During metal mining, the deformation and failure of rock mass are very important factors that dominate rock movement and zoning. Numerical modelling provides a feasible way to study the deformation ...and failure of rock mass. In this study, a numerical method of UDEC was adopted to study strata movement mechanism influenced by NWW-trending joints at the footwall at Chengchao Iron Mine, and the Mohr-Coulomb model and the Coulomb-slip model with residual strength were adopted as the constitutive models of rock masses and joints, respectively. The whole strata movement process was simulated and the strata movement mechanism at footwall and zoning phenomenon was clarified. In the chimney caving development stage, gravity is the driving force and surface deformations are mainly subsidence deformation of the surface above the ore body. In the post-chimney deformation stage, horizontal tectonic stress is the driving force and surface deformation and subsidence are dominated by horizontal deformation of the hanging wall and footwall in the mining area. After the level −395.0 m is mined out, the deformation characteristics of deep surrounding rock were revealed by means of numerical modelling, the maximum failure depth of the cantilever beam and the spatial distribution of deep surrounding rock zones can be determined. At last, the influencing boundary of surface deformation expands rapidly in a linear way with the excavation step and the expanding velocity of the horizontal deformation is greater than that of the subsidence in the post-chimney deformation stage.
This study investigates a complex slope failure that occurred in Chongqing Xi railway station. The studied slope belongs to a under-dip shale slope. Onsite surveys and UDEC numerical modelling were ...conducted to describe the deformation characteristics and potential failure mechanism of this slope. The simulated results suggest that sliding, buckling and toppling can occur in the deformation process, which is verified by the actual deformation characteristic of the slope and monitoring results. Moreover, the effects of bedding dip angle, slope angle, bed thickness on the deformation characteristics of the slope were also investigated with UDEC models. Finally, the possible slope structure for occurrence of slide-buckling-toppling failure and several numerically validated remedial measures were proposed.
Laboratory tests revealed that by enhancing the weathering degree, a transition of pre-peak stress-strain mechanical responses of crystalline rocks under unconfined compression from approximate ...linearity to nonlinearity was evident, as was the weakening of macro-mechanical properties. However, thus far, very few numerical studies have been conducted to quantitatively characterize the strong-to-weak transition of the mechanical behaviors of crystalline rocks modulated by the weathering degree. We propose an advanced grain-based model (AGBM) using Universal Distinct Element Code (UDEC) to characterize mechanical characteristics of crystalline rocks with different weathering degrees. The weathering-induced deterioration of microstructures was treated as loosening of grain contacts and weakening of their properties. It was proved that the grain contact model that considered hardening nonlinear deformation in compression and linearly elastic deformation in tension or shear was feasible and applicable to characterize the mechanical behaviors of crystalline rocks with different weathering degrees. The compression hardening deformation of grain contacts significantly affected the macro nonlinear stress-strain relation and stress thresholds of crack closure, crack imitation, stable crack growth, and unstable crack growth. We acquired new insights on the weathering-induced weakening of macro-mechanical characteristics of crystalline rock, which resulted from weakening of deformation properties of the grain contact more than grain contact strength.
•An AGBM was proposed to characterize strong-to-weak transition of mechanical behaviors of crystalline rocks with different weathering degrees.•Weathering-induced deterioration of microstructures was treated as loosening and property weakening of grain contacts.•Weakening of macro mechanical characteristics resulted from weakening of grain contact stiffness more than its strength.
Time-dependent deformation of brittle rock pillars is investigated using laboratory-scale pillar models using the grain-based time-to-failure model (GBM-TtoF). First, time-dependent deformations of ...rock pillars are analyzed and the results are compared qualitatively with field observations. Second, the influence of the boundary profile of pillar walls on time-dependent strength and deformation of rock pillars is investigated. Two factors, pillar shape and loading ratio, which influence the time-dependent strength and deformation of rock pillars, are studied by conducting a series of creep simulations using four pillar models with width to height ratios of W/H = 0.5, 1.0, 1.5 and 2.0. Finally, long-term strengths and deformation features of slender and squat pillars are analyzed. It is found that time-dependent strengths and deformation of rock pillars can be simulated using the GBM-TtoF creep model properly. Gradual spalling on the pillar walls can be captured using pillar models with rough boundary profiles. Creep deformations of slender and squat pillars could be quite different. Slender pillars are more likely to fail as time passes but squat pillars can tolerate more spalling on the walls without losing their stability. It is demonstrated that the GBM-TtoF creep model can simulate time-dependent strength and deformation of hard rock pillars well under creep loading conditions.
Instability and failure mechanism of coal wall at coalface is one of the hot-button and difficult issues in the study of coal mine ground control. Research to date has mainly focused on the ...macro-characteristics of coal face failure whereas few efforts have been devoted to the micro aspects or to the mechanisms behind these failures. The work described here takes coal face 8102 in the Wolonghu Mine, China, as an example and employs distinct element numerical software (UDEC) to investigate the distribution of abutment stress in front of the coal face at different mining dip angles from micro and macro perspectives, and reveal the main failure form and location of coal rib. The numerical results indicate the following six points. (1) The distance between the location of the peak abutment stress and the coal face increases with greater mining dip angles. (2) The rank by angle of abutment stress concentration factors is horizontal >up-dip> down-dip coal faces.(3) Tensile fractures dominate the failure of horizontal and up-dip coal faces and the only difference between the two is the form of the failure. (4) Shear fractures are the dominant failure components of down-dip coal faces. (5) The coal face failure forms include integral rib spall and a combination of upper-rib shear failure and roof caving. (6) Tensile fractures are mainly responsible for roof failures. The difference in roof movement between up-dip and down-dip coal faces is reflected in the forms of failure of their coal faces and of their roofs. Moreover, the effect of coalface depth, mining height, panel advance velocity and coal strength on the stability of coal rib is studied. The conclusions obtained from numerical simulation are consistent with engineering result, which verifies the reasonability of simulation analysis by UDEC. Finally, we propose measures to avoid coal face failure in the Wolonghu mine considering the numerical outcomes, the monitored strata behavior, and the recorded setting support resistance.
