A grain‐based Universal Distinct Element Code model was developed to generate a deformable polygonal grain‐like structure to simulate the microstructure of brittle rock. It takes into account ...grain‐scale heterogeneity including microgeometric heterogeneity, grain‐scale elastic heterogeneity, and microcontact heterogeneity. The microgeometric heterogeneity can be used to match the grain size distribution of the rock. The discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy. The modeling approach was evaluated using Lac du Bonnet granite and Äspö Diorite. The microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading. The crack‐initiation stress was found to be controlled primarily by the microscale geometric heterogeneity, while the microcontact heterogeneity controlled the strength characteristics. The effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined.
Large deformation of soft rock roadway has always been a major difficulty in deep mining practices. This paper describes a case study of the failure mechanisms and stability control technology of ...deep roadway with soft rock mass in Xin'an coal mine in Gansu Province, China. Rock mass properties around the roadway are evaluated using geological strength index (GSI) based on the field data and the mechanical properties of intact rock specimens. The Universal Discrete Element Code (UDEC) software program is adopted to establish the numerical model of a ventilation roadway in Xin'an coal mine, and the micro-parameter calibration is conducted with the rock mass properties. The failure process of roadway under unsupported and primary support conditions is simulated; the deformation, stress and crack evolution characteristics were clearly illustrated. Failure first appears around the roadway surface because there is a high stress concentration around the roadway surface after excavation; the failure area propagates further into the deep surrounding rock as the stresses applied on the surface gradually decreases, finally resulting in a large zone of stress relaxation. There exists a large scale of tensile failure in the shallow rock, which leads to swelling and fracturing around the roadway. The primary support is low in strength with no support in the floor, which results in serious floor heave, side shrinking and roof subsidence. A new “bolt-cable-mesh-shotcrete+shell” combined support is proposed to support the ventilation roadway. The monitoring data in the experiment section show that the new support design successfully controls the large deformation of the roadway, which can provide helpful references for support designing of engineering in deep soft rock roadway.
•Evaluate rock mass properties around the roadway using GSI.•Establish the numerical model of a ventilation roadway in Xin'an coal mine using UDEC.•Obtain the deformation and stress behavior of roadway under various support conditions.•Analyze the crack evolution process of roadway under various support conditions.•Propose and validate a new “bolt-cable-mesh-shotcrete+shell” combined support mode.
A numerical simulator entitled TOUGH-UDEC is introduced for the analysis of coupled thermal-hydraulic-mechanical processes in fractured porous media. Two existing well-established codes, TOUGH2 and ...UDEC, are coupled to model multiphase fluid flows, heat transfers, and discontinuous deformations in fractured porous media by means of discrete fracture representation. TOUGH2 is widely used for the modeling of heat transfers and multiphase multicomponent fluid flows, and UDEC is a well-known distinct element code for rock mechanics. The two codes are solved sequentially, with coupling parameters passed to each equation at specific intervals. After solving thermal-hydraulic equations within the TOUGH2 code, pressure and temperature information is imported into the UDEC model. After solving the mechanical equation within the UDEC code the calculated fracture apertures are converted to the equivalent permeability and porosity values for a TOUGH2 flow analysis. The solution is calculated by iteratively following an explicit sequence for numerical efficiency. Verifications are presented to demonstrate the capabilities of the coupled TOUGH-UDEC simulator. Three application examples of (1) shear dilation due to increased pore pressure, (2) thermal stress and (3) CO2 injection, show that the new simulator can be an effective tool for geoengineering applications involving shear activation of fractures and faults.
•TOUGH2 and UDEC are linked to model coupled THM processes in fractured porous rock.•TOUGH-UDEC is verified by hydromechanical and thermomechanical verification cases.•TOUGH-UDEC is applied to two basic hydroshearing and thermoshearing models.•TOUGH-UDEC is applied to a large-scale CO2 injection and leakage analysis.
