scholarly journals A 3DEC Numerical Analysis of the Interaction Between an Uneven Rock Surface and Shotcrete Lining

2021 ◽  
Author(s):  
Ping Zhang ◽  
Ering Nordlund
Keyword(s):  
Numerical Study ◽  
Support Effect ◽  
Influential Factors ◽  
Numerical Analyses ◽  
Numerical Code ◽  
Rock Surface ◽  
Stress Concentrations ◽  
Circular Tunnel ◽  
Rock Tunnels ◽  
Shotcrete Lining

AbstractRock tunnels excavated using drilling and blasting technique in jointed rock masses often have a very uneven and rough excavation surface. Experience from previous studies shows that the unevenness of a rock surface has a large impact on the support effect of shotcrete lining. However, clear conclusions regarding the effect of 2D and 3D uneven surfaces were not obtained due to limited studies in the literature. The numerical analyses reported in this paper were made to investigate the influence of the surface unevenness of a circular tunnel opening on the support effect of shotcrete using a 3D numerical code (3DEC). The models were first calibrated with the help of observations and measured data obtained from physical model tests. The influential factors were investigated further in this numerical study after calibration had been achieved. The numerical analyses show that, in general, the unevenness of a tunnel surface produces negative support effects due to stress concentrations in recesses (compressive) and at apexes (tensile) after excavation. However, shotcrete sprayed on a doubly waved uneven surface has better support effect compared to shotcrete sprayed on a simply waved tunnel surface. The development of shear strength (specifically frictional strength) on the uneven interface between the shotcrete and the rock contributes to this effect, in the condition where bonding of the shotcrete does not work effectively. The interface is a crucial element when the interaction between the rock and shotcrete is to be simulated. When an entire tunnel surface is covered by shotcrete with high modulus, more failures will occur in the shotcrete especially when rock surface is uneven. Based on the numerical model cases examined, some recommendations on how to incorporate tunnel surface conditions (2D or 3D unevenness) in the design of a shotcrete lining are given.

scholarly journals Dynamic Indentation Characteristics for Various Spacings and Indentation Depths: A Study Based on Laboratory and Numerical Tests

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Jie Liu ◽  
Wen Wan ◽  
Yu Chen ◽  
Jun Wang
Keyword(s):  
Crack Propagation ◽  
Laboratory Tests ◽  
Indentation Depth ◽  
Numerical Study ◽  
Stress Concentrations ◽  
Dynamic Indentation ◽  
Indentation Force ◽  
Numerical Tests ◽  
Crack Tips ◽  
Rock Specimens

Laboratory and numerical study tests were conducted to investigate the dynamic indentation characteristics for various spacings and indentation depths. First, laboratory tests indicate that the increase in the indentation depth first resulted in enlarged groove volumes, caused by fiercer rock breakages between indentations for a fixed spacing; then, the groove volume slightly increased for further increase in indentation depth, whereas the increase in spacing restrained rock breakages and resulted in shrunken grooves. In addition, the numerical study agreed well with laboratory tests that small chips formed at the shallow part of the rock specimen at the early indentation stage, and then, larger chips formed by the crack propagation at deeper parts of the rock specimens when the indentation depth increased. With further increase in indentation depth, crushed powders instead of chips formed. Moreover, the numerical analysis indicates that crack propagation usually leads to the decrease of the indentation force and the dissipation of the stress concentrations at crack tips, whereas the cessation of crack propagation frequently resulted in the increase of the indentation force and the stress concentrations at crack tip with the increase in indentation depth.

scholarly journals Experimental and Numerical Study on Hydromechanical Coupled Deformation Behavior of Beishan Granite considering Permeability Evolution

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Z. H. Wang ◽  
W. G. Ren ◽  
Y. L. Tan ◽  
Heinz Konietzky
Keyword(s):  
Pressure Difference ◽  
Numerical Study ◽  
Volumetric Strain ◽  
Initial Pressure ◽  
Numerical Code ◽  
Permeability Evolution ◽  
Beishan Granite ◽  
Pore Pressures ◽  
Damaged Zone ◽  
Hlw Repository

Beishan granite is a potential host rock for a high-level radioactive waste (HLW) repository in China. Understanding the hydromechanical (HM) behavior and permeability evolution of Beishan granite is important for the HLW repository safety. Therefore, the granite of Beishan in Gansu province was studied. HM coupled tests are carried out on Beishan granite under different pore pressures. The results show that the initial pressure difference has little influence on permeability measurement before dilatancy starts. However, after onset of dilatancy, the permeability increases with the increasing initial pressure difference. The initial permeability of Beishan granite is about 10−18 m2 under a confining pressure of 20 MPa. In the initial loading phase, the permeability shows a relatively large reduction. Then, the permeability almost keeps constant until dilatancy starts. From dilatancy point to peak stress, permeability increases linearly with volumetric strain. The proposed permeability evolution rule is implemented into a numerical code to perform HM coupled simulations. The simulation results show that the damaged zone first appears at the model boundary and then extends to the inside, forming high volumetric strain areas. And it provides seepage channels for fluid flow. The macroscopic fracture patterns indicate that pore pressure accelerates rock degradation during HM coupling. The obtained results help to understand the damage mechanisms of granite caused by pore pressures and are of great importance for the safety of a HLW repository.

