating the effect of bonding and destructuration. Examination of the variations of vertical stress with time and depth has indicated that vertical stress is transferred from the soil to the column as the soil creeps. This results in additional column yielding. In addition, the radial and hoop stresses in the soil are lower for the ‘creep’ case. The reduced radial stresses lead to additional column bulging and hence more settlement, whereas the hoop stress reductions appear to be a secondary effect, caused by additional plastic deformation for the ‘creep’ case. © 2016 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences
|
|
| 17. |
- Shahri, Abbas Abbaszadeh, et al.
(författare)
-
Spatial distribution modeling of subsurface bedrock using a developed automated intelligence deep learning procedure : A case study in Sweden
- 2021
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 13:6, s. 1300-1310
-
Tidskriftsartikel (refereegranskat)abstract
- Due to associated uncertainties, modelling the spatial distribution of depth to bedrock (DTB) is an important and challenging concern in many geo-engineering applications. The association between DTB, the safety and economy of design structures implies that generating more precise predictive models can be of vital interest. In the present study, the challenge of applying an optimally predictive three-dimensional (3D) spatial DTB model for an area in Stockholm, Sweden was addressed using an automated intelligent computing design procedure. The process was developed and programmed in both C++ and Python to track their performance in specified tasks and also to cover a wide variety of different internal characteristics and libraries. In comparison to the ordinary Kriging (OK) geostatistical tool, the superiority of the developed automated intelligence system was demonstrated through the analysis of confusion matrices and the ranked accuracies of different statistical errors. The results showed that in the absence of measured data, the intelligence models as a flexible and efficient alternative approach can account for associated uncertainties, thus creating more accurate spatial 3D models and providing an appropriate prediction at any point in the subsurface of the study area.
|
|
| 18. |
|
|
| 19. |
- Teng, Penghua, et al.
(författare)
-
Modelling erosion of a single rock block using a coupled CFD-DEM approach
- 2023
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 15:9, s. 2375-2387
-
Tidskriftsartikel (refereegranskat)abstract
- Rock block removal is the prevalent physical mechanism for rock erosion and could affect the stability of dam foundations and spillways. Despite this, understanding of block removal is still inadequate because of the complex interactions among block characteristics, hydraulic forces, and erosive processes acting on the block. Herein, based on a previously conducted physical experiment of erosion of a single rock block, the removal processes of two different protruding blocks are represented by a coupled computational fluid dynamics-discrete element model (CFD-DEM) approach under varied flow conditions. Additionally, the blocks could be rotated with respect to the flow direction to consider the effect of the discontinuity orientation on the block removal process. Simulation results visualize the entire block removal process. The simulations reproduce the effects of the discontinuity orientation on the critical flow velocity inducing block incipient motion and the trajectory of the block motion observed in the physical experiments. The numerical results present a similar tendency of the critical velocities at different discontinuity orientations but have slightly lower values. The trajectory of the block in the simulations fits well with the experimental measurements. The relationship between the dimensionless critical shear stress and discontinuity orientation observed from the simulations shows that the effect of block protrusion becomes more dominant on the block incipient motion with the increase of relative protrusion height. To our knowledge, this present study is the first attempt to use the coupled finite volume method (FVM)-DEM approach for modelling the interaction behavior between the block and the flowing water so that the block removal process can be reproduced and analyzed.
|
|
| 20. |
- Thoeni, Klaus, et al.
(författare)
-
Designing waste rock barriers by advanced numerical modelling
- 2019
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 11:3, s. 659-675
-
Tidskriftsartikel (refereegranskat)abstract
- Design of waste rock barriers forming safety berms for haul trucks requires knowledge of complex interactions which cannot readily be tested by physical means. An advanced numerical model based on non-smooth multi-domain mechanics is presented together with model calibration using limited full-scaleexperimental data. Waste rock is represented by spherical particles with rolling resistance, and an ultra-class haul truck is represented by a rigid multibody system interconnected with mechanical joints. The model components are first calibrated and then the calibrated model is used for simulating various collision scenarios with different approach conditions and safety berm geometries. Numerical predictions indicate that the width of the berm is most critical for efficiently stopping a runaway truck. The model can also predict if a certain berm geometry is capable of stopping a runaway truck. Results are summarised in a series of diagrams intended for use as design guidelines by practitioners and engineers.
|
|
| 21. |
- Wang, Liang, et al.
