FLAC3D Software Research Articles

Numerical Simulation Research on Distribution Characteristics of Overlying Rock Stress Field in Floor Roadway

In order to explore the distribution characteristics of the overlying rock stress field in the floor roadway at different locations, FLAC3D software was used to simulate and analyze the surrounding rock directly above the floor roadway and the surrounding rock within 15m on both sides of the floor roadway when the distance between the floor roadway and the coal roadway and the horizontal distance were changed. The stress field distribution characteristics are obtained, and the stress field distribution characteristics of different areas directly above and on both sides of the floor roadway are obtained, which provides a theoretical basis for the location selection and support of the floor roadway.

The Formation Mechanism of Surface Landslide Disasters in the Mining Area under Different Slope Angles

Slope stability analysis is important for the safe mining of mineral resources. The collapse of goafs in loess gullies can lead to natural disasters such as surface landslides. In this context, this study analyzes monitoring data obtained from surface observation in the Shendong mining area of the Hanjiawan coal mine based on the geological conditions therein. The monitoring results show that the working face experiences a starting period, an active period, and a declining period, from the start of mining to the end of the working face. At the initial mining stage, there is no evident surface movement or deformation in the mining area. When the advance distance of the 12106 working face is between 13 m and 109 m, the surface movement and deformation vary significantly, and the maximum subsidence reaches 1963 mm, which is enough to cause landslides. We select the physical and mechanical parameters of the rock and soil in the mine and then simulate the formation mechanism of surface landslides under different slope angles of the mining area using FLAC3D software. Because of the collapse of the mined‐out area, the overlying strata structure is destroyed, the subsidence basin is shifted to the center as a whole, and the slope mass is subjected to tensile and compression deformation, resulting in plastic damage, which develops downward along the crack and leads to a collapse because of the discontinuous movement and deformation of the surface; moreover, step‐type ground fissures are produced. The results also show that when the slope angle is greater than 60°, the displacement of the slope mass is not uniform, and the rock stratum in a position with large displacement loses its support, leading to landslides; when the slope angle is less than 30°, the bedrock surface forms a sliding surface and develops to the surface, thus decreasing the possibility of landslides. Based on the stability analysis of the collapsed slope in the goaf of the loess gully, a scientific basis is provided for the effective prevention and control of geological disasters in the Shendong mining area.

Study on Optimization of Deep Foundation Pit Support Scheme under the Influence of Traffic Dynamic Load in the Reconstruction and Expansion of Jiqing Expressway

In this paper, based on the deep foundation pit support of the reconstruction and expansion project of Jiqing expressway, the FLAC3D software is used to establish the numerical calculation model of the deformation support of deep foundation pit under the influence of traffic dynamic load. The numerical calculation results are consistent with the actual project monitoring results. By changing the key support parameters such as pile diameter and pile distance, pile length, the level of piles under different support schemes is analyzed. The results show that the ideal diameter of bored pile is 0.8-1.2m, the spacing is 1.1-1.3m, the length of pile is 23m-28m. The horizontal displacement of pile body and ground settlement decrease with the increase of length and diameter of support pile. Considering the safety of foundation pit and the reduction of project cost, the pile with length 23m and diameter 0.8m is chosen in the practical engineering.

Long-term behavior of earth pressure around a high-filled cut-and-cover tunnel

The Northwest Loess Plateau in China is mountainous and contains deep valleys which consist mostly of loess. Tunnels constructed in such deep valley and backfilled with soil are called high-filled cut-and-cover tunnels (HFCCT). Several studies have been conducted on HFCCT, but the creep behavior of loess backfill has not been fully explored. Post-construction settlement in loess is large, and it is difficult for stability to be reached in a short time. Therefore, it is necessary to predict long-term behavior of earth pressure around an HFCCT to ensure long-term safety. The primary purpose of this paper is to investigate changes in earth pressure and displacement of soil with time after the completion of the backfill process. This is achieved using FLAC3D software (finite difference method). The results show that discrepancies in soil settlement and surface settlement will gradually increase and eventually reach stability. The distribution and value of earth pressure also becomes redistributed. Meanwhile, influencing factors such as slope angle and valley width gradually weaken with time, and only affect the time needed to reach stability.

