FLAC3D Software Research Articles

Experiment and Numerical Simulation of Strength and Stress Distribution Behaviors of Anchored Rock Mass in a Roadway

Due to the influence of the ground stress, mining disturbance, and other factors, the roadway surrounding rock in deep underground engineering such as mines, tunnels, and underground caverns is prone to looseness and deformation with the excavation of roadways. In such engineering, the bolt support is frequently employed to stabilize the surrounding rock. In this work, a part of the anchor and the surrounding rock were taken as a simplified model of the anchorage rock mass, and the laboratory compression test was performed on the similitude model. Then, the FLAC3D software was used to simulate varying numbers of bolts and different lateral pressure conditions, and the peak stress, the maximum principal stress field, and the anchor stress field distribution of the anchorage rock mass were obtained. The influence of bolt pretightening force and row spacing on the stability of surrounding rock was discussed using the combined arch theory. The results show that increasing the number of bolts and lateral pressure in the anchorage rock mass can significantly improve the stress value and distribution range of the maximum principal stress field and the anchorage stress field. The fluctuation of the anchorage stress field at different anchorage distances can be lessened by increasing the number of bolts (bolt density). When the lateral pressure exceeds 3 MPa, the anchorage mechanical characteristics of the anchorage rock mass tend to remain stable. The coverage of the effective anchorage stress field and the thickness of the surrounding rock anchorage composite arch can be increased by increasing the bolt pretightening force and decreasing row spacing, consequently improving the anchorage mechanical characteristics of the anchorage rock mass. The research results can be used as a theoretical reference for choosing appropriate bolt support parameters for the roadway surrounding rock.

Research on the Capacity of Underground Reservoirs in Coal Mines to Protect the Groundwater Resources: A Case of Zhangshuanglou Coal Mine in Xuzhou, China

This study analyzes the ability of coal mine underground reservoirs to protect groundwater resources. As the demand for coal mining continues to increase, the potential impact on groundwater resources around mines has become a growing problem. Underground water reservoirs, also known as coal mine underground reservoirs, have been constructed as a solution to protect water wastage in mining operations. However, there is a lack of awareness related to the ability of underground water reservoirs in mines to protect groundwater resources. In this study, we used FLAC3D software to analyze the formation process, water storage volume, and central storage location of the underground water reservoir in Zhangshuanglou Coal Mine. The results show that the damaged volume is 3.39 × 106 m3, and the groundwater resources that can be protected by coal mine underground reservoirs in the study area amount to 1.98 × 105 m3. We found that the storage capacity of underground reservoirs is more significantly affected by the extent of mining, which can be expressed as y = 49,056.44 + 255.75x + 1.46x2 (R2 = 0.995) (x ≠ 0). Additionally, the water storage location obtained through simulation can provide a reference for the construction of underground reservoir regulation and water storage projects. The results of the water quality analysis indicate that the concentrations of SO42− decreased by 42% with the closure of the mining area, and the pH also gradually converged to neutral. This highlights the significant role of underground water reservoirs in coal mines in promoting green production and protecting water resources and the environment.

Coupled rheological behavior of tunnel rock masses reinforced by rock bolts based on the non-hydrostatic stress field

The stress and deformation characteristics of the rock mass and the rock bolt reinforcement structure change over time, as a result, it is of significance to understand the coupled rheological behavior of these two systems. In this paper, we first develop viscoelastic solutions for the rock mass reinforced by rock bolts under non-hydrostatic stresses based on the distributed force model. Subsequently, the Maxwell-Maxwell (M−M) and the Maxwell-Burgers (M−B) constitutive models are applied to the rock bolts and the rock mass, respectively, and the corresponding viscoelastic analytical solutions are then obtained. Finally, the numerical software FLAC3D is used to verify the fidelity of the mechanistic model. Our results show that the lateral pressure coefficient is positively correlated with the radial stress and the radial displacement. The radial stress in the rock mass reaches a stable value with time. Furthermore, the lateral pressure coefficient has a positive correlation with the axial force in the rock bolts in elastic analysis. However, as the creep in the rock mass develops, the axial forces under different lateral pressure coefficients gradually reach a stable value. Moreover, the lateral pressure coefficient mainly affects the distribution of axial force and the slope of the axial force in the rock bolts.