(författare)
-
A stable implicit nodal integration-based particle finite element method (N-PFEM) for modelling saturated soil dynamics
- 2024
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 16:6, s. 2172-2183
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we present a novel nodal integration-based particle finite element method (N-PFEM) designed for the dynamic analysis of saturated soils. Our approach incorporates the nodal integration technique into a generalised Hellinger-Reissner (HR) variational principle, creating an implicit PFEM formulation. To mitigate the volumetric locking issue in low-order elements, we employ a node-based strain smoothing technique. By discretising field variables at the centre of smoothing cells, we achieve nodal integration over cells, eliminating the need for sophisticated mapping operations after re-meshing in the PFEM. We express the discretised governing equations as a min-max optimisation problem, which is further reformulated as a standard second-order cone programming (SOCP) problem. Stresses, pore water pressure, and displacements are simultaneously determined using the advanced primal-dual interior point method. Consequently, our numerical model offers improved accuracy for stresses and pore water pressure compared to the displacement-based PFEM formulation. Numerical experiments demonstrate that the N-PFEM efficiently captures both transient and long-term hydro-mechanical behaviour of saturated soils with high accuracy, obviating the need for stabilisation or regularisation techniques commonly employed in other nodal integration-based PFEM approaches. This work holds significant implications for the development of robust and accurate numerical tools for studying saturated soil dynamics.
|
|
| 22. |
- Yu, Sihao, et al.
(författare)
-
A performance-based hybrid deep learning model for predicting TBM advance rate using Attention-ResNet-LSTM
- 2024
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 16:1, s. 65-80
-
Tidskriftsartikel (refereegranskat)abstract
- The technology of tunnel boring machine (TBM) has been widely applied for underground construction worldwide; however, how to ensure the TBM tunneling process safe and efficient remains a major concern. Advance rate is a key parameter of TBM operation and reflects the TBM-ground interaction, for which a reliable prediction helps optimize the TBM performance. Here, we develop a hybrid neural network model, called Attention-ResNet-LSTM, for accurate prediction of the TBM advance rate. A database including geological properties and TBM operational parameters from the Yangtze River Natural Gas Pipeline Project is used to train and test this deep learning model. The evolutionary polynomial regression method is adopted to aid the selection of input parameters. The results of numerical experiments show that our Attention-ResNet-LSTM model outperforms other commonly-used intelligent models with a lower root mean square error and a lower mean absolute percentage error. Further, parametric analyses are conducted to explore the effects of the sequence length of historical data and the model architecture on the prediction accuracy. A correlation analysis between the input and output parameters is also implemented to provide guidance for adjusting relevant TBM operational parameters. The performance of our hybrid intelligent model is demonstrated in a case study of TBM tunneling through a complex ground with variable strata. Finally, data collected from the Baimang River Tunnel Project in Shenzhen of China are used to further test the generalization of our model. The results indicate that, compared to the conventional ResNet-LSTM model, our model has a better predictive capability for scenarios with unknown datasets due to its self-adaptive characteristic.
|
|
| 23. |
- Zhang, Zong-Xian, et al.
(författare)
-
An empirical approach for predicting burden velocities in rock blasting
- 2021
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier. - 1674-7755. ; 13:4, s. 767-773
-
Tidskriftsartikel (refereegranskat)abstract
- An analytical relation between burden velocity and ratio of burden to blasthole diameter is developed in this paper. This relation is found to be consistent with the measured burden velocities of all 37 full-scale blasts found from published articles. These blasts include single-hole blasts, multi-hole blasts, and simultaneously-initiated blasts with various borehole diameters such as 64 mm, 76 mm, 92 mm, 115 mm, 142 mm and 310 mm. All boreholes were fully charged. The agreement between measured and calculated burden velocities demonstrates that this relation can be used to predict the burden velocity of a wide range of full-scale blast with fully-coupled explosive charge and help to determine a correct delay time between adjacent holes or rows in various full-scale blasts involved in tunnelling (or drifting), surface and underground mining production blasts and underground opening slot blasts. In addition, this theoretical relation is found to agree with the measured burden velocities of 9 laboratory small-scale blasts to a certain extent. To predict the burden velocity of a small-scale blast, a further study or modification to the relation is necessary by using more small-scale blasts in the future.
|
|
| 24. |
- Zhao, Zhihong, et al.
(författare)
-
Evaluation of hydrodynamic dispersion parameters in fractured rocks
- 2010
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - 1674-7755. ; 2, s. 243-254
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical procedure to determine the equivalent hydrodynamic dispersion coefficients and Péclet number (Pe) of a fractured rock is presented using random walk particle tracking method. The geometrical effects of fracture system on hydrodynamic dispersion are studied. The results obtained from the proposed method agree well with those of empirical models, which are the scale-dependent hydrodynamic dispersion coefficients in an asymptotic or exponential form. A variance case is added to investigate the influence of longitudinal hydrodynamic dispersion in individual fractures on the macro-hydrodynamic dispersion at the fracture network scale, and its influence is demonstrated with a verification example. In addition, we investigate the influences of directional flow and stress conditions on the behavior of hydrodynamic dispersion in fracture networks. The results show that the magnitudes of the hydrodynamic dispersion coefficients are relatively smaller when the flow direction is parallel to the dip directions of fracture sets. Compressive stresses significantly reduce hydrodynamic dispersion. However, the remaining questions are: (1) whether the deformed fracture network under high stress conditions may make the scale-dependent hydrodynamic dispersion coefficients have asymptotic or exponential forms, and (2) what the conditions for existence of a welldefined equivalent hydrodynamic dispersion tensor are. They need to be further investigated.
|
|
| 25. |
- Zhao, Zhihong, et al.
