FLAC3D Model Research Articles

New Numerical Technique for the Inbuilt Modified Cam Clay Constitutive Model in FLAC3D

Fast Lagrangian Analysis of Continua (FLAC) is a powerful numerical platform for simulating the deformation and stability of geotechnical structures. Presently, it is documented that the embedded Modified Cam Clay constitutive model in the FLAC platform is deficient in solving geotechnical problems. This paper outlines the new calibration approach by determining the isotropic preconsolidation pressure multiplier based on the relationship between the total stress in the geotechnical problem and the reference pressure. The multiplier was used to establish the nominated maximum isotopic preconsolidation pressure and maximum referential consolidation ratio at the bottom of the soil layer. Subsequently, the maximum isotopic preconsolidation pressure was used to determine the bulk maximum. In addition, the developed approach was used to investigate the lateral displacement of the large grid wall foundation by deep mixing under the adjacent surcharge loading. The feasibility was validated using the centrifuge results. The coefficient of determination between lateral displacement from numerical and centrifuge modelling R2 was 0.95. The proposed numerical technique and calibration approach demonstrated that the embedded Modified Cam Clay model can be used to solve practical geotechnical problems.

Numerical analysis of buried pipelines under seismic slope instability

Damage to buried pipes under seismic landslide actions has been reported in many post-earthquake reconnaissance. The landslide-pipe problem in the technical literature has been often investigated using simplified analytical methods. However, the analytical methods ignore the real mechanism of pipe response under natural dynamic slope instability. The dynamic slope instability is significantly influenced by its lateral boundary interface (LBI) characteristics. In this study, slope-pipe interaction (SPI) under seismic loading, focusing on the effect of LBI properties, is evaluated by continuum numerical simulation using the SANISAND constitutive model in FLAC3D. The results show that the geometry of the failure mass varies from 2D to 3D by increasing the stiffness at the slope boundaries (from smooth to hard) and the maximum pipe deformation decreases by around 40%. Moreover, the response components of maximum axial stress, bending moment, and shear stress of the pipe occur at the end sections of the buried pipe and near the boundaries of the landslide zone. However, the maximum pipe deflection occurs in the middle section of the pipe. The results of shear force-shear displacement curves demonstrate that the soil-pipe interaction stiffness is variable along the pipe length and can be estimated by a hyperbolic equation.

Evaluation of rock stability challenges affecting the formation of sustainable pit lake towards mine closure following crown pillar extraction in open pit-underground mines

The extraction of high-grade ore from the crown pillar (CP) in open pit-underground mines poses stability challenges and potential environmental risks. While an open pit has the potential to transition into a pit lake, the extraction of CP can induce failure in the surrounding walls, preventing the formation of the lake. There is also a concern that the backfilling material may not effectively confine toxic water within the pit, thereby risking contamination of the underground environment. To address these issues, a case study was conducted using FLAC3D and 3DEC models to evaluate the extent of failure caused by CP extraction. On-site observation, along with modelling, has revealed rock damage, including deformation stretching about 4 m from the pit wall and extending vertically from the pit floor to the ramp. The study identified three primary factors leading to pit wall failure or damage: steep pit slopes reaching approximately 70° near the pit floor, an underestimated CP thickness by about 4 m, and the concurrent extraction of ore from the pit wall alongside CP. Based on these findings, rehabilitation measures are suggested, including excavation of the deformed wall and cantilever, as well as partial pit backfilling. There is a substantial increase in the volume of backfill material as the extent of failure increases, which raise concerns about the decision-making process regarding CP extraction. Therefore, this article aims to raise environmental awareness and evaluate whether the benefits of ore extraction outweigh the considerations for pit wall support and the rehabilitation efforts during mine closure.

Application of an Integrated 3D–2D Modeling Approach for Pillar Support Design in a Western US Underground Coal Mine

Discontinuum Bonded Block Modeling (BBM) represents a potential tool for support design, as these models can reproduce both the rock fracturing process and the influence of reinforcement on unsupported ground. Despite their strengths, discontinuum models are seldom used for mining design due to their computationally intensive nature. This study is an application of an integrated 3D continuum–2D discontinuum approach, in which the mine-wide stress distribution process is modeled using a continuum software, and the local deformation behavior in response to a strain path from the continuum model is simulated with a 2D discontinuum software. In June 2017, two multi-point borehole extensometers were installed in a longwall chain pillar to record ground displacements as a function of the longwall face position. The data from one of the extensometers were employed to calibrate a panel-scale FLAC3D model. The boundary conditions along the pillar slice containing the extensometer were extracted from the FLAC3D model and applied to a 2D BBM, and the input parameters were modified to match the extensometer data. The calibrated BBM was able to reproduce the unsupported rib deformation and depth of the fracturing well. Subsequently, a few support schemes were tested to demonstrate how the incorporation of support might affect rib deformation.