Flexural toppling failure (FTF) is one of the main types of toppling failures and frequently occurs in anti-inclined rock slopes. A new UDEC Trigon approach for simulating FTF of a model slope was ...presented in this paper. FTF of anti-inclined rock slopes characterized by tensile failure of rock columns was successfully captured with the new method. Subsequently, special effort was made to investigate the effects of joint cohesion and joint friction angle on flexural toppling movements' mechanisms. Furthermore, a limit equilibrium method, which can reflect the effects of the joint cohesion, was proposed to quantitatively evaluate the stability of anti-inclined rock slopes against FTF. The results demonstrate that the deformation process of FTF can be divided into three stages: elastic deformation due to cohesion, development of FTF after interlayer slip, and formation of the total failure surface. The inter-column normal forces will suddenly decrease when the failure surface begins to initiate inside the slope, which can be regarded as an instability indicator of anti-inclined rock slopes against FTF. Joint cohesion and joint friction angle were found to have significant effects on the stability of anti-inclined rock slopes, but make an insignificant impact on the shape, location, and formation process of the failure surface. The simulated results indicate that joint cohesion should be considered when using the limit equilibrium method to evaluate the stability of anti-inclined rock slopes against FTF. Inaccurate result will be predicted if the joint cohesion is neglected in the limit equilibrium method.
•Flexural toppling of rock slopes was accurately simulated using UDEC Trigon model.•Inter-column force during flexural toppling was studied.•Effects of joint cohesion and friction angle on flexural toppling were discussed.•A theoretical method including joint cohesion for flexural toppling was developed.
•The effect of cutting angles on RBB was discussed under static and dynamic loading.•Static loading is a bigger contributor to the failure compared to dynamic loading.•A combined support measure is ...proposed.
The applications of gob-side entry retaining (GER) techniques tends to increase over time as it can increase the minerals recovery rate and reduce the output of the waste. In the literature, only the performance of the roadside backfill body (RBB) at gob-side entry retaining under static loading has been investigated. However, failure mechanisms of the RBB under dynamic loading with various roof cutting angles have not been addressed. This study presented an numerical simulation of the fracture propagation and distribution in the roadside backfill body along the gob-side under combined static and dynamic loadings using the Trigon model built in UDEC (Discrete element methods) software. The influence of the roof cutting angles on the behavior of the RBB was also discussed. The input parameters were determined by back analysis with the field data. Results of the model show that static loading is a bigger contributor to the failure of the RBB compared to the dynamic loading. Several clear fractures were observed at top left and bottom right of the RBB and the fracture was more intensive at top left. In addition, it was found that if the roof cutting angle is 70°, the influence of the dynamic loading on the RBB is minimum, and the area and severity of the shearing failure in the RBB is minimum as well. As a result, it was determined the optimal roof cutting angle was 70° and a combined support measure of “roof cutting + roof support above RBBs + RBB reinforcement” is proposed. The application of roof cutting in gob-side entry retaining (RCGER) techniques in the Lingzhida coal mine indicates that deformation of the surrounding rocks can be effectively controlled.
Reservoir-induced earthquakes (RIEs) occur frequently in the Three Gorges Reservoir Area (TGRA) and the rock mass strength of the hydro-fluctuation belt (HFB) deteriorates severely due to the ...reservoir-induced seismic loads. Three models of typical bedded rock slopes (BRSs), i.e. gently (GIS), moderately (MIS), and steeply (SIS) inclined slopes, were proposed according to field investigations. The dynamic response mechanism and stability of the BRSs, affected by the rock mass deterioration of the HFB, were investigated by the shaking table test and the universal distinct element code (UDEC) simulation. Specifically, the amplification coefficient of the peak ground acceleration (PGA) of the slope was gradually attenuated under multiple seismic loads, and the acceleration response showed obvious “surface effect” and “elevation effect” in the horizontal and vertical directions, respectively. The “S-type” cubic function and “steep-rise type” exponential function were used to characterize the cumulative damage evolution of the slope caused by microseismic waves (low seismic waves) and high seismic waves, respectively. According to the dynamic responses of the acceleration, cumulative displacement, rock pressure, pore water pressure, damping ratio, natural frequency, stability coefficient, and sliding velocity of the slope, the typical evolution processes of the dynamic cumulative damage and instability failure of the slope were generalized, and the numerical and experimental results were compared. Considering the dynamic effects of the slope height (SH), slope angle (SA), bedding plane thickness (BPT), dip angle of the bedding plane (DABP), dynamic load amplitude (DLA), dynamic load frequency (DLF), height of water level of the hydro-fluctuation belt (HWLHFB), degradation range of the hydro-fluctuation belt (DRHFB), and degradation shape of the hydro-fluctuation belt (DSHFB), the sensitivity of factors influencing the slope dynamic stability using the orthogonal analysis method (OAM) was DLA > DRHFB > SA > SH > DLF > HWLHFB > DSHFB > DABP > BPT.