Analysis of Water Supply in Hejin Sakura Valley Imitating Jiangnan-style Landscape

To ensure the domestic water and landscape water supply requirements of Hejin Sakura Valley Scenic Area, the water supply scheme of the artificial lake and scenic spot domestic water consumption assessment machine is optimized. Firstly, in view of the water resources situation in the area where the cherry blossom valley garden scenic spot is located, the necessity of pumping groundwater is pointed out; Secondly, combined with the basic information of hydrogeology and mountainous terrain, a scheme for pumping water supply from natural pipe wells is proposed; Finally, relying on FLAC3D software, three different pipe diameter pumping well models of 600mm, 700mm and 800mm are established, three-dimensional jet field analysis is carried out, and the optimal layout scheme of pipe diameter and position of pipe well is given. Studies have shown that the larger the well diameter, the greater the outlet flow rate, and the water output can be increased by 50~80m3/d for each 100mm tube well; The number of tube wells arranged is about 6, and it is recommended that a sufficient distance should be maintained between wells; The demand for pipe wells with different apertures varies between 1 and 2 mouths. The results of this paper can provide guidance for the construction of gardens in central China to solve the problem of water supply, and support and serve the construction of garden landscape.

Probe into the Influence of Water Content upon the Safety and Stability of Loess Slope Based on the Garden Project of Hejin Cherry Valley

In order to consider the influence of soil moisture content change on the slope stability of Hejin Cherry Valley Garden Project, this paper firstly selects soil samples at typical locations to obtain the shear strength test results of loess under different moisture content; Then, based on rhinoceros and FLAC3D software, the strength reduction method is used to analyze the slope stability, and the impact of water content on the slope stability is comprehensively evaluated according to the safety factor, plastic zone and shear strain. The results show that when the soil is completely dry, the cohesion and internal friction angle are both maximum; When the water content is 11%, the internal friction angle and cohesion are at a low level; Under different water content conditions, there is a watershed for slope stability. The water content is higher than 11%, and the safety factor is lower than 1.3. With the rise of water content, the maximum shear strain of the slope spreads from the toe to the slope surface. It is found in the comprehensive plastic zone the slope surface near the top of the slope is prone to landslide. The research results of this paper can provide reference and guidance for the stability and safety of loess slope after the construction of landscape architecture in Central Plains.

Numerical Analysis of the Blockage Effect of the Tunnel Drainage System on the E-Han Expressway

The discharge of groundwater and the load on the lining structure are both significantly impacted by the obstruction of the tunnel drainage system. In this study, the fluid–structure interaction model was established based on the finite difference software FLAC3D. Then, this research explored the effects of symmetric and asymmetric blockage in the circular drainpipe, the transverse drainpipe and at the pipe joint in the tunnel on the pore water pressure, displacement and stress of surrounding rock. Our research revealed the following points: (1) When a symmetrical or asymmetrical blockage occurred in a circular drainpipe, only the blocked part of the drainpipe would be affected, but the pore water pressure at the back side of the tunnel crown and side wall lining between two adjacent circular drainpipes would increase by 200%, stress increase would increase by 22% and displacement would increase by 41%. (2) When a symmetrical or asymmetrical blockage occurred in a transverse drainpipe, the pore water pressure at the back side of the tunnel crown and side wall lining between two adjacent circular drainpipes increased by a maximum of 146%, the stress on the tunnel crown lining increased by a maximum of 4% and the tunnel crown lining was displaced by 8% to a maximum extent. (3) Both symmetrical and asymmetrical blockage of the tunnel drain joint led to the failures of the circular drainpipe and the transverse drainpipe connected with the tunnel drain joint. This increased the pore water pressure on the back side of the lining between the two adjacent drain sections and had an impact on the pore water pressure, stress and displacement of the surrounding rock nearby.