Goaf risk prediction based on IAOA–SVM and numerical simulation: A case study

In regard to goaf risk prediction, due to the low accuracy and single prediction method, this study proposes a method that combines the improved arithmetic optimization algorithm (IAOA) – support vector machines (SVM) with GoCAD–FLAC3D numerical simulation. Thus, goaf risk is comprehensively predicted. From the perspectives of geological and engineering conditions, eight factors that affect goaf stability and 176 sets of sample data were determined. We utilized eight influencing factors such as rock mass structure, geological structure, and goaf burial depth as inputs, and the goaf risk level as the output. Moreover, an IAOA–SVM goaf risk prediction model was established. The 30 goaf areas of Yangla Copper Mine in Yunnan Province were selected as the research subject. First, the rationality of mechanical parameter values in the numerical model was verified using the parameter inversion method. Second, based on the GoCAD–FLAC3D numerical simulation method, the goaf risk analysis in Yangla Copper Mine was performed. Subsequently, using numerical simulation verification, the goaf filling effect was analyzed. Finally, the prediction results of the IAOA–SVM model were compared with that of other intelligent algorithms. The results indicate that the numerical simulation results of the GoCAD–FLAC3D model are consistent with those of IAOA–SVM and the actual results, which further verifies the effectiveness and superiority of the IAOA–SVM prediction model. Therefore, an innovative approach for goaf risk prediction is developed.

Investigating the Mechanical Responses and Construction Optimization for Shallow Super-Large Span Tunnels in Weathered Tuff Stratum Based on Field Monitoring and Flac3D Modeling

Investigating the Mechanical Responses and Construction Optimization for Shallow Super-Large Span Tunnels in Weathered Tuff Stratum Based on Field Monitoring and Flac3D Modeling

Research on Constitutive Model and Algorithm of High-Temperature-Load Coupling Damage Based on the Zienkiewicz–Pande Yield Criterion

The mechanical properties of rock can be weakened under the influence of high temperatures. To describe the mechanical behavior of rock under the action of high temperature more accurately, based on the Zienkiewicz–Pande yield criterion, the damage variable Dc which accounts for the coupling between high temperature and load is introduced. According to plastic potential theory and plastic flow law, the iterative incremental method for a high-temperature and load-coupled damage constitutive model in Flac3D is deduced in detail and compiled into the corresponding dynamic link library file (.dll file). By modifying the shape function to degenerate into the Mohr–Coulomb constitutive model, an elastic–plastic analysis of an ideal circular tunnel is performed, and a comparison is made between calculation results obtained from the built-in Mohr–Coulomb constitutive model in Flac3D, proving the correctness of the secondary development program. Finally, numerical simulations are conducted to study the effects of high-temperature damage using rock uniaxial compression tests, and the model’s validity is established by comparing it with previous experimental results.

TRANSITION FROM OPEN PIT COAL MINE TO THE UNDERGROUND MINE IN SOFT ROCKS

To achieve a successful and effective operation, the transition from open pit to underground mining requires accurate planning and analysis. Numerical modeling utilizing programs like FLAC3D has been an important tool for simulating and analyzing the complicated geomechanical behavior connected with this shift in recent years. The use of FLAC3D to develop a model for the switch from open pit coal mining to underground coal mining in soft rocks with using room and pillar mining method is explored in this abstract. It presents the development of model to analyze and simulate the complex dynamics of this transition. The significant considerations that went into developing the model, such as geotechnical characteristics, rock mass behavior, and mine design parameters, are highlighted in the abstract. It highlights how essential proper input data are to producing reliable simulations and forecasts in soft rocks. The usage of FLAC3D for tracking pit wall stability during the transition period, evaluating the influence on nearby infrastructure, and optimizing underground mine design are covered in the abstract. The models flexibility allows the investigation of various conditions and offers valuable insight about the transition process. The research emphasizes the potential of the FLAC3D model to lead decision-making during the transition from open pit to underground mining through detailed analysis like choosing appropriate width for main entrance and cross section stopes and their interpretation. It emphasizes how important it is to understand the geomechanical behavior of the coal deposit, optimize the mines design parameters, and ensure safety for employees. The room and pillar method is utilized to recover coal resources from deep underground mines, and the results from the model can help improve efficiency, sustainability, and risk prevention. KEYWORDS: Underground mining, Open pit mining, Room and Pillar mining method, FLAC3D, Coal mining, Soft rocks.