Bearing Characteristics of Surrounding Rock of Deep Mining Roadway with Full and End Bolt Anchorages: A Comparative Numerical and Experimental Study

The support strength of surrounding rock in deep mining roadways can be significantly improved by replacing the end bolt anchorage with a full one. The support effects of both types of anchorage and the axial stress distribution characteristics in anchored bolt bodies were assessed via the indoor pull‐out test, simulated via the FLAC3D software, and verified by field measurements. The stability and variation patterns of the axial force, as well as the evolution law of bearing characteristics of surrounding rock, were analyzed. The results indicate that the polymorphic deformations of deep mining roadway surrounding rock and the bolt support body interact synchronously. The axial force evolution trend in bolt bodies with end anchorage revealed by field tests was consistent with the laboratory test results, in contrast to that of full anchorage. Although stress distribution laws in both sides of the mining roadway were the same for both types of anchorage, the vertical stress peak and damage range of full‐anchored surrounding rock slightly exceeded those of the end‐anchored one. The anchored area bearing a higher load alleviated the stress concentration of the surrounding rock. Since the deformations in fully and end anchored surrounding rocks increased gradually and sharply, respectively, the full anchorage is more conducive to deformation moving control of deep mining roadway surrounding rock. The research results can provide theoretical guidance for the design and construction of deep mining roadway bolt support.

Study on Dynamic Response Characteristics of Rock Slope

After the wenchuan earthquake, the dynamic response law of rock slope under the action of dynamic load is a very concerned and urgent problem in the field of seismic engineering. This paper analyzed the dynamic response law of simplified rock slope under the cosine wave dynamic load by numerical simulation with FLAC3D software. This research emphatically analyzed the variation law of amplification coefficient of seismic displacement, acceleration and velocity of rock slope under the condition of different slope height, slope angle, dynamic load period and dynamic load amplitude, which provides a basis for reducing seismic damage of slope area and seismic design of engineering structure.

Numerical Simulation of Surface Movement and Deformation Caused by Underground Mining with Complex Stratigraphic Boundary

The interface program of finite element software based on surface spline interpolation is developed by using MATLAB software. The controllable 3D surface modeling based on CAD contour is realized. Taking a mine as an example, the method of establishing the 3D numerical calculation model including complex stratum boundary is studied. The influence of underground mining on surface movement and deformation under complex stratum conditions by using the FLAC3D software further was discussed. The research results show that the developed interface program of finite element software can well realize the numerical modeling of complex formation and provide help for subsequent numerical simulation. The calculated subsidence value is in good agreement with the measured value. The values of surface tilt, surface curvature, and surface horizontal deformation are less than the relevant regulations. The mining method of the filling method has no obvious effect on the surface structures. The research results can provide reference for similar numerical simulation.

The Stability Study and Simulation of Soil Landslide Based on Bishop Method

Landslide is one of the most common disasters in nature and is a kind of slope failure. Many countries in the world suffered, because of its wide distribution, frequent occurrence and great harm. In China, the national economy and people’s lives and property suffer heavy losses due to the landslide disaster. In this paper, first of all, we used the Bishop method to theoretically analyze the stability of a landslide in Sichuan Province, and then we established a simulation model in Flac3D, the rock and soil mechanics calculation software developed by ITASCA company in the United States, to analyze the stability of the landslide under complex conditions. Finally, the results of theoretical analysis and simulation are consistent, which can provide ideas and methods for geological disaster prevention in the future.