Numerical Simulation of Underground Mining-Induced Fault-Influenced Rock Movement and Its Application

The F317 fault, as a major tectonic zone in the Jianshan mine area, influences the geotectonic features and geomechanical properties of the mine area. Mining operations need to be conducted within these tectonic systems, so it is important to fully study and understand the characteristics and evolution of these tectonic systems to develop reasonable mining plans and safety measures. Aiming at the problem that the existence of the F317 fault affects the stability of the west road during the mining of the security pillar at The Jianshan underground mine in Panzhihua Iron Mine, the mechanical model of the fault surface was established through the theory of material mechanics. The mechanical criterion of fault slip during the security pillar retrieval process was obtained and combined with the contact surface theory in the numerical analysis software FLAC3D. Two numerical calculation models with and without the F317 fault were established to analyze the change characteristics of the maximum tensile stress and displacement of the road protection zone under different simulation scenarios. The influence of the fault’s presence on the surface road’s stability during the security pillar retrieval process was obtained. The study results show that changes in positive and shear stresses at the fault face caused by the security pillar retrieval process are the main factors influencing the fault slip. The upper side of the fault tends to slip along the fault face during the security pillar retrieval process, which theoretically prevents the transfer of subsidence displacement caused by underground mining to the roadside (foot side of the fault). The presence of the F317 fault has less effect on the tensile stresses at the road protection zone. Still, the fault allows the tensile stresses to be concentrated at the top and bottom of the quarry and at the isolated pillar, which is more likely to cause the rock to be stretched and squeezed. Without the F317 fault, the maximum subsidence displacement at the road protection zone is 30.59 mm, the maximum X-directional displacement is 42.17 mm (both of which are greater than the safe displacement limit by 20 mm), and the maximum Y-directional displacement is 19.75 mm, which is less than the safe displacement limit by 20 mm. Compared with the case without the F317 fault, the displacement at the road protection zone with the F317 fault is smaller, with a maximum subsidence displacement of 16.92 mm, a maximum X-directional displacement of 19.63 mm, and a maximum Y-directional displacement of 3.35 mm, all of which are less than the safe displacement limits. Therefore, the presence of the F317 fault provides some protection to the west side of the road from collapse due to underground mining.

Mechanical Properties of GFRP Bolts and Its Application in Tunnel Face Reinforcement

As a new type of pre-reinforcement material for tunnel faces, glass fiber-reinforced polymer (GFRP) bolts can effectively and safely improve the stability of tunnel faces in soft surrounding rocks and speed up excavation. Therefore, in this paper, systematic research is carried out on the bond strength of GFRP bolts in tunnel faces and their relative pre-reinforcement parameters. Firstly, the effects of rebar diameter, anchorage length, and mortar strength on the bonding properties of GFRP bars were studied by indoor pull-out tests. The bond strength-slip curves under different working conditions were obtained, and the curves showed that the ultimate bond strength between GFRP bars and mortar was negatively correlated with the diameter of GFRP bars but positively correlated with the strength of the mortar. In addition, the increase in anchorage length led to a reduction in bonding strength. Secondly, inverse analysis was used to analyse the mechanical parameters of the bond performance of the anchor bars by the finite difference software FLAC3D, and the results indicated that 1/5 of the compressive strength of the GFRP bar grouting body can be taken as the ultimate bond strength to calculate the cohesive strength of the grout. Additionally, the formula of GFRP bar grouting body stiffness was revised. Finally, based on the results of laboratory tests and the inverse analysis, the numerical simulation analysis results showed that the optimal reinforcement configuration for a shallow buried tunnel face surrounded by weak rock is to use GFRP bars with a length of 17 m arranged in the center circle of the tunnel face with a reasonable reinforcement density of 1.0 bolt/m2. The calculation formula of the stiffness and cohesion strength of the GFRP bar grouting body and the reinforcement scheme proposed in this paper can provide a reference for the construction of shallowly buried rock tunnels in soft surrounding rock.

Calculation and optimization of slope reinforcement at tunnel entrances—taking manyanpo tunnel as an example

Slope reinforcement is a common method to solve the problem of slope instability, and reasonable optimization of the corresponding support parameters is crucial for practical engineering. In this paper, the slope support method of Manyanpo tunnel entrance section is taken as an example, and the theoretical calculation method is used to optimize the project cost. Combined with the orthogonal test, the sensitivity analysis of the influencing factors of the stability of the support system and the selection of the optimal parameter combination scheme are carried out. Then, based on flac3d software, the optimization scheme is compared with the original design scheme. The results show that the safety factor of the optimized scheme is increased from 1.32 to 1.43 compared with the actual project. The optimized support parameters have better control effect on the displacement of the slope, especially in the Z direction. The optimized parameters have better support effect. This study can provide reference for the optimization design of slope engineering support.