Design of an Anthracite Creep Model Based on Fractional Order Theory: Experiments and Simulations

Fractional order theory was used to characterize the accelerated creep phase of a nonlinear creep model. To accurately describe each stage of the anthracite creep model, the “gyroscope” unit was introduced by combining the Heaviside function and the creep damage definition. The effect of damage on anthracite creep was determined by designing and completing three-axis graded-separation loading creep tests on anthracite. The test curves were combined to classify anthracite into five stages: transient deformation, pseudo-acceleration, deceleration, isothermal, and acceleration creep. Each stage was combined with suitable components to form a combined fractional-order creep model. The one-dimensional equation of the state of the model was extended to three dimensions. The Levenberg–Marquardt optimization algorithm for fitting origin rheological curves was used to complete the fitting of the basic parameters. Finite differences were performed on the model equation of state, and a secondary development of a combined fractional-order creep model (NEG) was completed based on the built-in Burgers model in FLAC3D. A comparison of the numerical simulation results shows that the combined fractional-order creep model is important for accurately predicting the full creep stage of anthracite.

New method and application of disturbance range prediction for caving method of metal ore

AbstractTo quantify the disturbance range of the metal ore caving method, a new method to predict the disturbance range based on rock mechanics parameters is proposed. By combining the rock mechanics index with random medium theory, the prediction correction formula of the disturbance range is established. Based on disturbance equivalent centre and disturbance attenuation sphere, the two-dimensional safety criterion of mining disturbance in metal mines is derived. The new method is applied to 6 mines and the Jianshan Iron Mine, and the numerical simulation of the Jianshan Iron Mine by FLAC3D model is performed. The posteriori error ratio between predicted value and measured value is 0.0357, and the multi-factor cross analysis shows that the relative error of this method to the result is only 0.078. It is found that the method has high prediction accuracy and does not significantly affect the security.

A 3D torus-slice model for limit equilibrium analysis of shield tunnel face under soil arching effect

This paper proposes a torus-slice model to estimate the tunnel face critical support pressure, (σcrit) from the shield machine under the influence of soil arching. The failure envelope of the tunnel face is created by a cluster of discrete points using a spatial discretization technique. The vertical earth pressure loaded on the failure soil mass in front of the face is determined by an arching mechanism based on the rotation trajectory of the major principal stress. The tunnel face support pressure distribution is derived from the stress interaction using a stepwise method between the horizontal slices divided from the torus. The comparisons between the centrifuge tests and analytical solutions demonstrate the accuracy of the proposed model. The pressure distribution is further validated by the results of a FLAC3D model and analytical solutions. The failure envelope is compared to the geometry of the shear band from the numerical model, indicating the rationality of the proposed method. With an improved geometry considered, the proposed torus-slice model demonstrates the advantages over the classical silo-wedge model. Finally, the effects of material and geometrical parameters on a required tunnel face pressure are discussed. The results show that the soil internal friction angle φ’, cohesion c’, the soil-shield interface friction angle δ, and the geometric shape factor Tm all have significant effects on the tunnel face stability.

A novel long-short term memory network approach for stress model updating for excavations in high stress environments

ABSTRACT Digitalisation has increased access to large amounts of data for rock engineers. Machine learning presents an opportunity to aid data interpretation. The operators of Garson Mine use a microseismic database to calibrate a mine-scale finite difference model, used to assess seismic risk to inform mine operations. A Long-Short Term Memory (LSTM) network is proposed for stress model updating. The model is trained using microseismic data, geology, and geomechanical parameters from the FLAC3D model. Two LSTM networks are developed for Garson Mine: (1) predicting far field principal stresses in the FLAC3D model, and (2) predicting the far field six-component stress tensors in the model. Various LSTM network hyperparameters were analyzed to determine the architecture for the targets: input encoding and pre-processing, training solver, network layer architecture, and cost function. Architectures were chosen based on the corrected Akaike Information Criterion (AICc), coefficient of determination (R2), and percent capture (%C). When predicting principal stresses, AICc = −59.62, R2 = 0.996, and %C = 97%, and when predicting the six-component stress tensor AICc = −45.50, R2 = 0.997, and %C = 80%. This research represents progress towards continuous, automated updating of numerical models such that rapid, more accurate forecasts of changes in stress conditions will allow earlier reaction to challenging stress environments, increasing safety of excavations.