Three dimensional seismic deformation-shear strain-swelling performance of America-California Oroville Earth-Fill Dam

Structural design of the vertical displacements and shear strains in the earth fill (EF) dams has great importance in the structural engineering problems. Moreover, far fault earthquakes have significant seismic effects on seismic damage performance of EF dams like the near fault earthquakes. For this reason, three dimensional (3D) earthquake damage performance of Oroville dam is assessed considering different far-fault ground motions in this study. Oroville Dam was built in United States of America-California and its height is 234.7 m (770 ft.). 3D model of Oroville dam is modelled using FLAC3D software based on finite difference approach. In order to represent interaction condition between discrete surfaces, special interface elements are used between dam body and foundation. Non-reflecting seismic boundary conditions (free field and quiet) are defined to the main surfaces of the dam for the nonlinear seismic analyses. 6 different far-fault ground motions are taken into account for the full reservoir condition of Oroville dam. According to nonlinear seismic analysis results, the effects of far-fault ground motions on the nonlinear seismic settlement and shear strain behaviour of Oroville EF dam are determined and evaluated in detail. It is clearly seen that far-fault earthquakes have very significant seismic effects on the settlement-shear strain behaviour of EF dams and these earthquakes create vital important seismic damages on the swelling behaviour of dam body surface. Moreover, it is proposed that far-fault ground motions should not be ignored while modelling EF dams.

Study on The Evaluation of Surrounding Rock Stability and Limit Displacement of High-Pressure Stratum Tunnel

Aiming at the problem of the value of the stability and limit displacement of the surrounding rock of highway tunnel with high pressure, the method of numerical limit analysis is adopted, and one of the working conditions is analyzed in detail. Firstly, this paper adopts the formation structure method to calculate and establish a plane model for calculation and analysis with the help of FLAC3D software, so as to study the influence of reduction coefficient on surrounding rock deformation and its law. Secondly, by holding other variables unchanged, two different working conditions with and without high water pressure are compared and analyzed, and it is obtained that the ultimate safety factor of the integrity instability of surrounding rock of the formation tunnel with high water pressure is 1.30, and that of the integrity instability of surrounding rock of the formation tunnel without high water pressure is 1.80. Finally, the results are compared and analyzed and it is found that the stability of tunnel surrounding rocks with high pressure is lower than that without high pressure, and the limit displacement is greater than that without high pressure.

Study on the Reinforcement Mechanism of the Deep Replacement Caverns for the Giant Slope Block Combined by Structural Planes

The left bank of the cushion pond of Baihetan hydropower station is a slant and dip slope. The gently inclined intra-layer fault zones, the steep-dip faults and the unloading fissures cutting the slope to form several potentially unstable blocks. The computational results show that the stabilities of the blocks are controlled by inclined intra-layer fault zones. A method of treatment applying deep replacement caverns and load-reduction excavation was proposed to reinforce the unstable blocks. In order to study the reinforcement mechanism of the deep replacement caverns for the giant slope blocks controlled by inclined intra-layer fault zones, the 3D simulation analysis of the slope treatment construction was carried out by use of FLAC3D software, and a 3D geo-mechanical model was developed to carry out experimental research. The results of the calculation and experiment show that the deep concrete replacement caverns effectively control the shear and sliding deformation of the bottom slide surface and improve the stability of the blocks combined by structural surfaces. In the process of slope strength reduction and overloading, the slope deformation and cracking are gradually extended from the surface to the inner part, and shear stresses of the front deep replacement cavern are the largest of all the caverns. Therefore, it is more beneficial to control the deformation of the slope and improve the stability of the giant blocks by increasing the size of the front deep replacement cavern. The research results have important guiding significance for the reinforcement treatment of the giant blocks in the left bank of Baihetan cushion pond and similar projects.

