FLAC3D Model Research Articles

Blasting Vibration Safety Criterion Analysis with Equivalent Elastic Boundary: Based on Accurate Loading Model

In the tunnel and underground space engineering, the blasting wave will attenuate from shock wave to stress wave to elastic seismic wave in the host rock. Also, the host rock will form crushed zone, fractured zone, and elastic seismic zone under the blasting loading and waves. In this paper, an accurate mathematical dynamic loading model was built. And the crushed zone as well as fractured zone was considered as the blasting vibration source thus deducting the partial energy for cutting host rock. So this complicated dynamic problem of segmented differential blasting was regarded as an equivalent elastic boundary problem by taking advantage of Saint-Venant’s Theorem. At last, a 3D model in finite element software FLAC3D accepted the constitutive parameters, uniformly distributed mutative loading, and the cylindrical attenuation law to predict the velocity curves and effective tensile curves for calculating safety criterion formulas of surrounding rock and tunnel liner after verifying well with the in situ monitoring data.

Safety analysis of building foundations over old goaf under additional stress from building load and seismic actions

Additional displacement of the building foundations over old goaf are prone to happen under the additional loads induced by new buildings, weakening-rock mass by mining and seismic actions, which will cause serious damage to the buildings. In order to analyze the safety of the building foundations safety over the old goaf, the structure characteristics of the strata over the old goaf was investigated and the instability conditions of overhanging rocks upon old goaf were also analyzed in this paper. The results indicate that the stability of overhanging rocks is remarkably decreased by the interactions of mining fractures, earthquake force and building load, in addition, the settlement of the foundations over old goaf is increased by the instability of overhanging rocks. According to the location of a new power plant in Yima Mine and its ambient conditions, we defined the influence scope of old goaf via resistivity tomography. Based on the seismic parameters of the construction site, a numerical FLAC3d model of the building foundation under the seismic actions and building load was developed. The numerical results are obtained as follows: the foundation of the main power house meets the requirement of 6° seismic fortification intensity; however, under 7° seismic fortification intensity, the maximum differential settlement of foundation between the neighboring pillars is close to the maximum allowable value, while the seismic fortification intensity reaches 8°, but the safety requirements will not be satisfied.

Research on Fast Conversion of Large Complex Block Model in SURPAC to Three-Dimensional Numerical Grid in FLAC3D

Existing numerical grid generation based on Surpac block model is inefficient when the grid quantity is large. This article obtains from the existing methods, summarizes the complete process, and adds the key details of it. By setting simpler nodes condensation algorithm, improving the problem of low conversion efficiency caused by the too large node number, achieving the fast effective conversion of Surpac block model to FLAC3D model by using C language programming. This new method has been used in building rock burst hazard analysis model of Ling-Long gold mine, which proves this modeling method is feasible and effective.

Study on the Conversion of GOCAD Models to FLAC3D Models

In the analysis of the GOCAD SGrid model and the FLAC3D hexahedral mesh model, a method of converting the former to the latter is proposed, and the data conversion program is prepared based on VB.NET. The purpose of building complex models in FLAC3D quickly is achieved, and the FLAC3D simplifies the pre-processing largely. Finally, the feasibility of the method is verified by a practical project.

Site Response Analysis for a Site with the Dipping Bedrock and Liquefiable Layers Using FLAC 3D

To get the precise input motion for seismic analysis of important structures located in liquefiable soil layers, this study demonstrates site response analysis using FLAC 3D [. Based on the previous earthquake diaster experiences and regulatory requirements for nuclear power plants (NPP), the seismic wave propagation in the site having dipping bedrock surface was modeled, also the excess pore water pressure during excitation process was added into the soil elements. The free-field site response model is used to generate the response spectra at different ground surface locations, and to predict the influence range of soil liquefaction. The analysis results show that soil liquefaction could reduce site amplification effect, and might have different degree of impact depending on natural frequency and soil pressure resistance of structures. The 3D model also can capture the soil unceratinties and reflect the real topographic effect in one computer run, so the current multiple one-dimensional equivalent linear analysis process could be improved. Therefore, the FLAC 3D model can fulfill nuclear regulatory requirement, and provide suitable ground-motion prediction for liquefiable soil sites and complex bedrock surface sites for the need of seismic evaluations of existing NPPs after Fukushima Dai-ichi Tragedy.

A Simple Generation Technique of Complex Geotechnical Computational Model

Given that FLAC3D (a geotechnical calculation software) is difficult to use for building large, complex, and three-dimensional mining models, the current study proposes a fast and a convenient modeling technique that combines the unique advantages of FLAC3D in numerical calculation and those of SURPAC (a mine design software) in three-dimensional modeling, and the interface program was compiled. First, the relationship between the FLAC3D and the SURPAC unit data was examined, and the transformation technique between the data was given. Then, the interface program that transforms the mine design model to calculate the model was compiled using FORTRAN, and the specific steps of the program implementation were described using a large iron and copper mine modeling example. The results show that the proposed transformation technique and its corresponding interface program transformed the SURPAC model into the FLAC3D model, which expedited FLAC3D modeling, verified the validity and feasibility of the transformation technique, and expanded the application spaces of FLAC3D and SURPAC.

