A Three-Dimensional Grouting Model Considering Hydromechanical Coupling Based on the Combined Finite-Discrete Element Method

Coupled hydro-mechanical analysis for grout penetration in fractured rocks using the finite-discrete element method

The combined finite–discrete element method (FDEM) is an advanced numerical calculation method that is highly suitable for simulating the entire rock blasting process. Considering that rock mass contains many joints, the present study introduces a rock joint constitutive model to capture the transmission and reflection phenomena of blasting stress waves when they reach the joint. At the same time, based on the original FDEM code, an optimized blasting calculation model is proposed. This model considers the effect of explosive gas and accurately describes the physical relationship between the explosive gas pressure and the change in the blasting chamber area caused by crack propagation. To overcome the limitation of previous blasting models that only apply the pressure of the explosive gas to the borehole wall, the present study optimizes the determination conditions for crack penetration and the calculation method for the blasting chamber area as well as further considered the influence of the embedding effect of explosive gas on crack propagation. Finally, through three examples, the transmission and reflection laws of stress waves at the joints and the entire process of rock mass throw blasting are simulated. The results illustrate that this model can capture the propagation of stress waves, the gas wedge effect of explosive gas, and the entire process of crack initiation, propagation, and penetration in the rock mass during the explosion, demonstrating the potential of FDEM in blasting simulation.

Purpose In order to avoid the problem of volumetric locking often encountered when using constant strain tetrahedral finite elements, the purpose of this paper is to present a new composite tetrahedron element which is especially designed for the combined finite-discrete element method (FDEM). Design/methodology/approach A ten-noded composite tetrahedral (COMPTet) finite element, composed of eight four-noded low order tetrahedrons, has been implemented based on Munjiza’s multiplicative decomposition approach. This approach naturally decomposes deformation into translation, rotation, plastic stretches, elastic stretches, volumetric stretches, shear stretches, etc. The problem of volumetric locking is avoided via a selective integration approach that allows for different constitutive components to be evaluated at different integration points. Findings A number of validation cases considering different loading and boundary conditions and different materials for the proposed element are presented. A practical application of the use of the COMPTet finite element is presented by quantitative comparison of numerical model results against simple theoretical estimates and results from acrylic fracturing experiments. All of these examples clearly show the capability of the composite element in eliminating volumetric locking. Originality/value For this tetrahedral element, the combination of “composite” and “low order sub-element” properties are good choices for FDEM dynamic fracture propagation simulations: in order to eliminate the volumetric locking, only the information from the sub-elements of the composite element are needed which is especially convenient for cases where re-meshing is necessary, and the low order sub-elements will enable robust contact interaction algorithms, which maintains both relatively high computational efficiency and accuracy.

Dynamic stability analysis of jointed rock slopes using the combined finite-discrete element method (FDEM)

As fractures in rock significantly reduce the strength as well as the stiffness of the rock mass, grouting may be required to improve the performance of the rock mass in engineering or mining projects. During grouting, mortar of cement or other materials is injected into the rock mass so that the fractures can be filled up and the rock mass can act as an integral unit. Unlike water, grouts are usually viscous and behave as non-Newtonian fluids. Therefore, the equations describing the flow of grout are more complicated and the solutions are quite difficult to obtain. The problem is further aggravated by the fact that the fractures are mostly randomly distributed, and it is rarely possible to accurately define the fractures and the distribution patterns. In this paper, a numerical model is proposed for analyzing the grouting process. The model is based on the stochastic approach, and it can provide the depth of penetration and the fluid pressure due to the flow of grout, which is modeled as a Bingham fluid, in the fractured rock mass. Parametric studies have been carried out to investigate the effects of various factors on the depth of penetration, and a regression formula is developed for calculating the penetration depth. Experiments have been carried out and their results are used to validate the present method.Key words: stochastic fractures, fractured rock mass, grout flow, grout penetration.

Masonry arches are usually composed of individual blocks or voussoirs, which are highly discontinuous and nonlinear, and it is extremely difficult or even impossible to simulate their collapse behavior using finite element methods. Therefore, a combined finite–discrete element method (FDEM) is employed to simulate the collapse behavior of dry-joint masonry arches induced by spreading supports. With finite elements incorporated into discrete elements, both the deformation of arch voussoirs and the interaction between them such as contact can be predicted accurately. Moreover, a cohesive fracture model is implemented to simulate the potential rupture of masonry voussoirs. Based on them, several examples are validated with experiments, and the results indicate that the FDEM is able to simulate the collapse of masonry arches well. Furthermore, a parametric study is conducted on selected geometric and physical parameters to investigate the collapse of masonry arches due to support movements. The influences of friction and voussoir fracture where limited attention was paid to are also examined.

Node binding scheme based realization of extrinsic cohesive zone model (ECZM) to overcome the time discontinuity problem in 2D finite-discrete element method (FDEM)

Numerical investigation of mechanical responses and failure features of coal measure strata using combined finite-discrete element method

A novel joint element parameter calibration procedure for the combined finite-discrete element method

PurposeThis paper aims to present a new numerical model for geometric nonlinear analysis of thin-shell structures based on a combined finite-discrete element method (FDEM).Design/methodology/approachThe model uses rotation-free, three-node triangular finite elements with exact formulation for large rotations, large displacements in conjunction with small strains.FindingsThe presented numerical results related to behaviour of arbitrary shaped thin shell structures under large rotations and large displacement are in a good agreement with reference solutions.Originality/valueThis paper presents new computationally efficient numerical model for geometric nonlinear analysis and prediction of the behaviour of thin-shell structures based on combined FDEM. The model is implemented into the open source FDEM package “Yfdem”, and is tested on simple benchmark problems.