(författare)
-
Impact of stress on solute transport in a fracture network : A comparison study
- 2013
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Chinese Academy of Sciences. - 1674-7755. ; 5:2, s. 110-123
-
Tidskriftsartikel (refereegranskat)abstract
- This paper compares numerical modeling of the effect of stress on solute transport (advection and matrix diffusion) in fractured rocks in which fracture apertures are correlated with fracture lengths. It is mainly motivated by the performance and safety assessments of underground radioactive waste repositories. Five research teams used different approaches to model stress/deformation, flow and transport processes, based on either discrete fracture network or equivalent continuum models. The simulation results derived by various teams generally demonstrated that rock stresses could significantly influence solute transport processes through stress-induced changes in fracture apertures and associated changes in permeability. Reasonably good agreement was achieved regarding advection and matrix diffusion given the same fracture network, while some observed discrepancies could be explained by different mechanical or transport modeling approaches.
|
|
| 26. |
- Zou, Liangchao, 1987-, et al.
(författare)
-
Analysis of Bingham fluid radial flow in smooth fractures
- 2020
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 12:5, s. 1112-1118
-
Tidskriftsartikel (refereegranskat)abstract
- Solutions for radial flow of a Bingham fluid are analyzed in this paper. It aims to eliminate confusions in the literature concerning the plug flow region in different solutions for analysis and design of grouting in rock fractures. The analyses based on the force balance equation reveal that the plug flow region in Bingham radial flow is independent of the fracture radius, and is not a growth function adapted from the solution of one-dimensional (1D) slit flow according to 'similarity'. Based on the shear stress distribution, we analytically proposed that a non-uniform plug flow region cannot exist. The Bingham fluid (grout) penetration and flowrate evolution as functions of grouting time are given using the correct expression for the plug flow region. The radius-independent plug flow region and the presented flowrate evolution equation are also verified numerically. For radial flow, the relative penetration length is equal to the relative width of plug flow region, which is the same as that for 1D channel flow. Discrepancies in analytical solutions for grout penetration and flowrate evolution were also illustrated. The clarification of the plug flow region and evaluation of discrepancies in analytical solutions presented in this work could simplify modeling and design of grouting in rock engineering applications.
|
|
| 27. |
- Zou, Liangchao, 1987-, et al.
(författare)
-
Impact of normal stress-induced closure on laboratory-scale solute transport in a natural rock fracture
- 2020
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Chinese Academy of Sciences. - 1674-7755.
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of normal stress-induced closure on fluid flow and solute transport in a single rock fracture is demonstrated in this study. The fracture is created from a measured surface of a granite rock sample. The Bandis model is used to calculate the fracture closure due to normal stress, and the fluid flow is simulated by solving the Reynold equation. The Lagrangian particle tracking method is applied to modeling the advective transport in the fracture. The results show that the normal stress significantly affects fluid flow and solute transport in rock fractures. It causes fracture closure and creates asperity contact areas, which significantly reduces the effective hydraulic aperture and enhances flow channeling. Consequently, the reduced aperture and enhanced channeling affect travel time distributions. In particular, the enhanced channeling results in enhanced first arriving and tailing behaviors for solute transport. The fracture normal stiffness correlates linearly with the 5th and 95th percentiles of the normalized travel time. The finding from this study may help to better understand the stress-dependent solute transport processes in natural rock fractures.
|
|
| 28. |
- Zou, Liangchao, 1987-, et al.
(författare)
-
Reply to Discussion on "Analysis of Bingham fluid radial flow in smooth fractures"
- 2021
-
Ingår i: Journal of Rock Mechanics and Geotechnical Engineering. - : Elsevier BV. - 1674-7755. ; 13:4, s. 945-946
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Recently, Hoang et al. (2021) discussed our paper Zou et al. (2020). In our paper, we made a statement that Dai and Bird (1981)'s solution for two-dimensional (2D) radial Bingham fluid flow between parallel plates violates mass balance. Hoang et al. pointed out that Dai and Bird (1981)'s solution does not violate the mass balance because Dai and Bird (1981)'s solution and our analysis are based on different assumptions, i.e. with consideration of the vertical velocity component in the continuity equation or not, which leads to two different approximation models. In this sense, the mass balance of Dai and Bird (1981)'s solution should not be checked using our solution as a reference. In this reply, we add remarks on the two approximation models and their implication for rock grouting analysis. The discussion by Hoang et al. and this reply are helpful to thoroughly eliminate the existing confusion regarding the two solutions in the rock grouting research community.
|
|