Discussion on Anchor Structures’ Deterioration Analysis Parameter Caused by Reinforcement Corrosion under Erosion Environment Condition

Because of long-term chloride erosion and alternate drying-wetting effect, anchorage support structure of underground engineering is liable to reinforced corrosion and its strength is decreased. According to previous research theory and test results, reinforced corrosion to deteriorate load-bearing role of anchorage support structure system is studied by means of numerical analysis FLAC3D and idea of finite element strength reduction. The results are as follows: (1) losses in the anchor structural performance in underground engineering with corroded reinforcements are caused by three factors: losses in the effective cross-sectional area of anchoring body, losses in the mechanical performance of reinforcing bars and losses in the bond performance of anchoring body. (2) Based on reinforcement mechanical model in FLAC3D, deterioration of mechanical performance of anchor structures caused in underground engineering was analyzed due to reinforcement corrosion. And according to idea of finite element strength reduction and results of laboratory test, deterioration analysis parameter caused by corrosion can be reduced accordingly. The research results can provide the theory support to analyze corrosion deterioration of anchor structure in underground engineering using numerical simulation.

Numerical Simulation of the Deep Mining of Phosphate Ore Body Based on Digital Image Processing

Based on digital image processing, use Matlab mathematical software to write Flac3D modeling interface program, and suppress noise transported from CAD software, for establishing numerical simulation model rapidly. With the No.59 exploration line profile picture of Yunnan Phosphate Group Jinning mine as the object of study, which is transformed from the open pit to deep underground mining, to establish Flac3D model mined with the way of room and pillar method study, it shows that: (1) using the method of multi-threshold segmentation, build the appropriate mask to suppress image noise effectively; (2) with controlling the horizontal grid cell size, achieve uniform mesh of the model; mesh at the strata border with the triangular grid, for weakening the jagged edges; (3) as the stopes excavated gradually, the movement extent of roof and floor is increasing influenced by mining; the roof is relatively stable, while the stress concentration factor of room pillars is bigger, therefore some measures should be taken to prevent the mine wall caving. The numerical simulation results provide a reference for the design feasibility study of phosphate mining and have a guiding significance for parameter optimization as well.

Deformation analysis of a soft–hard rock contact zone surrounding a tunnel

The Mounigou tunnel crosses complex geological strata, mostly with surrounding rock of poor quality with an IV or V classification. Failure in the form of collapses or squeezing deformation occurred many times during the tunnel construction. Especially, in the soft and hard rock contact zone of phyllite and meta-sandstone, the deformation failure was most obvious. This paper uses the FLAC-3D modeling analytical software to establish a 3D-numerical model, on the basis of a field tracing survey and laboratory tests to analyze the stress and strain changes before and after excavation of the tunnel. After excavation there are obvious stress concentrations and differentiations near the interface of the soft-and-hard rock stratum. Stress transfers and concentrates towards the hard rock stratum while in the soft rock zone stress release could be observed to some degree. The range of plastic deformation is obviously larger in the soft rock zone than in the hard rock zone. Both differences in principal stress and principal stress ratio increase after excavation. The amplification of the difference in principal stress is larger than the augmentation of the principal stress ratio. Moreover these principal stress amplifications are smaller in the soft rock zone than in the hard rock zone. The difference in principal stress amplifications between the soft and hard rock zones, together with the fact that soft rock strength is far lower than that of hard rock, causes local “relatively high geostress” effects in the soft rock. It is the main controlling factor of the large deformation of soft rock in the tunnel. It is concluded that the large deformation in the soft and hard rock contact zone in combination with the surrounding rock deformation failure in the Mounigou tunnel and the damage of the supporting structure, belongs to the type of soft rock plastic-squeezing failure.

A New Elasto-Viscoplastic Damage Model Combined with the Generalized Hoek–Brown Failure Criterion for Bedded Rock Salt and its Application

According to the requirement of the West–East Gas Transmission Project in China, the solution-mined cavities located in the Jintan bedded salt formation of Jiangsu province will be utilized for natural gas storage. This task is more challenging than conventional salt dome cavern construction and operation due to the heterogeneous bedding layers of the bedded salt formation. A three-dimensional creep damage constitutive model combined with the generalized Hoek–Brown model is exclusively formulated and validated with a series of strength and creep tests for the bedded rock salt. The viscoplastic model, which takes the coupled creep damage and the failure behavior under various stress states into account, enables both the three creep phases and the deformation induced by vicious damage and plastic flow to be calculated. A further geomechanical analysis of the rapid gas withdrawal for the thin-bedded salt cavern was performed by implementing the proposed model in the finite difference software FLAC3D. The volume convergence, the damage and failure propagation of the cavern, as well as the strain rate of the salt around the cavern, were evaluated and discussed in detail. Finally, based on the simulation study, a 7-MPa minimum internal pressure is suggested to ensure the structural stability of the Jintan bedded salt cavern. The results obtained from these investigations provide the necessary input for the design and construction of the cavern project.