Study on Stability of Surrounding Rock of Mechanized Construction in Tunnel Entrance Section

With the development of tunnel construction technology and mechanical equipment, the mechanized drilling and blasting construction of mountain tunnels has gradually developed, but there are still certain problems in the mechanized tunnel entry. Relying on a tunnel project in Yunnan, this article uses FLAC3D software to study the stability of surrounding rock under the condition of mechanized large-section construction of shallow buried section of the tunnel entrance. When the shallow buried section of the cave entrance is constructed by the micro-step method, the surrounding rock displacement and plastic zone changes of the surrounding rock before and after the use of different cyclic footage and the tunnel face reinforcement when the tunnel face is used are compared and analyzed. The results of the study show that when the tunnel face is not reinforced, in order to ensure the safety of construction, the mechanized excavation cycle footage of the tunnel entrance section should be controlled within 1.2m, and the overlap length of the leading pipe shed should be greater than 5m; if the circulation is to be increased for footage, the tunnel face must be reinforced. Under the condition that the tunnel face is reinforced with glass fiber anchors with a length of 10m and a pitch of 1.5m, the cycle footage can be increased to 1.8m at most.

Numerical investigation of geocell reinforced slopes behaviorby considering geocell geometry effect

The present study evaluates geocell reinforced slope behavior. A three dimensional analysis is carried out to simulate soil and geocell elastoplastic behavior using the finite difference software FLAC3D. In order to investigate the geocell reinforcement effect, the geocell aperture size, thickness, geocell placement condition and soil compaction had been considered as variable parameters. Moreover, a comparison is evaluated between geocell reinforcing system and conventional planar reinforcement. The obtained results showed that the pocket size, thickness and soil compaction have considerable influence on the geocell reinforcement slope performance. Moreover, it was found that the critical sliding surface was bounded by the first geocell reinforcement and the slope stability increases, by increasing the vertical space between geocell layers. In addition, the comparison between geocell and geogrid reinforcement indicates the efficiency of using cellular honeycomb geosynthetic reinforcement.

Rational size and stability analysis of horizontal isolated pillars in deep mining from caving to filling method

For mining using the caving and filling methods in metal mines, determining a suitable size for the isolated pillars—the connecting part of the extension from shallow to deep—is crucial for ensuring safety and efficiency. Considering actual cases involving deep caving and cut-and-fill mining in the Chifeng Hongling lead-zinc mine in Inner Mongolia, China, the reserved thickness range of the horizontal isolation layer is obtained via theoretical analysis. On this basis, the pre-processing software HyperMesh is used to build a high-precision hexahedral grid model of the mining area, and the three-dimensional geological model of the mining area is imported into the finite-difference software FLAC3D. The stress field, displacement field, and plastic area evolution law of pillars (horizontally isolated pillars and adjacent rib pillars) in the stope of the ninth middle section after excavation are analyzed via numerical simulation inversion of the selected scheme of horizontal isolated pillars. The numerical simulation results show that the scheme employed to retain the upper horizontal isolated pillars in the ninth middle section involves reserving thicknesses of 8 m and 32 m at average ore body thicknesses of 15 m and 35 m, respectively. These results can provide theoretical guidance and a basis for safe and efficient mining of deep metal mines.

Finite element implementation of coupled hydro-mechanical modeling of transversely isotropic porous media in DEAL.II

In geotechnical engineering, modeling geo-structures is challenging, particularly in cases where the interaction between the structures and soil or rock is complex. Most well-known commercial modeling software is based on homogenous and isotropic materials. However, soil and rock are often modeled in heterogeneous and anisotropic media because of the inherent anisotropy of sedimentary rock masses and their stratified structure. In recent decades, coupled hydro-mechanical (HM) interactions in isotropic porous media have been studied; however, the behavior of transversely isotropic porous media is rarely considered. In addition, it is difficult for commercial software such as Plaxis and Flac3D to express complex rock formation where the anisotropy of the material and the associated cracks and fractures could be assembled into a single model. In this study, a finite element implementation using Differential Equation Analysis Library (DEAL.II), an open-source library of finite element codes, was developed to model the fully coupled HM behavior of transversely isotropic porous media. The proposed implementation can be applied to both isotropic and transversely isotropic porous media based on Biot’s theory. The developed code can be used to model poroelastic media with (1) equations of linear elasticity for the solid matrix and (2) diffusion equations for fluid flow based on mass and linear-momentum conservation laws. We verified the performance and accuracy of the code through two examples, i.e., Mandel’s problem with a compared analytical solution and a tunnel excavation process with the Flac3D software. On the basis of these numerical applications, we present the code to model the behavior of various geo-structures such as tunnels and pile–soil interactions with anisotropic materials.