A creep-fatigue model of rock salt and its application to the deformation analysis of CAES salt caverns

The rock surrounding salt caverns used in a compressed air energy storage (CAES) system experiences the combined creep and fatigue load during an operation period, which includes the injection, idle and production stages. To ensure the safety of the CAES salt caverns over the course of the service life, investigating the mechanical response of rock salt under creep-fatigue load is critical. In this study, creep-fatigue tests of rock salt under different conditions were performed in a stress-controlled pattern. The salt axial strain under creep-fatigue load includes initial, steady and accelerated phases. The axial strain presents a continuous increment during the high stress holding time. A fatigue damage body was established to describe the effect of cyclic load on deterioration of mechanical behavior of salt rock. A novel creep-fatigue model of rock salt is proposed by connecting the elastic body, Kelvin model, fatigue damage body and nonlinear viscoplastic body in series. The test data were used to validate the established model and they correlate well with the model data. Subsequently, the proposed model was implemented in the FLAC3D software and a creep-fatigue simulation test of a cylindrical specimen wase performed. The simulation test presents a similar variation trend compared with the test data regarding the axial strain. Finally, a three-dimensional geotechnical model was proposed to analyze the deformation of CAES salt caverns during operation and the proposed law was used as the creep model of rock salt during the simulation. The simulation results between the proposed creep-fatigue model and static Norton power model are further compared.

A novel method to retain a waterproof coal pillar near water-conducting fault

AbstractReducing the width of safe coal pillar near geological structures, such as a water-conducting fault, to improve the extraction ratio of coal seam is a major concern that needs to be addressed urgently for mining shallow coal resources in China. To tackle the contradiction between improving the extraction ratio of resources and the disaster caused by reducing the width of the waterproof coal pillar, this study focuses on retaining the coal (rock) pillar near the water-conducting fault and proposes a novel method for calculating the waterproofing of the coal pillar precisely. We consider the different location relationships between the water-conducting fault, confined aquifer and coal seam, and suggest the principle of retaining the waterproofing of the coal pillar. First, we develop a mechanical model describing a waterproof coal pillar near the water-conducting fault by using elastic–plastic mechanics theory and subsequently calculate the length of plastic zone of the coal pillar under water pressure of the fault by using the limit equilibrium method. Furthermore, we use FLAC3D software to simulate the stress distribution of the coal seam roof and floor under fault water pressure. Subsequently, based on the Mohr–Coulomb strength criterion, we propose a method to calculate the width of waterproof coal pillars by combining the plastic zone with the maximum principal stress propagation line. Ultimately, we assess and discuss the accuracy and simplicity of this method by combining it with engineering methods.

Study on Paste Transformation and Parameter Optimization of Cemented Backfilling with Fine Tailings in Deep Gold Deposits

The key to cementation backfilling in underground stopes of metal mines is quality and efficiency of backfilling. Backfilling quality is inseparable from the cementitious material as well as the tailings properties. To explore the influence of different factors on the strength of the backfilling body, the ratio of backfilling cementitious materials in the preparation process of backfilling slurry was experimentally studied to determine the economical and reasonable proportion of backfilling cementitious materials. Under the multi-factor test, it is concluded that the proportion concentration of 1:6 and 66% in the cemented specimen of medium and fine tailings meets the strength requirements of the surface layer of the backfilling body. Using the numerical simulation software FLAC3D, the movement of rock mass under different backfillings is simulated, and the subsidence of overburden, the stress of the ore body, and the damage range of the plastic zone are analyzed. The results showed that, during the transition from full tailings cemented backfilling to medium-fine tailings paste backfilling, the vertical stress concentration area of the overlying strata shifts from the surrounding ore body to the backfilling body, the plastic zone decreases, and the complexity of failure forms gradually decreases. Finally, the transformation method from full tailings cementation backfilling to medium fine tailings paste backfilling is determined, and the medium fine tailings paste backfilling in a deep gold mine is realized.