A Coupling Modeling Method with ANSYS/FLAC<sup>3D</sup> and its Application

A coupling modeling method with ANSYS/FLAC3D is put forward aiming at the technical difficulties and deficiencies in pre-processing for complex geologic body and structural engineering with FLAC3D. The coupling procedure is that, firstly, the three-dimension geometry model is built with ANSYS and the model meshes are divided. And secondly, the element and node data of the completed model built in ANSYS are exported. Based on the corresponding relationship of element and node between ANSYS and FLAC3D, the exported data above is transformed by using the interface program in FORTRAN, then the information is imported into FLAC3D. Thus the three-dimension FLAC3D model for complex engineering is generated coupling with ANSYS. With coupling method, the complex three-dimension model of arch dam-foundation system in large-scale hydroelectric project is built, and the results verify the feasibility and effectiveness of the proposed method.

Implementation of the Barcelona Basic Model into TOUGH–FLAC for simulations of the geomechanical behavior of unsaturated soils

This paper presents the implementation of the Barcelona Basic Model (BBM) into the TOUGH–FLAC simulator analyzing the geomechanical behavior of unsaturated soils. We implemented the BBM into TOUGH–FLAC by (1) extending an existing FLAC 3D module for the Modified Cam-Clay (MCC) model in FLAC 3D and (2) adding computational routines for suction-dependent strain and net stress (i.e., total stress minus gas pressure) for unsaturated soils. We implemented a thermo-elasto-plastic version of the BBM, wherein the soil strength depends on both suction and temperature. The implementation of the BBM into TOUGH–FLAC was verified and tested against several published numerical model simulations and laboratory experiments involving the coupled thermal–hydrological–mechanical (THM) behavior of unsaturated soils. The simulation tests included modeling the mechanical behavior of bentonite-sand mixtures, which are being considered as back-fill and buffer materials for geological disposal of spent nuclear fuel. We also tested and demonstrated the use of the BBM and TOUGH–FLAC for a problem involving the coupled THM processes within a bentonite-backfilled nuclear waste emplacement tunnel. The simulation results indicated complex geomechanical behavior of the bentonite backfill, including a nonuniform distribution of buffer porosity and density that could not be captured in an alternative, simplified, linear-elastic swelling model. As a result of the work presented in this paper, TOUGH–FLAC with BBM is now fully operational and ready to be applied to problems associated with nuclear waste disposal in bentonite-backfilled tunnels, as well as other scientific and engineering problems related to the mechanical behavior of unsaturated soils.

Prediction of spatial displacement development

AbstractOne of the major shortcomings of two‐dimensional approaches for underground excavation design is the (mostly) inadequate modelling of the effects of the face advance. Although they may roughly estimate the evolution of the displacements towards their final value, none of the 2D solutions available so far provide information about the extent of the pre‐relaxation the ground has undergone. On the other hand, 3D calculations pose a much greater effort in modelling and evaluation, and can be conducted only by using numerical methods.The method presented in this paper is intended to narrow this gap, representing an easy‐to‐implement tool allowing fast assessment of displacement development for a circular cavity in a linearly elastic‐ideally plastic Mohr‐Coulomb material under hydrostatic loading. A numerical parametric study has been performed on a 3D model in FLAC3D. The parameters for the numerical simulations were chosen in such a way that they form a regular grid in a co‐ordinate system spanned by the friction angle and a non‐dimensional variable defined as the ratio between the depth of failure and the tunnel radius. Based on the displacement data obtained from numerical simulations, the respective fictitious support pressures have been back‐calculated for every face position, using the closed‐form solution developed by Feder & Arwanitakis. The back‐calculated curves of the fictitious support pressure, its dimensionless form λ (equivalent support pressure coefficient), defined as the ratio between the fictitious support pressure and the primary stress respectively, have been fitted with a slightly modified version of the function proposed by Sulem et al. The fitting process yields function shape parameters, allowing the establishment of three interpolation relationships. The knowledge of the shape parameters for an arbitrary set of mechanical parameters allows the calculation of the displacement path. The results have been verified on a set of ten 3D calculations with a random set of parameters and show very good agreement in all cases. In addition, the presented method is demonstrated through case histories.