Study on the Migration Law of Overlying Strata of Gob-Side Entry Retaining Formed by Roof Cutting and Pressure Releasing in the Shallow Seam

A mechanical model of a hard roof was built to analyze the pressure relief roof cutting (RCPR) process for gob-side entry retaining (GER) and identify the critical stage of roadway stability control during RCPR. Based on the mechanical analysis of key parameters of automatic roadway with RCPR, the FLAC3D software was adopted to conduct a numerical simulation to investigate the influence law of height and angle of RCPR, to analyze the trend of variations in the vertical displacement of roadway surrounding rock stress and the roof under different conditions, and to verify that the optimal roof cutting height and seam cutting angle of the 12201 working face of Halagou Coal mine are 6 m and 20°, respectively. The effect of automatic roadway with RCPR has been well implemented through conducting the bidirectional cumulative blasting test on site. To impose effective roadway surrounding rock controlling measures on Halagou Coal mine in RCPR of hard, coal-bearing roof structures at a shallow mining depth, constant resistance large deformation anchor cables, in combination with a single hydraulic prop, joist steel 11#, and steel mesh reinforcement, could provide active surrounding rock support. In addition to the active support, surrounding rock control could be strengthened using grouting bolts. Based on the result, the stress in the roadway coal side and the vertical displacement of the roof can be reduced through increasing the roof cutting height, contributing to the stability of the roadway. Increasing of the roof cutting angle will lead to the increasing of stress in the coal side of the roadway and the increasing of roof displacement with a maximum angle of 20°. Meanwhile, the peak of stress concentrating on both sides of the extreme angle is decreased. Thus, increasing the cutting roof angle at random can be unfavorable to the management of roadway roof. To develop RCPR GER, roadway surrounding rock requires greater support when the mine face passes through a cutting slot. After industrial trials, these measures are proved to be effective in controlling surrounding rock movement and developing GER.

3D Numerical Simulation-Based Targeting of Skarn Type Mineralization within the Xuancheng-Magushan Orefield, Middle-Lower Yangtze Metallogenic Belt, China

Abstract Recent exploration has identified a series of Cu-Mo skarn deposits within the Xuancheng-Magushan orefield. The orefield forms part of the Nanling-Xuancheng mining district, which is located within the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB) of central-eastern China. However, this area contains thick and widespread unprospective sedimentary cover sequences that have impeded traditional approaches to mineral exploration. This study presents the results of 3D numerical simulation modeling that identifies possible mineral exploration targets within the entire Xuancheng-Magushan orefield. This modeling enables the identification of unexplored areas with significant exploration potential that are covered by thick sedimentary sequences that cannot be easily explored using traditional exploration approaches. This study outlines the practical value of 3D numerical simulation-based targeting in areas with thick sedimentary cover sequences and uses the Flac3D software package to couple processes involved in ore formation such as stress, pressure, and heat transfer. Here, we use volumetric strain increments calculated during numerical modeling as the thermodynamic representation of the generation of space during prograde skarn formation, with this space filed by sulfides either penecontemporaneously or soon after magmatism. This process occurred during retrograde hydrothermal ore formation and the genesis of the skarn-type mineralization in this area. The results of the volumetric strain increment calculated during this numerical modeling study matches the distribution of known mineralization as well as delineating eight potential targets that have not yet been explored but represent areas of significant exploration potential within the Xuancheng-Magushan orefield, indicating these targets should be considered prospective for future mineral exploration. One of these targets was also identified during our previous Comsol-based numerical modeling of the formation of the Magushan Cu-Mo skarn deposit. The fact that this area has been identified as prospective using two different numerical modeling methods indicates that this area should be prioritized for future exploration and also validates the numerical modeling approaches used here and in our previous research that more specifically focused on the Magushan skarn deposit. Overall, our study indicates that prospectivity modeling using 3D numerical simulation-based approaches can be both effective and economical and should be considered an additional tool for future mineral exploration to reduce exploration risks when targeting mineralization in areas with thick and unprospective sedimentary cover sequences.