The Mohr-Coulomb (MC) shear strength parameters, cohesion c and angle of friction φ, are required in numerical models. Currently, the geological strength index (GSI) system has been widely used for ...estimating shear strength of blocky rock masses in rock engineering. However, the GSI system does not include the effect of joint orientation β on the mechanical properties of a rock mass, which means that the shear strength model cannot reflect anisotropic rock mass strength behavior caused by joint orientation. In this research, UDEC-based synthetic rock mass models, which are calibrated by experimental data, are adopted to study the effect of joint orientation on the shear strength of blocky rock masses with two perpendicular joint sets. The values of cohesion c and angle of friction φ estimated from the numerical simulation are compared with those calculated from the empirical shear strength models based on the GSI system. Comparison of the results shows that the existing empirical model overestimates the shear strength of rock mass when 10° <β < 45°, which may impose a risk on engineering design. To rectify the problem, based on the analysis of shear strength parameters of rock masses with various joint orientations, anisotropic weighting factors are proposed to modify the existing model. The proposed modified model is capable of providing conservative but more accurate estimation of the shear strength of rock mass, which is important for safe engineering designs.
Large deformations such as roof subsidence, floor heave, and two-sided deformations occur frequently in deep soft-rock roadways. The deformation becomes more severe under the combined effect of high ...in-situ and mining-induced stresses, which detrimentally affect the safe mining of coal. Based on the geological conditions and roadway failure characteristics of the Nanyaotou coal mine in Shanxi province, China, we used comprehensive numerical simulations and field observations to study roadway deformation and failure. The deformation mechanism of deep soft-rock roadways under dynamic pressures is described, and the corresponding control measures are proposed. The deformation and fracture development characteristics of roadways surrounding rocks were explored with a primary support scheme, and its effects were evaluated. The radius of the plastic zone and the displacement deformation of the roadway were studied by using theoretical analysis, and a combined-support design of “anchor bolt + anchor cable + shotcrete + deep and shallow borehole grouting + inverted arch” was proposed to limit deformations and relieve the stress in the surrounding rocks. Numerical simulations and field monitoring showed that the combined support scheme can effectively mitigate the large deformations of ventilation roadways and provide guidance for the stable control of deep soft-rock roadways.
Characterization on the response of the jointed rock mass to the stress wave is of great significance for rock engineering and the prevention of dynamic geological disasters. A joint in the rock mass ...produces discontinuous deformation under dynamic loads and can be weakened on both stiffness and strength, which further affect stress wave propagation in a feedback manner. However, previous numerical models mainly used the linearly elastic model (LEM) (constant stiffness) and the nonlinear Bandis-Barton model (BBM) (compression-strengthening stiffness) to characterize the dynamic response of the rock mass which neglected dynamic damage and stiffness weakening of the joint. To overcome this problem, we adopted a modified BBM (MBBM) to establish an advanced numerical model of the dynamic response of the rock mass by the Universal Distinct Element Code (UDEC). The MBBM is capable of characterizing joint stiffness weakening attributed to the filled particle crushing, which can be also degraded into both LEM and BBM. Our model was well verified by experimental data on stress wave propagation through an artificial filled joint. Dynamic responses of rock masses containing a single joint, a set of parallel joints, and intersected joints were systematically investigated considering the amplitude and incident angle of the incident wave as well as the joint spacing. Results showed that weakening of the joint stiffness had an important impact on the wave transmission and effect of multiple reflections at joints. Compared with previous models, our model has prominent advantages and accuracy in simulating dynamic damage and weakening response of the rock mass.
Highlights
A joint constitutive model considering stiffness weakening attribute to filled particle crushing was implemented in UDEC.
Dynamic damage of the filled joint and its effect on stress wave propagation was quantitively characterized.
Interaction between the stress wave and the rock mass with varied structures was systematically examined.
Gob-side entry retaining is a non-chain pillar mining technology in which reasonable roadside support is important for efficient roadway maintenance and goaf isolation in coal mines. A UDEC Trigon ...model is adopted in this paper to study the mechanism of crack expansion and evolution at various distances from the working face. This is done to optimize parameters for the roadside backfill body (RBB) by combining emergence, development and aggregation of micro-cracks with macroscopic mechanical responses. Results of the model show that cracks first appear in the top and bottom corner of the roadway in the lane-side RBB. Damage to the RBB is mainly caused by tensile cracks, which can be divided into main and secondary crack-development and yield-bearing zones. A reasonable aspect ratio of the RBB can greatly increase the area of the yield-bearing zone and reduce the damage degree, while reducing the number of penetrating cracks and preventing generation of seepage channels. The application of this model for gob-side entry retaining in the intake airway of the N2105 working face in the Yuwu coal mine indicates that deformation of the surrounding rocks can be effectively controlled.
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