Analysis of the Influence of Oblique Shield Tunnel Construction on Existing Tunnels: A FLAC3D Modeling Approach

This study presents a comprehensive analysis of the influence parameters associated with the construction of a shield tunnel crossing an existing tunnel at an oblique angle. A three-dimensional model was developed using the finite difference software FLAC3D to simulate the construction process. The influence parameters, including geometric spatial position, shield construction parameters, and surrounding rock soil properties near the existing tunnel, were thoroughly examined. The degree of impact resulting from the oblique shield tunnel construction on existing tunnels was determined based on ground displacement, settlement of the existing tunnel, and changes in soil layers. The study summarizes the identified impact laws and investigates the interaction relationship between newly constructed shield tunnels, soil, and existing tunnels. The findings of this research provide a solid research foundation for ensuring the safety control of shield tunneling in proximity to existing tunnels.

Development of Transversely Isotropic Elastoplastic Constitutive Model in FLAC3D and Its Application in Tunnel Engineering

The obvious anisotropy of layered rock mass prevents the built-in constitutive model of commercial simulation software from accurately describing the elastoplastic behavior of the rock mass. In this paper, a transversely isotropic elastoplastic constitutive model (called the AN-MC model) that characterizes the elastoplastic failure behavior of the layered rock mass is developed by introducing the Mohr-Coulomb yield criterion with the tension cutoff in the model based on the transversely isotropic constitutive model and deriving its finite difference scheme. The development and programming of the transversely isotropic elastoplastic constitutive model are achieved on the basis of the secondary development platform of FLAC3D and the VC++ environment. The accuracy and rationality of the proposed constitutive model are verified in terms of consistency of the calculation results of the developed transversely isotropic elastoplastic constitutive model and the built-in constitutive models. In the numerical analysis of the Queerxi tunnel project, the calculation results of the AN-MC model are in good agreement with the field monitoring data. Thus, the deformation characteristics of the tunnel surrounding rock are well characterized. Comparative analysis of the deformation and failure laws of the layered surrounding rock and isotropic surrounding rock indicates that the plastic failure range of the layered surrounding rock tunnel is larger, and the arch foot and waist are prone to plastic penetration failure with butterfly-shaped characteristics. The research results are important for the scientific prediction and precise support of layered rock mass deformation.

Exploration of Limestone Pillar Stability in Multiple-Level Mining Conditions Using Numerical Models.

Pillar stability continues to be a significant concern in multiple-level mining conditions, particularly for deep mines when pillars are not stacked or the thickness of interburden between mining levels is thin. The National Institute for Occupational Safety and Health (NIOSH) is currently conducting research to investigate the stability of pillars in multiple-level limestone mines. In this study, FLAC3D models were created to investigate the effect of interburden thickness, the degree of pillar offset between mining levels, and in situ stress conditions on pillar stability at various depths of cover. The FLAC3D models were validated through in situ monitoring that was conducted at a multiple-level stone mine. The critical interburden thickness required to minimize the interaction between the mining levels on top-level pillar stability was explored, where the top level mine was developed first followed by the bottom level mine. The model results showed that there is an interaction between numerous factors that control the stability of pillars in multiple-level conditions. A combination of these factors may lead to various degrees of pillar instabilities. The highest degree of local pillar instability occurred when pillar overlap ranges between 10 and 70%. On the contrary, the highest degree of stability occurs when the pillars are stacked, the underlying assumption is that the interburden between mining levels is elastic (never fails). Generally, for depths of cover investigated in this study, the stability of top-level pillars shallower than 100 m (328 ft) or with interburden thicknesses greater than 1.33 times the roof span-16 m (52.4 ft) in this study-does not appear significantly impacted by pillar offset. The results of this study improve understanding of multiple-level interactions and advances the ultimate goal of reducing the risk of pillar instability in underground stone mines.

Numerical Study of the Effect of Grout Material Properties on Ground Deformation during Shallow TBM Tunneling

The full-face shield tunnel boring machine (TBM) has been widely used to build tunnels in urban area. Ground deformations usually occur during tunnelling processes, which is closely related to engineering geological property. A large ground deformation may lead to large-scale surface settlement or ground collapse, especially for shallow buried tunnels. In general, synchronous grouting is adopted to reduce the ground deformation. The temporal and spatial distribution of the grout pressure and consolidation processes of grouting have a significant influence on the deformation. For a better understanding the relationship between the grout material type and the ground deformation, the present study models a complex numerical model in FLAC3D based on the Guangzhou Metro line 18. A numerical method is proposed to reproduce the tunnelling process and the consolidation process of grout material. The effect of grouting material on ground deformation is discussed, i.e., immediately solidified type, quick hardening type, and good mobility type. The ground deformation of the numerical simulation are compared to those monitored in the field. The results indicate that the immediately solidified type grout can reduce the ground settlement effectively and is mainly applicable to secondary grouting. The quick hardening type can make the ground upheaval, which is smaller than that induced by immediately solidified type. The good mobility type can reduce the ground settlement and well control the ground deformation. The good mobility type recommends using in the numerical study for simulating the synchronous grouting.