Numerical Study on Deformation and Failure Characteristics of Rectangular Roadway

In the practical processes of coal mines and tunnel, rectangular roadways are widely used in the underground environment. However, the stress distribution law of the rock mass around the rectangular roadways is relatively complicated that is influenced by different parameters, such as the in situ stress, geological structure, and properties of the surrounding rock mass. It is extremely significant to conduct systematic and in-depth research regarding the stress distribution and deformation failure mechanism of the rock mass around the rectangular roadways. Based on theoretical analysis, the stress distribution law of the surrounding rock of rectangular roadway under different rock mass strength grades is studied directly through rectangular roadway in this paper. This further reveals the distribution law of secondary stress field after excavation of rectangular roadway. A coal mine intends to excavate a roadway in rock mass, and then, the rectangular roadway is simulated by FLAC3D software. Then, the strain distribution and failure types of roadway surrounding rock under different rock mass properties are obtained. The results show that the failure of rectangular roadway is mainly shear failure and tensile failure. The roof and floor of roadway are mainly tensile failure, and the side of roadway is mainly shear failure. Moreover, the stress shifting and distribution of the rock mass around rectangular roadways is a complicated dynamic variation process. The damage degree of the floor and roof of the rectangular roadway is greater than that of the two sides of the roadway. Its variation is mainly related to the strength of surrounding rock mass.

In-situ monitoring and 3D numerical analysis of reinforced face behaviour of tunnel in composite strata by considering randomly-distributed rigid cobble granules

Full-face excavation can be difficult when tunnels are constructed in composite soil containing oversized cobbles. To mitigate construction risks, a section of the mine-by experimental tunnel was excavated as part of the Kokhav Hayerden Pumping Storage Project in Israel. The response on the face was monitored by using the Modular Reverse-Head Extensometer technique and the extrusion mechanism was studied via FLAC3D software. To successfully model randomly-distributed granules mixed in the host clay matrix, a heterogeneous method was developed to nominate individual mesh zones by assigning rigid material properties through a random Numpy list. The behaviour of the response of the face was closely depicted by the proposed model, as compared to in-situ monitoring data. For stability analysis, a strength reduction method was used and demonstrated similar factors of safety to semi-analytical solutions, which suggested the anchor design at the mine-by section may be optimized for subsequent tunnel chainages. Despite the cobble granules limiting face extrusion in the mixed strata, it brought additional concern when granules constantly spall from the working face. This could be attributed to the loss of shear strength in the host material caused by a combination of excessive shear strain and stress relaxation during tunnel excavation.

Study on small coal pillar in gob-side entry driving and control technology of the surrounding rock in a high-stress roadway

The technology described as gob-side entry driving was adopted in the Zhaogu No. 1 mine to resolve the issues pertinent to mining succession tension, serious roadway deformation, and support difficulties. The key parameters of coal columns must be studied to ensure the stable support effect of along-air tunneling under high stress. A calculation for the vertical stress of a coal pillar is proposed, and the location of the breaking line in the top plate in the hollowed mining zone is determined by considering the breakage attributes of the basic uppermost large structure of the key layer, combined with the internal and external stress fields, and the limit equilibrium zone theories. FLAC3D software is employed to simulate the geological requirements of the mine, the characteristics of vertical stress of the coal pillar, and the surrounding rock of the roadway under the technical plan of leaving a 4.5-m coal pillar. The software is also used to verify and analyze the actual measurements. The outcomes suggest that the basic roof break is located at 2.65 m on the side of the coal pillar in the near mining area, and there is a trapezoidal internal stability region around the coal pillar that can provide lasting and stable support of the roadway. The displacement of the two helpers of the roadway is between 100 and 500 mm, and the displacements of the top and bottom plates are less than 300 mm, which ensures the roadway is surrounded by rock when the high-stress requirements occur. The safety of the roadway is determined under high-stress conditions.