scholarly journals Micro-scale numerical study of fiber/matrix debonding in steel fiber composites

2020 ◽  
Vol 15 ◽  
pp. 155892502091072 ◽  
Author(s):  
Baris Sabuncuoglu ◽  
Stepan V Lomov
Keyword(s):  
Steel Fiber ◽  
Volume Fraction ◽  
Numerical Study ◽  
Glass Fibers ◽  
Fiber Composites ◽  
Steel Fibers ◽  
Opening Angle ◽  
Stress Concentrations ◽  
Fiber Volume ◽  
Fiber Matrix

Fiber/matrix debonding behavior of steel fiber composites is analyzed using a parametric finite element modeling procedure and compared with conventional composites with carbon and glass fibers. Cohesive surfaces are applied to fiber–matrix interface to simulate the debonding behavior, while the interface strength properties of steel fiber are obtained with and without surface treatment. The effect of various parameters on the debonding behavior is investigated, including stress concentrations, fiber diameter, fiber shape, and fiber volume fraction, using the parametric model. The influence of stress concentrations is determined to be much lower than the debonding strength. Debonding damage is more evident in larger fibers compared to smaller ones. Earlier and sudden interface separation is observed with the polygonal steel fibers compared to the circular ones. Increase in the fiber volume ratio increases the debonding opening distance but does not affect the opening angle significantly. The results can be useful for assessing possibilities to use steel fibers to increase toughness of the composites in comparison with glass and carbon reinforcement.

A 2D-PIV Study on Natural Convective Heat Transfer in a Square Enclosure With Partially Active Side Walls

2009 ◽  
Author(s):  
Massimo Paroncini ◽  
Francesco Corvaro ◽  
Alessia Montucchiari
Keyword(s):  
Holographic Interferometry ◽  
Numerical Study ◽  
Numerical Procedure ◽  
Numerical Code ◽  
Number Range ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Side Walls ◽  
Dynamic Structures ◽  
Rayleigh Numbers

The present study is an experimental and numerical analysis on the natural convection of air in square enclosures with partially active side walls. The experimental equipment is based on two different systems: an holographic interferometer and a 2D-PIV. The test cell is a square enclosure filled of air with vertical partially active side walls at different temperatures. The hot and cold regions on these sides are located in the middle of the cavity. The remaining vertical walls are made up of glass to allow an optical access to the cavity. The top and bottom surfaces of the enclosure are made up of plexiglas to reduce heat leakages. The experimental study is carried out both through the holographic interferometry, in order to obtain the average Nusselt numbers at different Rayleigh numbers, and through the 2D-PIV, in order to analyse the dynamic behaviour of the phenomenon at the same Rayleigh numbers. The average Nusselt numbers are obtained measuring the temperature distribution in the air layer trough the real-time and double-exposure holographic interferometry; the dynamic structures are the velocity vector distribution, the streamlines and the velocity maps. Finally these experimental data are compared to the results obtained through a numerical study carried out using the finite volume code, Fluent 6.2.3. The aim of this comparison is the validation of the numerical procedure. In this way it is possible to use the numerical code to enlarge the Rayleigh number range.

scholarly journals Evaluation of settlement of shallow foundations laid on unsaturated soils

2021 ◽  
Vol 337 ◽  
pp. 03005
Author(s):  
Elis Ferreira Lopes ◽  
Marcela Moreira da Rocha Moreira ◽  
Rosiel Ferreira Leme ◽  
Francisco Chagas da Silva Filho
Keyword(s):  
Unsaturated Soils ◽  
Numerical Study ◽  
Strain Curve ◽  
Shallow Foundations ◽  
Numerical Analyses ◽  
The Finite Element Method ◽  
Retention Curve ◽  
Soil Stiffness ◽  
Versus Strain

The study presents an experimental and numerical study on an unsaturated, non-plastic and poorly graded sand, originated from Fortaleza-CE, Brazil. The numerical analyses used the Finite Element Method (FEM), were performed using the UNSTRUCT software to simulate the curve stress versus strain, considering the effect of suction on soil stiffness. Characterization and determination of the retention curve were performed through filter paper tests, which were used to determine the stress versus strain curve in a double-oedometer test. Suction was considered constant along the entire test. From the numerical analyses done with UNSTRUCT software presented satisfactory results, especially in the presence of suction profiles, that show the variation of suction along of the depth. It can be concluded that higher suction values (and soil stiffness) generate lower settlements.

scholarly journals Johnson–Holmquist-II(JH-2) Constitutive Model for Rock Materials: Parameter Determination and Application in Tunnel Smooth Blasting

2018 ◽  
Vol 8 (9) ◽  
pp. 1675 ◽  
Author(s):  
Jianxiu Wang ◽  
Yao Yin ◽  
Chuanwen Luo
Keyword(s):  
Constitutive Model ◽  
High Pressures ◽  
Numerical Study ◽  
Parameter Determination ◽  
Economic Losses ◽  
Large Strains ◽  
Determination Method ◽  
Rock Materials ◽  
Rock Tunnels ◽  
Smooth Blasting