Implementation of the Non-Associated Elastoplastic MSDPu Model in FLAC3D and Application for Stress Analysis of Backfilled Stopes

The multiaxial Mises-Schleicher and Drucker-Prager unified (MSDPu) criterion has been shown to exhibit several specific features compared to other yield and failure criteria, including a nonlinear mean stress dependency, influence of the Lode angle, use of independent uniaxial compressive and tensile strength values and absence of an apex (singularity) on the envelope surface in the negative stress quadrant. However, MSDPu has been seldom used in practice to solve geotechnical and geomechanical engineering problems mainly because it had not yet been fully implemented into three-dimensional (3D) numerical codes. To fill this gap, a 3D elastoplastic MSDPu formulation is developed and implemented into FLAC3D. The proposed MSDPu elastic-perfectly plastic (EPP) constitutive model is then validated against existing analytical solutions developed for calculating the stress and displacement distributions around cylindrical openings. The FLAC3D MSDPu-EPP model is then applied to evaluate the vertical and horizontal stress distributions in a three-dimensional vertical backfilled stope. The numerical results obtained with the MSDPu-EPP model are compared with those obtained with the Mohr-Coulomb EPP model, to highlight key features of the new formulation.

Analysis of Influence Factors of Negative Skin Friction on PHC Pile in High-Backfill Sites

It is recognized that NSF on a pile affects the structural and geotechnical design. The formation of NSF on a pre-stressed high-strength concrete (PHC) pile under a control building in a Vietnamese project was investigated using a verified numerical model in FLAC3D. The height of backfills, the consolidation degree of soil, working loads on the PHC pile, and the pile diameter were analyzed in sensitivity analyses to investigate the influence on NSF. It was found that higher backfills and higher consolidation degree were dominant in the formation of NSF, causing an increase of the dragload and an upward movement of the neutral plane. The working load and the pile diameter affected the dragload and the position of the neutral plane less. A limit decrease of the dragload induced by NSF was observed when the working load increased. Accelerating the soil consolidation process would be suggested to avoid great displacement due to NSF.

Numerical Investigation of Roof Stability in Longwall Face Developed in Shallow Depth under Weak Geological Conditions

Developing longwall mining under weak geological conditions imposes a substantial challenge with regard to the higher risk of falling roofs. Maintaining the stability of the longwall face in this aforementioned condition is crucial for smooth operation. Investigating roof conditions in longwall requires detailed study of rock behavior in response to a few key influences. This paper presents the outcome of a numerical analysis of roof stability in shallow depth longwall face under weak geological conditions. A series of validated FLAC3D models was developed to examine the roof condition of the longwall face under the influence of shield canopy ratio, shield resistance force, and stress ratio. The results show that these three key factors have a significant impact on longwall roof conditions, which can be used to optimize its stability. Two distinct mechanisms of the roof caving behavior can be observed under the influence of stress ratio. The countermeasures of reducing face-to-tip distance and cutting width are proposed to improve the roof condition of longwall face under weak rock. The outcomes show a substantial improvement in roof conditions after adopting the proposed method.

Improving the Numerical Modelling of In-Situ Rock Bolts Using Axial and Bending Strain Data from Instrumented Bolts

Numerical modelling has become an important tool in the underground rock bolt reinforcement designing process. Numerical modelling provides the advantage of easily and quickly simulating complex underground geometries and mechanisms with sensitivity analyses. However, a numerical model needs to be calibrated using mathematical solutions, lab testing or with actual in-situ observations and measurements (which is the preferred method) before its results can be quantitatively applied to reinforcement design. Instrumented rock bolts provide a useful data source for calibrating in-situ rock bolt models. In this work, procedures have been presented to identify and determine the orientation of structures in the rock mass based on the strains on the instrumented rock bolts. A method to calibrate the rock bolt model with in-situ data is also presented. The results of the presented procedures have been validated with laboratory tests and numerical modelling. The procedures have been applied to create and calibrate an in-situ rock bolt model in FLAC3D and the results are validated using in-situ data.