Deformation and Failure Laws of Surrounding Rocks of Coal Roadways under High Dynamic Load and Intelligent Prediction

Under high dynamic load, roadway deformation and failure may occur, posing great challenges. As for now, few studies have been carried out on the impacts of various factors on the deformation of roadway surrounding rocks under high dynamic load, not to mention those on intelligent prediction of the deformation and failure laws. This paper fills these research gaps by studying the deformation and failure characteristics of roadway surrounding rocks and the intelligent prediction method under high dynamic load. The finite difference software Flac3D was used to analyze the influences of roadway buried depth, lithology, and side pressure coefficient on the stability of surrounding rocks and a model was constructed for deformation prediction under high dynamic load. Finally, the influence of various factors on the deformation and their weight was obtained and the deformation can be predicted in line with the BP neural network prediction theory. The results show that the prediction effect is good, with high accuracy.

Stress and Deformation Characteristics of Tunnel Surrounding Rock under Alteration

Based on a typical project in an altered rock area, this study carried out numerical simulations using the FLAC3D software to calculate the changes in the stress field, deformation field, and plastic zone of the surrounding rock during the unsupported and supported excavation of a water transfer tunnel. The degree of alteration of the surrounding rock was considered as the base point. The following results were obtained: in the unsupported state, the tunnel surrounding rock was affected by different degrees of alteration, and compressive stress concentration appeared within a certain range at the bottom of the chamber. The value of all-directional stress decreased with the deepening of the degree of alteration, while the opposite was the case for the depth of influence. The displacement changes at the bottom and side walls of the chamber were large and increased significantly with the deepening of the degree of alteration; the displacement monitoring points distributed around the tunnel exhibited the same deformation trend. The plastic zone of the surrounding rock obviously expanded as the degree of alteration deepened. The stress, deformation field, and plastic zone of the tunnel surrounding rock were effectively controlled after the adoption of support measures. The results obtained by this study can be used as a reference for similar projects in altered rock areas.

Monitoring Study of Long-Term Land Subsidence during Subway Operation in High-Density Urban Areas Based on DInSAR-GPS-GIS Technology and Numerical Simulation

During subway operation, various factors will cause long-term land subsidence, such as the vibration subsidence of foundation soil caused by train vibration load, incomplete consolidation deformation of foundation soil during tunnel construction, dense buildings and structures in the vicinity of the tunnel, and changes in water level in the stratum where the tunnel is located. The monitoring of long-term land subsidence during subway operation in high-density urban areas differs from that in low-density urban construction areas. The former is the gathering point of the entire urban population. There are many complex buildings around the project, busy road traffic, high pedestrian flow, and less vegetation cover. Several existing items require monitoring. However, monitoring distance is long, and providing early warning is difficult. This study uses the 2.8 km operation line between Wulin Square station and Ding’an Road station of Hangzhou Subway Line 1 as an example to propose the integrated method of DInSAR-GPS-GIS technology and the key algorithm for long-term land subsidence deformation. Then, it selects multiscene image data to analyze long-term land subsidence of high-density urban areas during subway operation. Results show that long-term land subsidence caused by the operation of Wulin Square station to Ding’an Road station of Hangzhou Subway Line 1 is small, with maximum subsidence of 30.64 mm, and minimum subsidence of 11.45 mm, and average subsidence ranging from 19.27 to 21.33 mm. And FLAC3D software was used to verify the monitoring situation, using the geological conditions of the soil in the study area and the tunnel profile to simulate the settlement under vehicle load, and the simulation results tended to be consistent with the monitoring situation.

Research on stress evolution law and failure characteristics of top coal in fully mechanized caving of extra-thick coal seams

In this study, based on the engineering background of the No. 8222 working face of the Tashan coal mine in Shanxi Province, China, true triaxial experiments were carried out on Geotechnical Consulting and Testing Systems rock mechanics testing machine using cubic coal samples, and the numerical simulation was conducted through the FLAC3D software. Moreover, the stress evolution law of different layers of extra-thick coal seams and the failure mechanism of top coal in the fully mechanized caving were investigated, and the failure structure model of top coal was established. The results show that there are differences in the principal stress values at different layers of the top coal.

Experimental study on uniaxial compression of sandstone-mudstone interbedded rock mass

FLAC3D software is used to simulate sand-mudstone interbedded rock mass in various conditions, and the results of its regularity are obtained. The similarity between uniaxial simulation and theoretical results is more than 99%.