The Johnson–Holmquist-II(JH-2) model is introduced as the constitutive model for rock materials in tunnel smooth blasting. However, complicated and/or high-cost experiments need to be carried out to obtain the parameters of the JH-2 constitutive model. This study chooses Barre granite as an example to propose a quick and convenient determination method for the parameters of the JH-2 model using a series of computational and extrapolated methods. The validity of the parameters is verified via comparing the results of 3D numerical simulations with laboratory blast-loading experiments. Subsequently, the verified parameter determination method, together with the JH-2 damage constitutive model, is applied in the numerical simulation of smooth blasting in Zigaojian tunnel, Hangzhou–Huangshan high-speed railway. The overbreak/underbreak induced by rock blasting and joints/discontinuities is well estimated through comparing the damage contours resulting from the numerical study with the tunnel profiles measured from the tunnel site. The peak particle velocities (PPVs) of the near field are extracted to estimate the damage scope and damage degree for the surrounding rock mass of the tunnel on the basis of PPV damage criteria. This method can be used in the excavation of rock tunnels subjected to large strains, high strain rates, and high pressures, thereby reducing safety risk and economic losses.

Numerical Study of Transient and Steady-State Anisotropic Cylindrical Pin Fin Thermal Behavior

2019 ◽  
Vol 11 (3) ◽  
Author(s):  
Imane Aslib ◽  
Hamid Hamza ◽  
Nisrine Hanchi ◽  
Jawad Lahjomri ◽  
Abdelaziz Oubarra
Keyword(s):  
Heat Conduction ◽  
Steady State ◽  
Thermal Behavior ◽  
Temperature Profile ◽  
Numerical Study ◽  
Numerical Code ◽  
Transient Temperature ◽  
Physical Parameters ◽  
Pin Fin ◽  
Transient And Steady State

This paper deals with the transient thermal analysis of two-dimensional cylindrical anisotropic pin fin that contains tip convection and subjected to a prescribed temperature at the fin base. The heat conduction equation contains a dual second-order derivation, which precludes solving the equation by direct application of common exact methods. Therefore, an appropriate canonical mapping is selected as a solution to cancel the dual derivation of temperature in the mapped equations. The alternating-direction implicit finite difference method (ADI) performs the integration of the mapped equations in the novel space, which involve a complicate geometry. Applying the inverse spatial transformation provides transient temperature profile in the real geometry for full-field configuration. The established numerical code has been validated successfully with the analytical solutions of the usual fins (orthotropic and isotropic). The anisotropy effect is investigated by means of various contour plots of the temperature profile as well as heat transfer rate from the fin base and the effectiveness for different parameters of study (kr/kz, krz/kz , and  Bir) in transient and steady-state heat conduction. The numerical code allows the study of the thermal behavior of anisotropic, orthotropic, and isotropic cylindrical pin fin according to the geometrical and physical parameters, as well as the thermal conditions to which the pin fin is subjected. A parametric study is performed in view to compare the thermal behavior of the various pin fin kinds submitted to the same conditions.

The Possibility of Using the Ground as a Seasonal Heat Storage: The Numerical Study

2004 ◽  
Author(s):  
Pawel Olszewski
Keyword(s):  
Solar Energy ◽  
Heat Storage ◽  
Numerical Study ◽  
Storage System ◽  
Heating System ◽  
Numerical Code ◽  
Space Heating ◽  
Solar Collectors ◽  
Seasonal Heat ◽  
The One

Humankind can effectively utilize only part of the solar energy reaching a surface of the Earth. It is due to the low density of the solar radiation and its unfavorable distribution. The majority of solar energy falls to the low latitude countries, where space-heating requirements are marginal. In these countries the solar heat is used for preparing water for washing or cleaning purposes, and this process works in one, or — maximum — a few daily cycles. In countries located at higher latitudes, where space heating is necessary in cold months, the current solar energy is insufficient to meet the space heating demand. The heat storage in deep layer of the ground is the one of possible way for solution of this problem. During the heating season, energy storage is discharged supplying the heat pomp cooperating with domestic heating system and during the summer months the storage can be charged by fluid heated in solar collectors. The main aim of presented research was analysis of using the ground layer as a heat storage system in the countries located in higher latitudes. The first variable taken into consideration was the output temperature of water leaving the solar collectors. The temperature distribution in the ground depends on the inlet water temperature, primary heated in the solar collectors, and forced into vertical boreholes. The temperature field in the ground was calculated using the duFort-Frankel finite-difference numerical method. A numerical code for 3D time dependent storage simulation has been created. The next step of analysis was calculation of waters’ temperature at the borehole output during cold months when the ground storage is discharged. This water works as a low-temperature reservoir of the heat pomp supplying the dwelling heating system. The solution of the problem is focused on an optimization of all parameters for the most efficient utilization of energy stored in the ground. The numerical genetic algorithms are scheduled to use to achieve this target.

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