•Deterioration of the hydro-fluctuation belt in typical bank slope was considered.•Response rules of the dynamic characteristic parameters were analyzed.•Mathematical model of the nonlinear dynamic damage of slope was established.•Dynamic mechanism of the cumulative damage and instability of slope was revealed.•Sensitivity of factors affecting the dynamic stability of slope was discussed.
Abstract Rock anchors, which can withstand substantial forces and are essential for securing the foundations of the built environment, can fail due to steel tensile failure, bond detachment, or rock ...mass fracturing through uplift. In this study, uplift failure of the rock mass surrounding rock anchors was simulated using both physical and numerical models. The physical models used a specially designed testing rig with predefined sizes and different joint layouts to simulate rock mass uplift failure. The numerical models were calibrated using the physical models and used to investigate scenarios involving increased complexity and greater depths. This paper presents the load distribution within rock masses with orthogonal joints when exposed to an anchor load. Extensive analysis of the numerical models revealed that symmetrical load arches were induced in rock masses that contained a joint set oriented parallel to the loading direction. However, joints that were obliquely oriented relative to the anchor axis induced asymmetrical load arching. The greatest displacement occurred in the direction parallel to the joint set with the smallest angle to the anchor loading axis. Large-scale models with zero or near-zero in situ horizontal stress revealed that the load capacity in a rock mass with continuous vertical joints was relatively low, especially when compared to rock masses with discontinuous vertical joints. It was observed that the uplift capacity of the rock mass around an anchor decreased if the load arches of adjacent anchors overlapped; consequently, a decrease in anchor spacing was found to correspond to a decrease in uplift capacity.
Block identification serves as a critical preprocessing step in rock block system mechanical analysis. Presently, research primarily focuses on refining identification algorithms to accommodate ...increasingly complex joint models or enhance computational efficiency, while overlooking the influence of the block system expression derived from identification on subsequent mechanical analysis. Specifically, the precise role of small blocks within a block system during numerical simulation remains uncertain. Consequently, this paper developed a novel two-dimensional block identification method integrating small block treatment. The essence of this treatment lies in eliminating the short edges shared between small blocks and their adjacent blocks. Here we find that small block treatment is crucial for enhancing the efficiency and convergence of mechanical simulation. Through comparisons with the existing treatment methods using three cases in the Universal Distinct Element Code (UDEC), our method demonstrates superior computational efficiency and exhibits the best consistency with the results of the original models in Cases 1 and 2. Moreover, our method is uniquely capable of successfully conducting numerical simulations for Case 3. We anticipate our study to be a starting point for advancing the geometric optimization of block systems and bridging geometric and mechanical analyses in the realm of rock block mechanics analysis.
This paper presents the application of the hybrid continuum-discrete element method, i.e. Universal Distinct Element Code (UDEC), to simulate soil desiccation shrinkage and cracking. Herein, soil is ...modelled using a mix-mode cohesive fracture model that combines tension, compression and shear material behaviour. The fracture model considers both elastic and inelastic (decomposed to fracture and plastic) displacement, with the norm of the effective inelastic displacement being used to control the fracture behaviour. The applicability and capability of the proposed approach is demonstrated through numerical simulations of laboratory linearly-constrained desiccation test. Good agreements with the laboratory observations have been obtained. The dominant influencing factors on soil desiccation cracking have been assessed, several factors including shear strength and tensile strength of soil-base, and soil sample thickness were identified to have a significant controlling influence on desiccation cracking.
•A mixed-mode cohesive fracture model for laboratory soil desiccation simulation•Correlate the micro-parameter to macro-parameter•Investigate the desiccation cracking influential factors•The cohesive fracture model has potential application to field soil desiccation.
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