Optimization of staggered distance of coal pillars in multiseam mining: Theoretical analysis and numerical simulation

AbstractAimed at solving problems related to water retention and loss reduction in multiseam mining, a mechanical model of staggered distance mining was established. First, elastic and plastic slip line field theories were used to calculate the reasonable staggered distance expressions of multiseam mining. The staggered distance schemes of multiseam mining were optimized using the numerical simulation software FLAC3D. By performing an experiment comparing similar materials, the influence on water retention and loss reduction by optimal and unfavorable staggered distance schemes in multiseam mining was explored. The results showed that the σzz curve was distributed in the shape of a “peak” of the staggering distance coal pillars, the Z displacement curve was a “Л,” and the surface subsidence curve was a “W.” Each of these displayed the rule of “decrease then increase.” In staggered distance multiseam mining, the optimal staggered distance value for coal seam Nos. 2 and 3 was 40 m, while the most unfavorable staggered distance value was 0 m. The corresponding subsidence coefficients of the optimal staggered distance values were 0.29, 0.23, and 0.19, under the condition of keeping the optimal staggered distance value for coal seam Nos. 1 and 2 unchanged. These results could be beneficial in reduction of surface subsidence and may also have specific practical engineering significance.

Tunnel performance during the Puebla-Mexico 19 September 2017 earthquake

Seismic performance of tunnels during earthquakes in densely populated areas requires assessing complex interactions with existing infrastructure such as bridges, urban overpasses, and metro stations, including low- to medium-rise buildings. This article presents the numerical study of an instrumented tunnel, currently under construction on stiff soils, located in the western part of Mexico City, during the Puebla-Mexico 19 September 2017 earthquake. Three-dimensional finite difference models were developed using the software FLAC3D. Initially, the static response of the tunnel was evaluated accounting for the excavation technique. Then, the seismic performance evaluation of the tunnel was carried out, computing ground deformations and factors of safety, considering soil nonlinearities. Good agreement was observed between predicted and observed damage during post-event site observations. Once the soundness of the numerical model was established, a numerical study was undertaken to investigate the effect of frequency content in tunnel-induced ground motion incoherence for tunnels built in cemented stiff soils. A series of strong ground motions recorded during normal and subduction events were used in the simulations, considering a return period of 250 years, as recommended in the Mexico City building code. From the results, it was concluded that the tunnel presence leads to important frequency content modification in the tunnel surroundings which can affect low- to mid-rise stiff structures located nearby. This important finding must be taken into account when assessing the seismic risk in highly populated urban areas, such as Mexico City.

Numerical Simulation Study on Mining Effect of Surrounding Rock When Inclined Mining Face Passing through Empty Roadway

In the coal stopping process, it often happens that the mining face crossing empty roadway often causes increase of the advanced support pressure, and leads to problems such as roof fall and rib spalling, in response to which, taking a recovery mining face in Xipang Mine as the engineering background, and using software FLAC3D to establish the numerical analysis model of the mining face crossing empty roadway, the study on the influence of incline adjustment of the mining face crossing gob on the surrounding rock near the empty roadway. The result shows that with the decrease of the width of coal pillar between mining face and empty roadway, the vertical stress appears three shapes in turn: “saddle shape”, “platform shape” and “solitary peak shape”; stress concentration occurs at the intersection of two roadways, and the stress concentration in acute angle area is more obvious. Adjusting the inclination of the mining face and increasing the angle between the mining face and the empty roadway are beneficial to reduce the stress concentration phenomenon of the coal pillar in the triangle area, and the maximum supporting stress is reduced from 25.3 MPa to 23.5 MPa, which is more conducive to the safe passage of the mining face through the empty roadway.