A two-dimensional coupled hydro-mechanical finite-discrete model considering porous media flow for simulating hydraulic fracturing

A driving technical concern for the automobile industry is their assurance that developed windshield products meet Federal safety standards. Besides conducting innumerable glass breakage experiments, product developers also have the option of utilizing numerical approaches that can provide further insight into glass impact breakage, fracture, and fragmentation. The combined finite-discrete element method (FDEM) is one such tool and was used in this study to investigate 3D impact glass fracture processes. To enable this analysis, a generalized traction-separation model, which defines the constitutive relationship between the traction and separation in FDEM cohesive zone models, was introduced. The mechanical responses of a laminated glass and a glass plate under impact were then analyzed. For laminated glass, an impact fracture process was investigated and results were compared against corresponding experiments. Correspondingly, two glass plate impact fracture patterns, i.e., concentric fractures and radial fractures, were simulated. The results show that for both cases, FDEM simulated fracture processes and fracture patterns are in good agreement with the experimental observations. The work demonstrates that FDEM is an effective tool for modeling of fracture and fragmentation in glass.

ABSTRACT: The finely bedded structure of shale makes its mechanical behavior highly anisotropic both in terms of deformation and strength. The variations in the bedding plane thickness originates from different sedimentation processes occurred during the formation of the shale. It is well known that these features act as weakness planes in the rock matrix and thus studying the mechanical behavior of shale should incorporate the influence of bedding planes. Numerous investigations have been conducted so far to understand the influence of bedding plane orientation on the deformation and strength of shale. However, there exist only a few investigations which studied the influence that bedding plane thickness and friction might have on the mechanical response and cracking pattern of the rock. The present study discusses the results of a series of unconfined compressive test simulations conducted on shale samples with different bedding plane thickness and friction values using the combined Finite-Discrete Element Method (FDEM). The bedding planes have been discretely modeled as a distribution of preferentially oriented defects inside the rock matrix. Experimental results from the shaly facies of the Opalinus Clay at the Mont Terri Underground Research Laboratory (URL) have been used as input parameters to calibrate the numerical model. Simulation results show a difference in cracking pattern and strength of the rock owing to different bedding plane thicknesses but almost no effect due to different bedding plane frictions. 1. INTRODUCTION Shale formations play an integral role in many civil, petroleum, and environmental engineering projects. Shales not only act as an unconventional reservoir for extracting hydrocarbon resources, but also as a potential host rock for underground geological storage of nuclear wastes and as caprock for Carbon Capture and Sequestration (CCS) operations. Shale is formed through the sedimentation and subsequent hardening of fine sediments and thus it features a finely laminated and bedded structure. Platy particles tend to deposit in distinct orientations during the sedimentation of the shale causing an anisotropic texture at the macroscopic scale (Wenk et al., 2008). The layered structure of the shale makes its deformation and strength characteristics highly anisotropic at different scales, for example, at a larger scale it is attributed to the presence of bedding planes (Saroglou and Tsiambaos, 2008). The temporal variations in the sediment supply and flow velocity causes the thickness and properties of the bedding planes to differ along the deposition axis (O’Brien, 1996). These bedding planes act as weakness planes inside the rock matrix and thus understanding the shale mechanical behavior should incorporate the influence of bedding planes (Woo et al., 2021). In addition, the existence of physical discontinuities in the rock such as natural fractures or tectonic features contributes to the anisotropy at the rock mass scale.

Recent years have seen an increase in demand for the demolition of obsolete and potentially hazardous structures, including reinforced concrete (RC) structures, using blasting techniques. However, because the risk of failure is significantly higher when applying blasting to demolish RC structures than mechanical dismantling, it is critical to achieve the optimal demolition design and conditions using blasting by taking into account the major factors affecting a structure’s demolition. To this end, numerical analysis techniques have frequently been used to simulate the progressive failure resulting in the collapse of structures. In this study, the three-dimensional (3D) combined finite discrete element method (FDEM), which is accelerated by a parallel computation technique incorporating a general-purpose graphics processing unit (GPGPU), was coupled with the one-dimensional (1D) reinforcing bar (rebar) model as a numerical simulation tool for simulating the process of RC structure demolition by blasting. Three-point bending tests on the RC beams were simulated to validate the developed 3D FDEM code, including the calibration of 3D FDEM input parameters to simulate the concrete fracture in the RC beam accurately. The effect of the elements size for the concrete part on the RC beam’s fracture process was also discussed. Then, the developed 3D FDEM code was used to model the blasting demolition of a small-scale RC structure. The numerical simulation results for the progressive collapse of the RC structure were compared to the actual experimental results and found to be highly consistent.

The combined finite–discrete-element method (FDEM) is an advanced and relatively new numerical modeling technique that combines the features of the FEM with those of the discrete-element method. It simulates the transition of brittle geomaterials from continua to discontinua through fracture growth, coalescence, and propagation. With FDEM, it is possible to simulate landslides from triggering to runout and carry out landslide scenario analyses, the results of which can be successively adopted for cost-effective early warning systems. The purpose of this paper is to describe the results of the FDEM simulations of the triggering mechanism and the evolution scenarios of the Torgiovannetto di Assisi rockslide (central Italy), a depleted limestone quarry face where a rock wedge with an approximate volume of 182,000 m3 lies in limit equilibrium conditions, posing relevant issues in terms of civil protection. The results obtained demonstrate that the FDEM is able to realistically simulate the different p...